HomeMy WebLinkAboutCoastal Subsidence Study 2005
Coastal Subsidence in Kapoho, Puna, Island
and State of Hawaii
Prepared for:
Hawaii County Planning Department
By
Dennis J. Hwang
Reinwald O’Connor & Playdon
With Contributions from:
Dr. Benjamin Brooks
University of Hawaii
January, 2007
Coastal Subsidence in Kapoho, Puna, Island
and State of Hawaii
Prepared for:
Hawaii County Planning Department
The preparation of this report was financed in part by the Coastal Zone Management
Act of 1972, as amended, administered by the Office of Ocean and Coastal Resource
Management, National Ocean Service, National Oceanic and Atmospheric
Administration, United States Department of Commerce, through the Office of
Planning, State of Hawai`i.
A publication of the County of Hawai`i pursuant to National Oceanic and
Atmospheric Administration Award No. NA04NOS4190038 or NA03NOS4190082
and funds provided by the Office of Planning, Department of Business, Economic
Development and Tourism, State of Hawai`i.
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Table of Contents
Chapter 1 - Introduction..................................................................................................5
Chapter 2 – Subsidence and Other Coastal Hazards at Kapoho.................................9
2.1 Ongoing Subsidence at Kapoho...............................................................................9
2.2 Historical Episodic Subsidence at Kapoho............................................................10
2.3 Hurricane Risk.......................................................................................................10
2.4 Tsunami Risk.........................................................................................................13
2.5 Earthquake Risk.....................................................................................................13
2.6 Lava Risk...............................................................................................................15
Chapter 3 – Issues with the Shoreline Certification Process......................................17
3.1 Field Trip – August 17, 2005.................................................................................17
3.2 Field Trip – July 10, 2006......................................................................................23
3.3 Discussion..............................................................................................................26
3.3.1 Shoreline Certification Issues at Kapoho........................................................27
3.4 Proposed Options...................................................................................................32
3.4.1 Surface Connection.........................................................................................32
3.4.2 Using the Transition to Gravity Flow.............................................................33
3.4.3 Relying on an Increased Use of the Vegetation Line.....................................35
3.4.4 Using Arbitrary Natural or Man-made Monuments.......................................36
3.4.5 Datums, Elevation, Topography, Wave Events..............................................36
3.4.6 Waiver.............................................................................................................37
3.5 Conclusion and Recommendations........................................................................38
Chapter 4 – Coastal Hazard Mitigation and Issues with the Special Management
Area..................................................................................................................................40
4.1 Permitting New Development for Zoning Changes, General and Community Plan
Amendments and Subdivision......................................................................................40
4.2 Infrastructure Improvements..................................................................................44
4.2.1 Raising or Rebuilding Waiopae Road.............................................................44
4.2.2 Wastewater Issues...........................................................................................45
4.3 Lot Transfer...........................................................................................................45
4.3.1 Due Diligence of the Buyer............................................................................45
4.3.2 Disclosure by the Seller..................................................................................46
4.4 Home Construction................................................................................................46
4.5 Hazard Noticed – Remedial Options Evaluated....................................................49
4.5.1 Raising the Height of Existing Seawalls.........................................................49
4.5.2 Building New Seawalls...................................................................................50
4.5.3 Legal Status of Existing Seawalls...................................................................51
4.5.4 Land Exchange................................................................................................51
4.5.5 Land Acquisition.............................................................................................54
Chapter 5 – Conclusion and Summary.........................................................................55
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Appendix 1 - Summary and Analysis of Relevant Studies..........................................58
Appendix 2 - Summary and Analysis of Interviews, Meetings or Site Visits with
Affected Stakeholder and Agencies...............................................................................60
Appendix A – Measuring Ground Motion and Estimating Relative Sea Level
Change at Kapoho, Hawai’I Using Synthetic Aperture Radar Interferometry
(InSAR)............................................................................................................................64
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Chapter 1 – Introduction
This report covers the Kapoho Beach Lots and Kapoho Vacationland Hawaii
subdivisions (Figure 1-1). The Kapoho Beach Lots subdivision was approved on
July 21, 1952. The Kapoho Vacationland Hawaii subdivision was approved on May,
19, 1962. Both subdivisions are zoned RS-10, which allows for single family
residential development on lots at least 10,000 square feet. At the time that these
areas in Puna were being developed, there was little concern for the lack of
infrastructure in place, and the surrounding geological risks such as earthquakes,
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flooding, lava or subsidence.
These geological risks are directly or indirectly
related.
During the 1975 earthquake in Kalapana, the subject area is reported to have
subsided .8 ft (from USGS – Hawaii Volcano Observatory, 1995). Since then there
have been numerous reports of monthly inundation of properties, difficulty in
determining the shoreline and complications with administering the Special
Management Area because of the frequent inundation.
Figure 1-1 – Study area
includes the Kapoho
Vacationland Hawaii and
Kapoho Beach Lots
subdivisions in the Puna
District of Hawaii.
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For insight into the subdivision process for the Puna area at that time, the reader is referred to Chapter 8 of the book
Land and Power. In the book, there is history of the post World War II land development process in the Puna area. It
is reported that may units in the area were bought by out of state investors, site unseen. In particular light is shed on the
Royal Gardens Subdivision, which in 1983, lava flows entered the development and destroyed 22 homes.
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This study commenced in July of 2005 to help address the many shoreline and
hazard issues associated with the Kapoho area. This report helps to determine the
extent of inundation and provide suggested solutions, alternatives and options. This
is not an easy task, since the area is at high risk from natural hazards, which is
compounded by the issue of subsidence. In addition, many homeowners and
landowners have invested much time and money into their property. Many are
attached to the property, both financially and emotionally.
A major task of this study was to determine the magnitude of the subsidence
problem so that options and alternatives could be created that are related to the
dynamics of the area. Thus it was very important to determine if he subsidence at
Kapoho was simply episodic such as occurred during the 1975 Kalapana event, or if
there is a possibility that the subsidence is continuous and episodic. The later would
be significantly more difficult to plan for. Prior to this study, there was some
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evidence of on going subsidence in a letter from the Hawaii Volcano Observatory
and in documents from the Hawaii County Planning Department. However, the
information was not sufficiently specific in terms of the methodology and location to
determine if on going subsidence was applicable to the study area. Thus planning
decisions based on this evidence for the Kapoho Beach Lots and Vacationland area
could not be made.
During the spring of 2006, a six month extension to the study contract was
granted so that the data collection from satellite measurements to determine the
extent, level, or magnitude of subsidence could be further evaluated. This would
allow the period of study to be extended from 26 months to 37 months (satellite
measurements from February 2003 to March 2006). With the extended period of
study, a greater level of confidence in the measurements was allowed, as well as
providing insight into any subsidence trends, or temporal variability.
This report is divided into three parts to meet the three main objectives of the
study. Each of these objectives are covered in a specific chapter of this report. In
Chapter 2 and Appendix A, the subsidence was measured by satellite and analyzed to
determine if the problem is episodic only, or episodic and continuous. Specifically,
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September 17, 2001 Letter from Don Swanson of the United States Geological Observatory to Don
Swanson of the Hawaii County Planning Department. Based on leveling surveys along Highway 137 in
1976, 1986, 1987, 1989, and 1995, the Highway dropped about 0.4-0.5 inches each year relative to Hilo,
totaling 8.25 inches between 1976 and 1995. When combined with relative sea-level rise at Hilo of .16
inches per year, the relative sea-level rise for the area near the highway should be .56-.66 inches per year.
Thus total subsidence along the highway was about 13-16 inches in the 24 year period after 1976. In the
letter, there is a question if the measurements along the highway are representative of the coastline.
Although no firm answer is provided, it is stated that the measurements are probably reasonable estimates
of the shoreline as well. Since a definite answer is not provided for the shoreline area, it was a major point
of this study to determine if the coastal area is also subsiding on an ongoing basis. This was confirmed in
this report (See report and Appendix A).
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was the subsidence at Kapoho isolated to the 1975 Kalapana earthquake, or has there
been ongoing continuous subsidence after that event. A study by Dr. Benjamin
Brooks using Synthetic Aperture Radar Interferometry or (InSAR) was used to
determine if the Kapoho areas is actively subsiding. This was one of the many critical
aspects of this report and drives, to a certain extent, the recommendations in later
chapters. Chapter 2 was written to address the goal in the scope of work related to
coastal hazard mitigation:
Establish mitigative measures to address the hazards from tsunami and
storm wave action and additional catastrophic events facing the
existing and potential residential development within the study area.
In order to establish mitigative measures, it is necessary to ascertain the
relative risks of natural hazards for the area. This was a key component of this report.
The InSAR study found that the Kapoho area maybe subject to continuous subsidence
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of ~0.8 to 1.7 cm/yr +/- 0.8 cm/yr (2 standard deviations). Since subsidence can
have a significant influence on other coastal hazards, risks were discussed for
earthquakes, hurricanes, tsunamis, and other natural hazards. Hazard mitigation
measures for the Kapoho area are also discussed, but presented primarily in Chapter
4.
Chapter 3 is devoted to the shoreline certification process, and resolving the
issues currently faced by the residents and local government in obtaining a
certification when there is monthly or yearly inundation of areas. Specifically the
chapter addresses the objective in the scope of work to:
Determine the shoreline or identify a methodology to determine the
shoreline in the study area. These recommendations shall consider the
economic, environmental and legal ramifications resulting from the
existing and potential expansion of residential development and
seawall improvements within the study area.
This Chapter incorporates many of observations that were made during
numerous field trips to the site. These field trips provided insight into the difficulty
and challenges in implementing the shoreline certification process in the Kapoho area.
In addition to the field observations, numerous reports are discussed and
recommendations are provided for how the shoreline could be determined.
Several options are discussed in this Chapter. One is to use more natural and
man-made monuments that approximate the “upper reach of the wash of the waves”
and exclude gravity flow as a component of the shoreline determination. This may
result in more development pressure on the mauka side of Waiopae Road, which
3
Two standard deviations provides a 95% confidence interval that the true subsidence is within the
bracketed accuracy estimation.
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maybe a concern due to the risk of flooding and subsidence in the area. Appropriate
hazard mitigation measures are thus recommended. Another option is to use the
mauka edge of the roadway as an arbitrary cutoff for determining the shoreline
(similar to using the face or edge of a seawall or revetment). A third option is to
encourage the State to base the shoreline with increased emphasis on evidence such as
the vegetation line. For this option, the State would have the final say on its use.
Finally the option of using a shoreline certification based on tidal flooding having
connection with the open ocean is suggested as a viable alternative. While this policy
followed by the Hawaii County Planning Department has been criticized as leading to
an impasse, this option has also served to indirectly restrict development in high flood
areas. Given the nature of the subsidence found in this report, this may be the safest
and most sound option in the long-run.
In Chapter 4, the many issues dealing with the administration of the Special
Management Area are presented, including permits for new seawalls, extending the
height of existing seawalls, wastewater disposal, and permits for new structures or
existing structures. These are common issues faced by the residents and the Planning
Department for Hawaii County. The difficulty in administration is compounded by
the shoreline certification process (Chapter 3) and the risk of hazards in the area, such
as subsidence (Chapter 2). If development and construction does proceed in areas
subject to periodic inundation or subsidence, general guidelines or suggestions are
provided. Chapter 4 addresses the goal in the scope of work, which is to:
Evaluate the need to amend the special management area and
shoreline setback laws and/or rules regarding new structures and new
structures and seawalls with the study area. Recommendations shall
consider the economic, environmental and legal ramifications resulting
from the existing and potential expansion of residential development
and seawall improvements within the study area.
The recommendations and options in this report are driven by interviews with
scientists, Kapoho residents, as well as government agencies such as the Department
of Land and Natural Resources, Army Corp of Engineers, the Department of Health,
and the Hawaii County Planning Department. During the course of the study – two
formal site visits were made and two community meetings were held. At all times,
input was sought on possible solutions, concepts, strategies and options.
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Chapter 2 – Subsidence and Other Coastal Hazards at Kapoho
One of the main objectives of this report and study was to determine the nature
of subsidence in the Kapoho area and answer the key question -- is the subsidence
episodic only -- or episodic and continuous? Once the nature of subsidence was
determined, it would be possible to fit it into the overall determination of hazard risk
in the Kapoho area, and create mitigation measures that are suited to the
characteristics of this site. The development of mitigation measures for the area is
dependant on the hazard risk and is covered in Chapter 4, which deals with
administration of the Special Management Area. In this Chapter, insight into the
hazard risk is provided.
2.1 Ongoing Subsidence at Kapoho
A major portion of this project was to gather the information necessary that
would be vital for planning purposes. Most importantly, it was necessary to
determine if the subsidence at Kapoho was ongoing, and if so, what is the magnitude
of the change. Dr. Ben Brooks and his team from the Pacific GPS Facility at the
School of Ocean and Earth Science and Technology, University of Hawaii was
contacted to assist for this issue. Using Synthetic Aperture Radar Interferometry
(InSAR) techniques and radar data from the European Space Agency’s Envisat, an
estimate for subsidence at Kapoho could be determined for the period from February
12, 2003 to March 8, 2006. The full body of the report, explaining the methodology,
the results and limitations is found in Appendix A. This section contains a very brief
description of the major findings.
From the InSAR study, the immediate Kapoho region experienced average
downward vertical motions, with respect to Hilo of between ~ -0.7 and -1.6 cm/yr +/-
0.6 cm/yr. The 0.6 cm/yr. represents 2 standard deviations. Combined with the rising
sea levels measured in Hilo and believed to be representative for Kapoho, the relative
sea level rise for Kapoho has thus been estimated to be ~0.8 to 1.7 cm/yr +/- 0.8
cm/yr (2 standard deviations).
Several key points should be made from the study. First, the subsidence at
Kapoho is at least an order of magnitude greater than the sea-level change recorded at
the Hilo tide station. So local land motion dominates over relative sea-level change
for this particular area and time interval. Also the authors do not attribute the
subsidence to any particular cause as this was outside the scope of the study.
Finally the authors note, and this report concurs that the area should continue
to be monitored since so much is at stake. It is not known if there are variations in
the rate of subsidence over time and to what extent the continuous subsidence relieves
stress that over time may cause episodic larger events (see next section). In other
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words the interaction between the ongoing subsidence and historical episodic events
is not well understood.
2.2 Historical Episodic Subsidence at Kapoho
Information on historical subsidence in the area came from two sources. From
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the book “Volcanoes in the Sea – The Geology of Hawaii,” there was extensive
subsidence of the southeast coast of the island of Hawaii during both the 1975 and
1868 earthquakes. For the 1868 event, subsidence was as high as 2 meters at Apua
Point and .8 meters at Kaimu. For the 1975 event, subsidence varied from 3.5 meters
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at Keahou Landing to .24 meters at Kapoho.
Sources from both the Hawaii Volcano Observatory as well as the U.S.
Geological Survey concluded that the earthquakes of 1975, 1868 and a larger
earthquake in 1823 were not isolated random events. Instead, they appear to be
related to a long-series of similar earth movements that have created the fault systems
in the area. As gravity and magma induced stresses build up in the area, the entire
south flank tears loose along the active fault system and slides seaward, causing large
earthquakes.
From an interview with Don Swanson, Asta Mikilius, and Paul Okubo from
the Hawaii Volcano Observatory on February 28, 2006, it was found that there was
also major subsidence reported for the 1823 earthquake and minor subsidence for an
event in 1989. While it is very difficult to predict earthquake and subsidence events,
it was suggested that a magnitude 7.0 earthquake could be expected every 30 years
and something larger every 100 years.
From the history of the area, as well as applicable reports, episodic
earthquakes causing considerable ground shaking as well as significant subsidence
have occurred in the past and should be expected in the future. It is recommended in
this report that subsidence continue to be monitored. It is not known if the continuous
subsidence documented in this report since 1975 (Section 2.1) serves to relieve stress
on the fault system, and thus diminish the magnitude or frequency of future episodic
events.
2.3 Hurricane Risk
Subsidence of the coastline will serve to increase the risk from future flooding
and wave events from a hurricane or a tsunami. Each of these risks are covered with
greater detail in this Chapter. Regarding hurricane risk, all islands in Hawaii are
susceptible to this hazard. However there are two key points to be made in this
4
Macdonald, G.A., Abbott, A.T., and Peterson, F.L., 1983. Volcanoes in the Sea – The Geology
of Hawaii. University of Hawaii Press, Honolulu.
5
USGS – Hawaii Volcano Observatory, 1995.
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report. First, there is a misperception that the island of Kauai is most susceptible to
hurricanes because it has been hit directly by Hurricanes Iniki in 1992 and Iwa in
1982. Figure 2-1, from the Oahu Civil Defense Agency displays relative hurricane
risk for the Hawaiian Islands. Most of the hurricanes are formed in the east Pacific
and travel west before curving north to threaten the Hawaiian Islands. Given the
origin of these systems is in the east Pacific, the island of Hawaii, being closer to the
source is just at high a risk of being hit as Kauai, if not more.
Figure 2-1 - Relative Hurricane Risk for the Hawaiian Islands – Contours show the number of
times a hurricane passes within 75 nautical miles every ten years (Oahu Civil Defense Agency,
2003). Contours show the risk is greatest for Hawaii County, while Maui and Oahu have slightly
greater risk than Kauai.
example of the typical track for hurricanes in the
Hurricane Estelle is a good
Pacific. On July 22, 1986, the eye of Estelle passed over 100 miles south of Hawaii
County (see Figure 2-2). In addition to the high spring tide, high waves generated
from Estelle, crashed on the shores of the Big Island. There is no reason, from
Figures 2-1 and 2-2 that Kauai would be more susceptible to hurricanes than Hawaii
County.
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Figure 2-2 – Track of Hurricane Estelle from origination as a tropical storm in the east Pacific to
the formation of a hurricane and passage south of Hawaii County as a category 1 hurricane
(Graphic from Wikipedia).
The second major point in this section is that the low elevation created by
episodic or continuous subsidence makes the coastal area in Kapoho very susceptible
to flooding and wave action, from even minor systems. This was an observation
made from the two formal field trips made to the site. On August 17, 2005 and July
10, 2006, the two high tides were roughly equal (see Chapter 3). However the
increased inundation for the later date is attributed primarily to the stronger winds,
wind and wave setup, and wave action. A strong system such as a hurricane would
have an even greater impact.
Hurricane Estelle is again used to illustrate the point about the areas
susceptibility to wind and wave setup, as well as storm events. From available
reports regarding Hurricane Estelle, major damage in Hawaii occurred at the
Vacationland area. The high waves washed away 5 beachfront homes and severely
damaged dozens of others. According to records at the Hawaii County Planning
Department, 18 houses suffered minor damage that totaled $42,500. In addition, 12
houses had major damage that totaled $194,000 and 7 houses were completely
destroyed with an estimated property damage of $160,883.
Another indication of the susceptibility of this area to wave and wind events
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was indicated in an interview with local resident Eric Schott. When tropical storm
Daniel went by the Hawaiian Islands on July 28, 2006, the apparent water level at
Kapoho was much higher than the highest tides that he had seen. On the road, the
water may have been a foot higher, even though the high tide was only 2.5 feet as
indicated by the Old Farmers Almanac and the NOAA tide charts. Mr. Schott did
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Interview on August 2, 2006 with Eric Schott, homeowner at Kapoho Vacationland Subdivision.
12
accompany the survey team on August 17, 2005, when the high tide reached 3.17 feet,
but the wave and wind conditions were much less.
2.4 Tsunami Risk
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According to the Atlas of Natural Hazards in the Hawaiian Coastal Zone, the
Kapoho area has a high tsunami ranking. The Kapoho area is vulnerable to both local
and distant tsunamis.
For local tsunami activity, the history of tsunamis coincides with the history of
earthquakes in the area (See Section 2.2). According to the Atlas of Natural Hazard,
during the 1868 earthquake, a tsunami was generated that washed away 180 houses
on the Kau-Puna coast and drowned 46 people. The port town of Keauhou, near
Halape, was completely destroyed and is no longer found on maps. During the 1975
Kalapana earthquake, a tsunami was also generated along the coast and two campers
were killed by the wave at the Halape Campgrounds in Kau, boats and piers were
damaged in Hilo, houses were destroyed on the Punaluu coast, and fishing boats were
sunk in Keahou Harbor south of Kona.
For distant tsunamis, between 1812 and 1975, there have been 22 tsunamis
that have had damaging consequences to the Hawaiian shoreline. These tsunamis
came from tectonically active areas in regions of the Pacific, including Alaska, the
Aleutian Islands, Chile, Japan and Tonga. Not all have affected the southeast coast of
Hawaii county. The most notable that did include the tsunamis in 1946 (20 ft. runup),
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1952 (10 ft.), 1957 (10 ft.) and 1960 (13 ft.).
Both hurricane and tsunami risk are factors that are considered on the Flood
Insurance Rate Map (“FIRM”) under the National Flood Insurance Program. From
the FIRMs, sections of the coast are designated as flood prone (A zone) or wave
prone (V zone) and appropriate construction measures are proposed, including
elevating on piers and columns in the V zone. This elevation may protect against
tsunami waves, if the elevation is sufficiently high. However, subsidence is not
factored into the development of the applicable elevations, so over time, buildings
may be placed at higher risk as subsidence proceeds. For this reason, the concept of
free board or building extra elevation into the structure is strongly recommended (see
Chapter 4).
2.5 Earthquake Risk
The evaluation of earthquake risk in the Kapoho area is very important,
because earthquake shaking is one factor that needs to be accounted for if structures
7
Atlas of Natural Hazards in the Hawaiian Coastal Zone, Fletcher, C.H., Grossman, E.E., Richmond, B.M.,
and Gibbs, A.E., 2002, prepared for State of Hawaii Office of Planning, NOAA, USGS, and UH SOEST.
8
From Atlas of Natural Hazards in the Hawaiian Coastal Zone
13
are built for wave or flood risks by elevating on piers or columns. For example, the
higher a house is elevated on a pier or column, the more stress the pier or column will
be subject to during earthquake shaking. The building of a house on a pier or column
can create a top heavy structure and a “soft” story (the area between the ground
surface and the base of the elevated structure). The stress on the columns and piers
would be a function of many factors including the amount of elevation and the weight
on top. These are especially important factors for Kapoho because of the possibility
that any new structures may need to be elevated even higher due to subsidence (i.e.,
building in freeboard as discussed in Section 2.4).
In Figure 2-3, earthquake risk for the Hawaiian Islands is expressed as a
percentage of gravity for events that have a 10% chance of exceedance every 50
years. Earthquake risk is the greatest for the southeast portion of Hawaii County,
including the Kapoho area. This is attributed to the active volcano in the vicinity.
Because Hawaii has the greatest earthquake risk, it is in seismic zone 4 under the
Uniform Building Code. Kauai is in seismic zone 1, Oahu seismic zone 2a and Maui
zone 2b.
While it was outside the scope of this study to analyze the adequacy of the
building codes for Hawaii County, the building department should make sure that any
structures elevated on piers and columns to mitigate the damage from flooding or
wave action under the National Flood Insurance Program should also be able to
handle anticipated earthquake risk. As expressed previously, this is important
because there will be a tendency to build higher on piers and columns given the
subsidence recorded in the area. Some measures to increase column strength can be
found in the Federal Emergency Management Agency’s Coastal Construction Manual
and includes the use of cross bracing or knee bracing (see Chapter 4).
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Figure 2-3 – Earthquake Risk in Hawaii – This map from the U.S. Department of the Interior –
U.S. Geological Survey shows earthquake risk is greatest for Hawaii County, and specifically the
southeast portion of the island that includes Kapoho. The colors express the peak horizontal
acceleration as a percent of gravity for events with a 10% probability of exceedance in 50 years.
2.6 Lava Risk
That the Kapoho area is subject to lava risk is illustrated by Figure 2-4, which
shows the area of study and the boundaries of the 1960 lava flow. In the Puna
district, lava has destroyed housing in numerous areas including Kapoho, the Royal
Gardens Subdivision, Kalapana Village, Kalapana Gardens, and Kapaahu. The lava,
earthquake activity and subsidence are all related to the east rift zone of Kilauea.
Lava is a risk that should be planned for and the Hawaii Volcano Observatory is a
good source of information for this hazard.
It is instructive that after many homeowners were displaced due to the
destruction of their homes by lava, the State was involved in providing options for
relocation. A similar solution could be developed for the Kapoho area given the
proper guidelines are provided. This however, was outside the scope of this report,
but is recommended that there be follow up on this issue.
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Figure 2-4 – Map of the Kapoho Vacationland and Beach Lots subdivisions with the
boundaries of the 1960 lava flow for comparison. The Kapoho area is subject to lava risk.
Accretion by lava is the major mechanism for the coastline to build out.
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Chapter 3 – Issues with the Shoreline Certification Process
The objective for this Chapter was to: “Determine the shoreline or identify a
methodology to determine the shoreline in the study area. These recommendations
shall consider the economic, environmental and legal ramifications resulting from the
existing and potential expansion of residential development and seawall
improvements within the study area.
One important difficulty to consider in determining the shoreline for this area
is that the episodic and continuous subsidence has allowed the ocean at high water
levels to interfinger with existing development. As one moves along the coast, the
level of development changes, as well as the elevation, and thus the level of
inundation. All of this serves to complicate potential solutions. In order to gain
insight into the shoreline certification process, and other shoreline issues at Kapoho,
numerous field trips were made to the site.
3.1 Field Trip – August 17, 2005
A field trip was made on August 17, 2005, to the Kapoho Vacationland
Subdivision. Present on that day were Dennis Hwang, Dr. Ben Brooks, Dr. Chris
Foster, Larry Brown from the Hawaii County Planning Department, geology graduate
student Chris Conger, and local resident Eric Schott. The team was there to observe
the high tide predicted on the NOAA tide charts for Hilo to be at 3.1 feet above Mean
Lower Low Water (MLLW) at 2:15 pm. This was one of the highest tides of the year,
as only one day in June, three days in July and two days in August had higher
predicted tides in 2005, with the maximum in 2005 being at 3.3 feet above MLLW.
The purpose of the trip was not to identify the shoreline as defined, but to
observe one of the higher tide events for the year, which would provide insight on
methodologies to identify the shoreline in this difficult area of study.
Some observations from the field trip were:
Accretion
- There was no sign of active accretion of sand along the coastline.
The coast is made of rocky material (pahoehoe lava rock) and thus accretion,
such as occurs on some sandy beaches in the State by the buildup of loose
sediment was not present. The area to the east of the Kapoho Vacationland
and Kapoho Beach Lots subdivisions did experience lava accretion by the
1960 lava flow (Figure 2-4). The possibility of episodic accretion by lava
remains and the Hawaii Volcano Observatory should be consulted regarding
the risks for this particular area.
Subsidence Rates
- The major information on subsidence rates is derived by
previous studies, prior measurements of nearby areas, and a current study
17
using Synthetic Aperture Radar Interferometry (“InSAR”) which was
conducted by Dr. Ben Brooks and is discussed in detail in this report. This
information is found in Chapter 2 and Appendix A of this report. From field
observations alone, it is not possible to derive information on subsidence rates,
although it is possible to infer that subsidence has occurred in the past. For
instance, numerous manmade structures were flooded by the observed high
tide event.
Currents
– Associated with the incoming high tide were tidal currents. The
speed of these currents was not measured, as this was outside the scope of the
study. Generally, the currents would follow low spots and channels in the
rocky lava flows and the roadway as the tide rose. Ripples on the surface
indicted the current flow. Generally the deeper the channel, the more force
associated with the moving water.
Waves
– During the August 17, 2005 site visit, it was generally calm and the
waves broke offshore over a shallow fringing shoal. Once crossing the shoal
area, the combination of shallow water and intermittent lava barriers serve to
limit wave action. In addition, wave action is depth limited by the formula
(height of a breaking wave = .78 (depth of the water). Many of the inland
areas, including the shallow low spots on Waiopae Road that became channels
during high tide were inundated by water that was measured in inches, and
thus wave action, especially mauka of the road is expected to be negligible,
absent a larger increase in water level, perhaps associated with a storm event
or future subsidence. Since storm events are not to be included in the
shoreline certification process by definition, the high tide line at this section of
Kapoho gives a good indication of the upper reach of the wash of the waves.
However in later site visits, the important role of wind and wave action and
possible increase in water levels associated with setup from these forces was
noted as significant. So although the shoreline certification process does not
account for storm events, these events play a significant role in hazard risk for
the area. Given the low lying areas of Kapoho due to subsidence, future wave
action from large and small events would be expected to have an even greater
impact in the future.
Water Quality
- There has been some concern about the water quality of the
near shore waters, but no water quality measurements were taken as this was
beyond the scope of this report. However, the observation of the incoming
water flooding properties with visible cesspools on site indicates that if there is
any leaching of the cesspools, this could lead to a direct contribution to some
of the tide pools in the Waiopae Marine Life Conservation District. In the
Kapoho Reef watch study, leaching form cesspools was identified as the major
potential source for enterococci bacteria (Appendix 1). Any new development
18
that does not protect the wastewater from flood inundation will likely
contribute to offshore water quality degradation. Wastewater issues are the
subject of additional studies as noted in Section 4.2.2.
The main observations for the August 17, 2005 site visit had to do with the
tides. Observations were made at the site from 9:30 am – when the water was at a
low point, until well past when the high tide peaked. The extent of inundation by the
high tide for that day was mapped using two satellite GPS units provided by Dr. Ben
Brooks. These units are dual frequency receivers that operate in a kinematic mode.
The accuracy of the units are measured in centimeters, versus ten meters for the units
commonly found in commercial stores.
The team set up on site at 9:30 am and did an initial reconnaissance of the
study area. Six observation points were set up and communications to the team
members were established. The tide steadily rose, and the water crept through
channels in the fields of lava and began to breach Waiopae Road (Figure 3-1). The
progression of flooding for this high tide event is shown on Figures 3-2 to 3-4.
There are numerous low spots in the road. This may have been due to initial
construction, but appears that the tidal currents passing over the road repeatedly
served to cause erosion and make any low spots deeper than they originally may have
been. Once the water crossed the road, it spilled over to low areas on the mauka side
that are significantly below the road itself and this caused significant flooding (Figure
3-4). The flow of water to these mauka areas is more gravity flow of water than wave
action as the limited depth of water over the road limits the wave action inland of the
road.
19
Figure 3-1 - At 12:30 pm on August 17, 2005, water is beginning to cross the channels in the lava
makai of Waiopae Road. The lava topography, with numerous high and low areas, results in the
creation of tidal channels, tidal pools and tidal islets. This area would be considered the inner
pool area as designated in the Kapoho Reef watch study.
20
Figure 3-2. 12:57 PM. The incoming tide has filled the tidal channels and has crossed Waiopae
Road in four low spots.
Figure 3-3 - 1:26 PM. – The tide is continuing to rise. Once crossing the road, the water spills
over to lower areas mauka of the roadway, and floods properties mauka of the road.
21
Figure 3-4 – Water overflowing the Waiopae Road and flooding the mauka lots.
Once high tide was reached for the August 17, 2005 event, the extent of
inundation for accessible lots was marked with colored rope. The satellite GPS units
were then used to record the position of the inundation event (Figure 3-5).
Figure 3-5 – Dual frequency satellite GPS units provide high accuracy in the vertical and
horizontal dimension and were used to map the inundation levels for accessible areas.
22
From the data (Figure 3-6), there were four areas (marked by arrows) where water
breached the roadway on that date. The thickness of the arrows is a rough indication of
the magnitude of the breach. Note also that the inundation in some areas may have gone
further in than the first row of houses mauka of Waiopae Road. However the mixing of
water with tidal ponds, the limited access and thick brush prevented any significant
determination for the more inland lots.
Figure 3-6 - Inundation recorded on August 17, 2005 with the use of two satellite GPS units
(RVR1 and RVR2). High Tide was 3.17 meters from NOAA tide charts. Wind speed was 6.6
meters per second and significant wave heights were 1.97 meters as measured from the ocean
buoy southeast of Hilo. Arrows indicate where breaches in the road occurred. The width of the
arrows is a qualitative indication of the size of the channel. The close proximity of the GPS units
confirm the recorded position. For later discussion in this Chapter, only RVR2 will be utilized.
The August 17, 2005 data was then compared with another high tide event on
July 10, 2006 when the tide charts indicated a 3.13 high tide. This would be almost
the same as the predicted tide for August 17, 2005 (3.17 high tide). It would be of
interest to see how the extent of inundation changed over 11 months. Given that the
July 10, 2006 high tide event was slightly lower, all things remaining the same, the
inundation should be slightly less.
3.2 Field Trip – July 10, 2006
Although the contract for Kapoho called for only one site visit, two were made.
On July 10, 2006 another field trip to the Kapoho Vacationland subdivision was made
with Dennis Hwang, Dr. James Foster, his assistant technical helper Shanna Dacanay,
and Hawaii County Planner Larry Brown. The purpose of this site visit was to
23
observe tidal inundation again, almost one year later at a similar tidal event (3.13 vs.
3.17 predicted high tides). Any differences in tidal inundation from the previous year
could be determined. Also, the channels that breached the roadway and flooded the
lots mauka of Waiopae Rd. would be observed to determine if there was a clear
delineation where runup gave way to gravity flow, which may be important with
regard to defining the shoreline (see later sections of this report).
With regard to the channels crossing the roadway, three distinct channels were
observed, with the largest being in the middle of the study area. This is different then
on August 17, 2005, when 4 channels were observed. Apparently a greater amount of
inundation on July 10, 2006, caused two of the channels to coalesce and make one
larger one. For the middle channel, the depth of water reached 16 inches at the
highest tide. The channel to the west reached 6 inches in depth, and the one to the
east, a little under 2 inches (1 and 15/16 inch) depth. Figure 3-7 shows the level of
inundation measured for the July 10, 2006 event.
Figure 3-7 - Inundation recorded on July 10, 2006 with the use of one satellite GPS unit. High
Tide was 3.13 meters from NOAA tide charts. Wind speed was 9.4 to 11 meters per second and
significant wave heights were 2.75 to 2.69 meters as measured from the ocean buoy southeast of
Hilo.
As far as a difference in inundation, Figure 3-8 compares the inundation for
the two different time periods. On this Figure, the difference in inundation is difficult
to visualize. From the field however, the difference in inundation was more
noticeable.
24
Figure 3-8 - Comparison of the inundation events, RVR2 taken on August 17, 2005 with the
inundation recorded on July 10, 2006. From the plots, there are slight differences in inundation
that are difficult to ascertain at the map scale. Field observations and pictures show a greater
level of inundation for the July event.
From the pictures in Figures 3-9 and 3-10, the extent of inundation increased
for the July, 2006 event. At this point, it is believed that the major contributing factor
was the stronger wind and wave setup which was observed for the more recent event,
as opposed to the small amount of subsidence that may have occurred. However,
given the relatively shallow depth of the channel (less than 2 inches), this particular
area maybe especially sensitive to flooding caused by any drop that would make the
channel deeper. This would be expressed as increased inundation. Observing
inundation in this area may be an obvious indicator that subsidence may be getting
worse since the current channel is relatively shallow, so any increase of only a few
centimeters over many years may be readily apparent.
The observation of increased inundation with increased wind and wave setup
for only a minor increase in wave action indicate that given the very shallow areas
along this coast, stronger wave and storm events can have a significant impact.
25
Figure 3-9 –
Inundation near
the intersection of
Waiopae Road
and Kaheka
Street on August
17, 2005.
Maximum
inundation is
recorded by a
cord. Predicted
high tide is 3.17
feet above
MLLW.
Figure 3-10 – Maximum
inundation on July 10,
2006. Although the
predicted high tide was
less, at 3.13 above
MLLW, the inundation is
greater. This is
attributed to stronger
wind and wave setup,
but subsidence could
have also played a role.
Depth of water at the
maximum channel
depth is 1 and 15/16 of
an inch or about 5 cm.
3.3 Discussion
In this effort to map the high tide line on August 17, 2005 and July 10, 2006,
several observations and conclusions can be made. While the purpose of these field
trips were to observe the high tide event, it is conceivable that property owners and
agencies could have, or may have used these events to determine the shoreline for a
specific parcel using the traditional methods as outlined in the State’s shoreline
certification procedures. Thus the observations have several implications that relate
26
to the applicability and problems of the shoreline certification process in general and
also for this area. These issues are covered in more detail below.
3.3.1 Shoreline Certification Issues at Kapoho
There are many issues and intricacies with the shoreline certification process
in general, and in particular for the Kapoho area. Before the study for Kapoho
proceeded, there was a semi-impasse with the shoreline certification process. The
Department of Land and Natural Resources was hesitant to certify shorelines in
Kapoho area because of the implication of certifying shorelines that are mauka of
established existing lots. If the shoreline certification was an indication of a property
line, there was concern that the State may be claiming ownership of land that is
located makai of the shoreline. Because shoreline certifications were not being
performed in the Kapoho-Vacationland area, the County Planning Department was
using surface connection to the ocean as a means to process applications. For
example, when an application for a Special Management Area permit was received,
the Planning Department would ask for a determination if there was a surface
connection with the ocean. If there was, the outline of the surface connection would
be determined and a setback would be measured from that outline.
There are two key points to raise. First, a shoreline certification by itself, does
not determine ownership of land. The explanation for this was provided in a
9
consultants report reviewing the shoreline certification process.
Although the
shoreline may be indicative of where a property line is located, there is a formal
procedure to change the boundaries based on erosion of land. Until this process
occurs, there is no change in ownership of land. However, the shoreline certification
is indicative of jurisdiction. Mauka of the shoreline, jurisdiction lies with the counties
and makai, it rests with the State. So although a shoreline may shift mauka for a
particular property, the land may still be privately owned although jurisdiction may
change from the county to the State. In this scenario, the private property owner, if
building a structure on their property, may need a Conservation District Use
Application (CDUA) from the State, whereas before, a Special Management Area
permit would have been required from the county. Only if the State, or the landowner
went through formal procedures to change the boundary, would there be such a shift
in property ownership.
Related to this point, the DLNR has changed their policy in November of
2006, to accept applications for certifying the shoreline in the Kapoho-Vacationland
area. If the lot is found to be makai of the shoreline, the DLNR will not certify the
shoreline survey, but will send out a letter stating the subject property is considered
9
Fletcher, C.H., and Hwang, D.J., 1994. Shoreline Certification Review and Recommendations. Office of
State Planning – Coastal Zone Management Program, p. 76.
27
10
“submerged” lands and therefore in the Conservation District. Any activity on that
lot would require approval from the DLNR through the CDUA process. Because of
this shift in policy from the DLNR, the Hawaii County Planning Department will no
longer be involved in their past practice of making observations on surface
connection. It was also indicated that the DLNR will be using surface connection as
a means to help determine the position of the shoreline. In this regard, the minimum
tide that they will use to determine the shoreline is 2.8 feet above MLLW.
With the recent shift in DLNR policy, the emphasis of this section has changed
slightly. Previously, the Hawaii County Planning Department was active in helping
to determine which lots had surface connection and sought advice on how to
determine this within the framework of the shoreline certification process. Now, the
DLNR will take applications for shoreline certification and any advice on determining
the shoreline given in this report could affect the State process more than the county.
Nevertheless, this will still affect the county indirectly, especially if applications for
permits are taken for future development by the DLNR.
While the administrative procedural impasse dealing with the shoreline
certification process appears to have been resolved at the time of this writing, there
still remains the issue of where is the shoreline? Before continuing this discussion,
it is necessary to go into the current definitions of the shoreline. There are three
definitions that are relevant. At the State level, there is a definition in the statutes and
the one in the Department of Land and Natural Resources regulations. At the county
level, there is a definition in the Special Management Area regulations for Hawaii
County. These definitions are provided:
In the statues, the Coastal Zone Management Act has the following definition
for the shoreline (Hawaii Revised Statutes § 205A-1):
“Shoreline” means the upper reaches of the wash of the waves, other
than storm and seismic waves, at high tide during the season of the year
in which the highest wash of the waves occurs, usually evidenced by
the edge of vegetative growth, or the upper limit of debris left by the
wash of the waves.
For the former shoreline certification rules for the Department of Land and
Natural Resources § 13-222-2):
“Shoreline” means the upper reach of the wash of the waves, other than
storm or tidal waves, at high tide during the season of the year in which
the highest wash of the waves occurs, usually evidenced by the edge of
10
Part of the reason for this is the State cannot certify a shoreline unless it is located on the applicant’s
property.
28
or where there is no vegetation in the immediate
vegetative growth,
vicinity,
the upper limit of debris left by the wash of the waves.
This definition has been modified on June 3, 2006 to match that found in the
State Coastal Zone Management Act. Thus there is no longer a preference to use the
vegetation line in the State rules, and the debris line, and vegetation line are to be
given equal weight as evidence for the “upper reach of the wash of the waves.” The
definition in the Hawaii County Special Management Area Rules § 9.4 uses the same
exact definition as found in the Coastal Zone Management Act.
The concern for the former State regulatory definition had been that it placed a
preference on the vegetation line over the debris line, whereas the definition in the
Coastal Zone Management Act places equal emphasis on both. With the recent
modification of the State rules to match the statute, no preference is given to the
vegetation line or the debris line.
In recent conversations with the State DLNR, they indicate that no marker
(vegetation line or debris lines) will be used exclusively and all are potential
11
indicators for the position of the shoreline.
This is also in conformity with the
recent Supreme Court decision, Diamond and Bronstein v. State of Hawai’i, Board of
Land and Natural Resources and Carl Stephens. In this October 24, 2006 opinion, the
Court held that there is no per se rule giving primacy of the vegetation line over the
debris line in determining the “upper reach of the wash of the waves.”
From observations made during the field trips there are several issues with the
shoreline certification process, especially for the Kapoho area and in light of the
recent Supreme Court decision. These problem areas are discussed below.
The major problem with relying on the “upper reach of the wash of the
waves,” is that it can lead to highly variable, and difficult to document results within a
short distance. This can lead to determinations that do not make sense in the
administration of a coastal area. This is especially true for Kapoho. Some of these
abnormal results have been taken care of by statute or rule, but not all. Below are a
few examples of the abnormalities that can result from the current definition of the
shoreline, and the existing or proposed regulatory exclusions to address these
anomalies.
1)In recognizing that the upper reach of the wash of the waves may result in
wave inundation significantly inland from an existing house, the exclusion
was added to not consider storm or seismic waves (tsunamis). This would
prevent the result of a shoreline being placed thousands of feet inland from
existing houses.
11
Interview with OCCL – DLNR and UH Sea Grant extension agent Chris Conger on November 21, 2006.
29
2)Because high winter surf is not considered a storm or tsunami, and yet
inundation can occur hundreds of feet inland from existing houses,
exclusion has been proposed, and practiced in the field by professional
surveyors and even the State Surveyor that the high winter surf must be
annually recurring. Again, this is to avoid the result that places the
shoreline hundreds of feet inland from an existing house. Taken literally,
the shoreline could be placed along some North Shore beaches on Oahu,
inland of the coastal road and makai houses.
3)In the past, the shoreline has been placed at the toe of a revetment or base
of a seawall, even though the true upper reach of the wash of the waves
would be significantly inland of these structures. This exclusion is to
prevent the result where the seawalls or revetments, even if legally
permitted, would eventually become significantly seaward of the
12
shoreline.
4)Because there are instances where the coastal slope may dip away from the
ocean, and there is the potential for inundation to move significantly inland
not by the force of wave action and runup, but by gravity flow downhill, a
13
further exclusion has been proposed for this situation.
This is significant
in the Kapoho area and discussed briefly in a review of the shoreline
certification process for the State Legislature. This issue will be revisited
shortly.
5)In the Kapoho area, the current practice of using upper reach of the wash of
the waves or surface connection to the ocean to define the shoreline can
also lead to abnormal results. For instance in Figure 3-11, a two foot wide
channel is shown that crosses Waiopae Road. Although the boundaries of
the channel can be accurately mapped to the nearest centimeter using the
latest sophisticated instruments, the information would of little value if the
measurements have no regulatory use. If surface connection is the valid
criteria for this area, then a two foot portion of the road would be under
state jurisdiction, and the dry portion of the road under the county of
Hawaii. Although surface connection can lead to abnormal results for this
small channel, it would be more reasonable if the channel became deeper,
wider and more persistent over time. However at what point is the channel
sufficiently large to take on regulatory significance?
From the above scenarios, it is apparent that a strict literal application of
the shoreline definition, especially that which relies on wave runup or the upper
12
The current practice at the DLNR is to place the shoreline at the upper reach of the wash of the waves,
even if it is mauka of a structure.
13
State of Hawaii – Department of Land and Natural Resources, “Requesting a Review and Analysis of the
Issues Surrounding the Shoreline Certification Process for the Purpose of Establishing Shoreline
Setbacks,” Report to the Twenty-Third Legislature Regular Session of 2006. 19 pages.
30
reach of the wash of waves can lead to unusual results. For example, if the
shoreline is too far back in relation to existing structures, either exclusion has been
created, or has been proposed, or the literal interpretation has not been followed in
the field. The examples given for: (i) storm or seismic waves; (ii) large winter
waves that are not annually recurring; and (iii) water that flows inland from
gravity flow, as opposed to wave runup illustrate this point.
A sense of reasonableness to the conditions at the site is often utilized that
takes place in the interpretation of the shoreline. However, two other
complicating factors are at play. The recent Supreme Court decision indicates that
there will be less flexibility in determining the “upper reach of the wash of the
waves.” If there are any changes in the shoreline certification process, rules at the
State level would need to be changed and the State rules are already under a high
level of scrutiny. Also the indication of active subsidence in Kapoho suggests that
the State and county should not be flexible in determining the shoreline in this
area because it can lead to increased development pressure in an area that is
actively subsiding and subject to frequent flooding. So although options for
shoreline certification are given in the last part of this Chapter, it is up to the
county and/or State to determine if they will be pursued. These options are not
necessarily recommendations
since it is not the purpose of this report to set policy.
Submerged Land?
State Jurisdiction?
Shoreline?
County Jurisdiction
Figure 3-11 - During the high-tide event of August 17, 2005 – water crossed the makai ocean lots,
and then the road, causing significant flooding of the mauka lots (right) as water spilled over from
the road. Using surface connection to the ocean as a criteria to determine the shoreline can result
in portion of the road being under State jurisdiction, while the majority is under county jurisdiction.
31
3.4 Proposed Options
Four main options were identified to address the shoreline certification issues
in this area, specifically with regard to the location of the shoreline. Each of these
options has advantages and disadvantages. It should be remembered that the
difficulty in developing options is partly due to the past subsidence in the area that
allows the ocean to interfinger with current development. It should also be noted that
these options were originally developed for the County to consider, but with the
recent shift in the State policy on shoreline certifications, it is unknown the extent that
the State will follow these options. The four options presented are: (i) use of the
current county practice of surface connection; (ii) rely on an increased use of the
vegetation line; (iii) use the transition from runup or wash of the waves to gravity
flow; and (iv) set an arbitrary boundary such as the mauka edge of Waiopae road.
3.4.1 Surface Connection
One possibility for the shoreline determination is to use the current practice of
surface connection to determine the shoreline. In the past, the County of Hawaii has
used a 2.8 high tide to determine the extent of inundation and then where a setback
should be measured from. Now that the State will be actively conducting shoreline
certifications, they have indicated that the surface connection is a viable methodology
and that they will also use a 2.8 high tide as their main criteria.
The surface connection methodology is technically valid since a rising high
tide at Kapoho generally has little wave action under non-storm conditions. This is
due to shallow areas being flooded and the height of a wave is depth limited. Thus a
high tide at Kapoho will give a reasonable approximation of the maximum inundation
during a year, absent very large storm waves.
For many of the ponds found on lots mauka of Waiopae Road, and in
particular the lots that were two rows removed from the road, it is very difficult to
determine if the ponds have a surface connection to the ocean or if the water level was
raised by tidal influence by subsurface connection. This could have an impact on the
administration of the area, since submerged lands would fall under the jurisdiction of
the DLNR while those ponds or water bodies that are simply tidally influenced should
be treated as a wetland with jurisdiction under the Army Corps of Engineers.
The difficulty in determining the status of many of the ponds is due to many
factors. First, there is thick vegetative cover in many areas, which makes access and
observations to the area extremely difficult. Second, many of the ponds are very
large, and it is difficult to trace throughout the boundary of the pond, which may be
on several properties, if there is any possible surface connections. Even a small
channel can provide the necessary connection. Finally, owing to the undulating lava
topography, a circuitous route is possible for a channel to link the pond with the
32
ocean. To thus determine the status of the very inland waters would be very time
consuming and beyond the scope of this study.
There are several advantages and disadvantages of surface connection. Some
advantages are that it is technically sound and can be implemented within the current
regulatory and statutory framework with no modification to existing laws. Also it
was the practice followed by the Hawaii County Planning Department and soon to be
followed by the State. Finally, if controlling development for hazard mitigation
purposes is important, using the surface connection method will identify risky areas
that are vulnerable to future flooding, wave action and subsidence.
The disadvantage of using surface connection is that it can lead to unusual
results as seen for Figure 3-12. If surface connection is utilized, some discretion
should be provided to the implementing agency, whether it is the county or the State.
Also surface connection, while being the most conservative of the four options
discussed in this report, may still not be conservative or restrictive enough. For
example, tides higher than a 2.8 foot high tide can occur and cause greater problems
than the tides used for certification purposes. The same can be said of storm or other
very high wave events, which are excluded in the shoreline determination by
definition, but in real life can cause significant hazard risk. Also there is the
possibility of tides less than 2.8 MLLW accompanied by high non-storm waves
causing much greater inundation than a 2.8 tide by itself.
3.4.2 Using the Transition to Gravity Flow
rd
In the review of the shoreline certification process by DLNR for the 23
Legislature, a report for improved administration of the shoreline certification process
was submitted. This report was put together with the input of environmental groups
(Sierra Club), business groups (Land Use Research Foundation), administrative
organizations (DLNR, CZM – Office of Planning) and technical organizations
(University of Hawaii – Geology Department & Sea Grant). In the report, the
situation was recognized that the water position setting the shoreline should be based
14
on wave energy run-up and not gravity flow or funneling through narrow passages.
A definition for run-up was proposed that would replace the “upper reach of the wash
of the waves.” The proposed definition was:
“run-up” means that the water position setting the shoreline must be
derived exclusively by wave energy run-up and not aided by gravity or
funneling through narrow passages. Where it is unclear to what extent
the gravity flow played a part in the run-up, the transition from run-up
to gravity flow shall be interpreted as shoreline (based on evidence,
expert knowledge, and reasonable expectation).
14
DLNR report, proposed definition of runup on page 13 of the report.
33
In the DLNR report, it was proposed to specifically change the definition of
the shoreline to add the term run-up and exclude gravity flow. When a bill was
submitted to change the definition, controversy prevented its passage. However,
with the existing definition of the shoreline, the case can be made that the State and
counties can already, under their existing discretion, exclude gravity flow.
During the shoreline certification process there is much discretion, and the
State Surveyor looks at much evidence including the vegetation line and debris lines
to determine the “upper reach of the wash of the waves.” The surveyor is to
determine the upper reach of the wash of the waves, and this implies that the limit of
the force of a wave, or the limit of wave wash or runup will determine the shoreline.
Examination of Waiopae Road during maximum flooding events, such as at high tide,
will allow the surveyor to identify where water flow is by wave runup (to be
included) and not gravity flow downhill. So given reasonable discretion in the
interpretation of the existing shoreline definition, gravity flow can be excluded.
Although there may not be a need to modify the shoreline definition to exclude
gravity flow, given the recent Supreme Court decision, it may make the State
surveyor more hesitant to exclude gravity flow without changes in the definitions as
described above. Given the current sensitivity with the shoreline definition, changing
the definition in the State statutes would be hard to do. The definition could be
changed in the rules at the State level and the county level, but this would also be
difficult because of the issue, whether warranted or not, about the consistency with
the controlling State statute. Nevertheless gravity flow, could be considered in the
shoreline determination because supposedly debris lines would be caused by the
upper reach of the wash of the waves, or run-up, while gravity flow would leave
evidence looking different (e.g., no debris lines).
From comments received by the State Surveyor’s office, Department of
Accounting and General Services, gravity flow could possibly be excluded and is
characterized where water is flowing downhill at an elevation above sea-level. For
example in the case where wave washes up a beach face, overtops the dune and the
water flows downhill by gravity, the portion flowing down hill could conceivably be
excluded as evidence of the shoreline. Conversely, runup (water rushing up the slope
of a beach) or current (water moving downhill because the bathymetry is below sea
level) should be included in the location of the shoreline.
In our observations of the water flow at Kapoho, it appears that in a few places
along the mauka edge of Waiopae Road, water is flowing by gravity flow as opposed
to runup or current flow. However it is not always possible to determine along the
entire length of the road if the water is flowing mauka because of spillage and gravity
flow or run-up and currents. Generally for the larger breach and channel in Figures
3-7 to 3-9, the water is flowing by run-up or current, whereas for the smaller and
shallower channels, gravity flow may play a role in the extent of inundation. Thus,
in a few locations, such as near the intersection of Waiopae and Kaheka, where flood
34
inundation is less extensive, the shoreline could be considered seaward of the road
(e.g., where there are seawalls or natural coastal vegetation).
The advantage of excluding gravity flow as a solution is that it is technically
sound since gravity flow is not related to runup (or wave runup or the “upper reach of
the wash of the waves”). This was rightfully recognized by several technical
organizations. It is also politically acceptable solution since it utilizes a definition
proposed by various administrative, technical, environmental and business groups.
For example, the State Surveyors office was part of the review team that
recommended the exclusion for gravity flow – presumably for technical and practical
reasons. Finally it provides some discretion to the implementing agency to account
for situations as seen in Figure 3-9.
The disadvantage is that the transition is not always easy to identify. Also
excluding gravity flow will increase development pressure in areas already being
flooded and possibly getting worse. Finally, it is up to the State surveyor to make the
final decision on gravity flow issues, and given the current scrutiny of the shoreline
definition on a State wide basis, they may require a change in the State statute or
regulations or both. Under the current regulatory environment, this would be difficult
to do, although this report indicates it may be within the State’s discretion to exclude
gravity flow without a change in the rules or statutes.
3.4.3 Relying on an Increased Use of the Vegetation Line
In determining the “upper reach of the wash of the waves,” the evidence can
still be by traditional markers such as the vegetation line or debris line. Where no
debris exists, naturally occurring vegetation can be used as a marker, or evidence. At
Kapoho, it is difficult to identify debris lines and this is apparently because the major
inundation observed for shoreline determinations has been by rising tides rather than
wave action. With the paucity of information provided by debris lines, key evidence
would come from observation of inundation from high tide events, or the presence of
certain types of vegetation. However, using vegetation alone can be tricky since
certain types survive seawater inundation and thus are not good indicators of the
shoreline.
Sea grasses found along the makai side of Waiopae Road would be a poor
indicator of the shoreline because they are salt tolerant and survive monthly or even
daily inundation. Conversely, naupaka to a lesser extent, and especially milo trees are
a good indicator as their tolerance for salt water is less or non-existent. There are
some milo trees seaward of Waiopae Road at the east end near Kaheka St. These
trees are a good indication that the elevation at that location is sufficiently high so that
inundation is currently not a problem and that the shoreline should be seaward of their
presence.
35
The advantage of using vegetative evidence is that there would be no need to
change existing rules or statues. A disadvantage is that given the recent Supreme
Court decision, all evidence should be considered to determine the “upper reach of the
wash of the waves,” so there can be no per se rule, policy or determination that the
vegetation should take preference over other evidence. However, given the lack of
obvious debris line evidence in the area, vegetation does appear to be an important
indicator. Also, to what extent vegetation is used by the State to determine the
shoreline is up to the State surveyors office, but the use of trees that survive only in
fresh water appear to be valid evidence of a shoreline.
3.4.4 Using Arbitrary Natural or Man-made Monuments
Due to the anomalous results possible from the use of the shoreline definition
in general, and in particular for Kapoho, one option could be for a greater reliance on
manmade or natural features. Effort could be made to emphasize a readily
recognizable feature (natural or manmade) that approximates the “upper reach of the
wash of the waves” such as the mauka edge of Waiopae Road. An analogy to this
option would be the past practice of using the edge or base of a seawall or a revetment
as an indicator of the “upper reach of the wash of the waves, even though the real
upper reach would be much farther inland.
Using the mauka edge of Waiopae Road in certain locations as the maximum
inland extent of the shoreline may make sense for several reasons. It could be a
practical solution since all lots similarly situated from a development perspective can
be treated roughly the same. This is opposed to having one lot mauka of the road
being unaffected, while the other being unbuildable, for the simple reason that a two
foot channel of water spills over from the road. There is also precedence for such a
solution because it makes analogy to the past practice of setting the shoreline at the
edge or the base of the seawall or revetment.
A disadvantage of using the mauka edge of the road is that it would require a
change to the shoreline rules at the State level. This would be difficult to do. Also,
since the practice of using the toe of a revetment or seawall has been discontinued, the
possibility of using the edge of the road as a shoreline would be more difficult to
rationalize or justify. Finally, to treat all properties similarly situated from a
development perspective may underestimate flooding and inundation risk since it
does not account for the level of flooding on each particular property, which is
dependent on relative sea-level and the elevation of the property.
3.4.5 Datums, Elevation, Topography, Wave Events
Several possibilities were considered to address the shoreline certification
process in Kapoho, including increased use of detailed runup information, use of
water level datums and elevation. For the following reasons, these concepts were not
deemed feasible.
36
Using another method such as a set datum, elevation or topography to
determine the shoreline is ruled out in this study because it would require extensive
changes at the statutory and regulatory level. Also, on-going subsidence would make
the use of a set datum or elevation outdated after many years. Another difficulty
would be the significant topography changes within the same property.
The case can be made that the shoreline at Kapoho should not be determined
by high tide events, but high wave events. Under the current shoreline definition, this
would exclude storm and seismic (tsunami) events but not seasonal high surf from
distant swells. Actually, under the definition both high tide and wave run-up should
be considered. It was outside the scope of this study, but it is generally felt that high
tide events are most useful for Kapoho area because wave runup is limited by wave
height which is limited by the depth of water over Waiopae Road. Supposedly,
further studies could have been conducted that made a comparison of high tide events
with lesser tides coinciding with high non-storm surf. This was outside the scope of
the study. Furthermore, the need to even do this illustrates some of the problems with
the shoreline certification process. A thesis or dissertation should not be needed to
determine the shoreline, because it only determines the baseline from which other
15
regulatory or development standards apply (e.g., the setback).
3.4.6 Waiver
The Hawaii County Department of Planning could also use their power of
waiver, under their SMA rules. Under Section 9-10(B)(9) – A shoreline survey (is
required) when the parcel abuts the shoreline, except that the Director may waive the
submission of the survey when the proposed development is clearly and unmistakably
located on a shoreline parcel at a considerable distance from the shoreline. It could
be argued that the areas mauka of Waiopae Road subject to flooding by gravity flow
are a considerable distance from the shoreline. Also under the Hawaii County
shoreline setback rules, Section 11-4(c) the Planning Department may waive the
certification requirement in cases in which there may be unusual physical
circumstances or conditions of the land. The case can be made that these
circumstances apply to Kapoho given the subsidence, natural topography and existing
development.
Perhaps the waiver would be acceptable if the shoreline was occasionally
flooding but stable. However, the problem of using the waiver in the Kapoho area is
that if an area is flooding, it is likely to get worse from ongoing subsidence. It may be
possible to resolve this issue by considering the level of flooding and projecting
future flooding problems by using a rate of subsidence and the slope of the land.
15
In the 1994 report on Shoreline Certification Review and Recommendations, it was recommended that
the shoreline be interpreted in a way that is simple to identify and administrate. Thus increased emphasis
on the vegetation line was proposed. Fletcher and Hwang – 1994.
37
However, this can be difficult to do since the rate of subsidence in this report is based
on three years of data and ideally the area should continue to be monitored. Also,
-4
while there is a general regional slope of 3.5 X 10 degrees, there is much variation
from lot to lot. So while attempting to plan for ongoing subsidence events is
theoretically possible to do, it is difficult to do in practice and episodic events such as
a large earthquake, hurricane, tsunami or subsidence event further complicate this
option.
When the Hawaii County Planning Department was conducting observations
for certain applications to determine surface connection, the State Surveyor, Reid
Siarot, indicated that their Department may be open to a waiver of the shoreline
certification process for those lands mauka of Waiopae Road. Now that ongoing
subsidence has been indicated, and the DLNR is taking the lead again in shoreline
16
determinations, it remains to be seen if this is an option they would entertain.
3.5 Conclusion and Recommendations
The shoreline recommendations and options discussed in this section may be
viable, but it is the final say of the State Surveyor to determine the manner by which
shorelines will be certified. The State Surveyor’s office will examine each certification
on a case by case basis. So, although the proposals in this report appear sound, a check
should be made at the applicable agencies (DLNR, County of Hawaii Planning
Department and Army Corps of Engineers).
The option to exclude gravity flow in determination of the shoreline would affect
primarily a few houses immediately mauka of Waiopae Road. If gravity flow were
excluded, development pressure will likely increase for a few areas. This has pluses and
minuses. On one hand, the investment that landowners have placed in the property can
be partly recovered. Interviews with some landowners have indicated that their main
concern is whether they can build on some of the vacant lots in this area. On the other
hand, the area is subject to flooding, tsunamis and hurricanes and therefore, some of the
areas are at high risk from natural disasters. Ongoing subsidence will increase this risk.
Thus hazard mitigation and disaster risk reduction will need to be addressed in a more
robust manner. This is covered in subsequent sections of this report.
Of course each lot will have to be examined on a case by case basis, and rough
generalizations are applied. For many of the lots makai of Waiopae Road, the
clarification of the shoreline to exclude gravity flow should not affect these lots greatly.
There will still be an issue of flooding of these lots, and whether they can be built on.
However, it should be noted that the lots makai of Waiopae Road, but towards Kaheka
16
Also by interview with the Army Corps of Engineers, the Corps is unlikely to claim an open water
connection for the channels crossing Waiopae Road (Figure 2-7), although they will treat tidal ponds makai
of the road as wetlands.
38
Street are sufficiently high so that the shoreline can be interpreted, using natural coastal
vegetation, as seaward of those houses.
Many of the options presented are not mutually exclusive. For example, the
recent Supreme Court decision indicates that during a shoreline certification, all relevant
evidence for the “upper reach of the wash of the waves should be included.” This would
include inundation as indicated by determining surface connection and flooding during a
high tide event, as well as vegetation that is not salt tolerant. Whether inundation by
gravity flow is relevant evidence could be a factor for the State surveyor to determine.
39
Chapter 4 – Coastal Hazard Mitigation and Issues with the
Special Management Area
This Chapter covers specific issues that the Planning Department for the
County of Hawaii asked to be addressed related to administration of the Special
Management Area, the shoreline setback and coastal hazard mitigation. The major
issues that the Planning Department asked to be addressed fit into one or more of the
various stages of development as shown in Figures 4-1 and 4-2. These issues
include:
(i)Permitting new development for zoning changes, general and community
plan amendments and subdivision. What does the county do for new
permits for development? (Stages 1-4)
(ii)Infrastructure Improvements – such as building, maintaining or raising
Waiopae Road to reduce inland flooding. Another key infrastructure issue
is wastewater disposal at Kapoho. (Stage 5)
(iii)Lot Transfer – the process of buying or selling existing lots and houses.
This is a major issue at Kapoho, especially with regard to disclosure.
(Stage 6)
(iv)Building new homes with appropriate hazard mitigation measures to
reduce the risk of flooding, wave action and earthquake motion. (Stage 7)
(v)Addressing hazard mitigation issues after the fact, or after the area has
been developed without the use of the preferred mitigation measures –
(e.g., new seawalls, raising the height of existing seawalls, legal status of
existing sea walls, land swaps). (Stage 8)
Since the Kapoho area is highly susceptible to natural hazards, and the area is
already developed, the later part of this Chapter discusses additional solutions and
options that can be pursued by the affected parties.
4.1 Permitting New Development for Zoning Changes, General
and Community Plan Amendments and Subdivision
Given the history of natural hazards in the area, the potential for future
hazards, as well as the geological setting, (Chapter 2), it is very important to plan for
future events at Kapoho. Because of the issue of episodic and ongoing subsidence,
the proper siting of coastal structures is especially important.
The best time to address hazard mitigation measures and the use of siting to
reduce risk from future flooding and wave risks is during the early stages of
40
development (i.e., zone changes, general and community plan amendments and the
subdivision process). This report recommends that the issue of natural hazards be
planned for at all stages of development as explained in the “Hawaii Coastal Hazard
17
Mitigation Guidebook.” This is especially important if hazard mitigation measures
for both siting and construction are to be implemented (Figure 4-1).
Figure 4-1 – From the
Hawaii Coastal Hazard
Mitigation Guidebook.
Given the number of natural
hazards in the Kapoho area,
both siting and construction
measures for hazard
mitigation are
recommended. Siting
measures are best
addressed at the early
stages of development, e.g.,
during zoning, general and
community plan changes
and the process of
subdivision
.
The earlier in the development process hazard mitigation issues are addressed,
the easier it will be to implement the measures for several reasons such as property
rights, and market value of the property (Figure 4-2). Thus this report recommends
planning for natural hazards at Kapoho and adjacent areas very early in the
development process.
Figure 4-2 – From the
Hawaii Coastal Hazard
Mitigation Guidebook. As
each stage in development
proceeds, the landowner
invests more time and
money into the project. This
serves to increase the
market value of the property
(column 1) and the
investment backed
expectations of the
landowner (column 2), which
is related to property rights.
This will result in the
community having less input
into the project and the
number of options the
government has to reduce
hazard risks will diminish
(e.g., buying the property).
17
Report prepared for the Office of Conservation and Coastal Lands, DLNR, Coastal Zone Management
Program, Office of Planning, State of Hawaii; University of Hawaii Sea Grant College Program; and the
Pacific Services Center and Coastal Services Center of NOAA.
41
For this reason, it is also suggested that the issue of hazards be addressed
through an assessment of hazard risk for Kapoho and adjacent areas. The hazard
assessment can address issues specific to a particular area on a case by case basis. A
guideline for a hazard assessment is found in Figure 4-5 of the Hawaii Coastal Hazard
Mitigation Guidebook.
The question may arise under what authority an assessment of hazards can be
requested to the potential applicant of a project. The county should have sufficient
authority under their SMA rules, the EIS process or their subdivision regulations.
Under both the SMA and EIS process, the objectives and policies in HRS-205A are
applicable and include the policy to “Reduce hazard to life and property from
18
tsunami,storm waves, stream flooding, erosion, subsidence, and pollution.” Under
the Hawaii County Subdivision regulations, “A lot shall be suitable for the purposes
for which it is intended to be sold. No area subject to periodic inundation which
endangers the health or safety of its occupants may be subdivided for residential
19
purposes.” From the same code is found, “The lot size, width, shape and
orientation, and the minimum building setback lines shall be appropriate for the
20
location of the subdivision, the type of development and the uses contemplated.”
So initially, there may be little need to amend the Special Management Area or
shoreline setback laws for siting changes in the early stages of development.
Although the need may not be critical, it may be a good practice to amend the rules to
provide additional notice to landowners on restrictions that may be in place due to the
problems with subsidence.
Once hazards are assessed, there will be many remaining issues and questions.
At least two options are presented in this report. First, the county could try and
restrict development in flood inundation areas through the zoning process or before
subdivision. Some parameters that can be used include an estimated local rate of
subsidence, a time period related to the life expectancy of the structure or useful life
of a project or subdivision, and a local or regional slope. With this information, a
potential inundation zone, or setback in the future could be roughly estimated and the
area protected from future development. Information in this report is provided on
one way to implement a setback since a regional slope is provided as well as a local
rate of subsidence based on three years of data. The setback option would be
protective, but also restrictive.
One disadvantage of the setback option is that it can lead to a very large area
that cannot be developed. One advantage is that the large area may be needed
because while it may be possible to account for steady ongoing subsidence, it will be
difficult to account for catastrophic events like episodic subsidence, hurricanes and
18
Hawaii CZM Act – HRS Section 205A – 2(b)(6)(A). Applicable portions are emphasized in italics.
19
Hawaii County Code Section 23-37
20
Hawaii County Code Section 23-32
42
earthquakes. Unfortunately the Kapoho area appears to be subject to the steady
predictable changes as well as the episodic, unpredictable ones.
Another option is to utilize a concept initially proposed by the County of
Hawaii Planning Director Chris Yuen, that is of a rolling easement. The rolling
easement concept was initially developed in Texas and is described in a Maryland
21
Law Review article by James Titus. Under the rolling easement concept, the
landward migration of the coastline cannot be stopped by hardening such as with
seawalls or revetments (Figure 4-3). Before development proceeds the expectation is
built into the project that the landowner cannot stop the sea if there is a landward
migration that threatens structures. Once the shoreline moves sufficiently inland, so
that the property line is landward of the structure, the landowner is required to remove
the structure. Thus the land areas near the shoreline can be developed, but any
migration sufficiently inland will result in the structures removal.
Figure 4-3 – The rolling
easement concept allows
construction near the shore,
but requires the landowner to
recognize prior to
development the unstable
nature of the shoreline. As
the shoreline migrates inland
in this example, the
landowner is prevented from
stabilizing the shoreline
artificially. Eventually when
the footprint of the property is
on public land, it is required
that the house be removed.
From Titus, J.G., 1998.
The advantages of the rolling easement are the disadvantages of the setback
and vice versa. The rolling easement allows the shore to be developed, so that there
is economic utility. Conversely, it can allow development very close to the ocean in
places that are vulnerable to future hurricanes, tsunamis, episodic subsidence and
even minor storms. Another disadvantage of the rolling easement is that it may be
21
Titus, J.G., Rising Seas, Coastal Erosion, and the Takings Clause: How to Save Wetlands and Beaches
without Hurting Property Owners, Maryland Law Review, 1998, vol. 57, pg. 1279.
43
difficult for homeowners to abandon their property after a certain triggering event as
they may become emotionally and financially attached to the property. This maybe
overcome by creating a very strong investment backed expectation into the property
before building that the useful life of the property will end when the shoreline
migrates sufficiently inland. This expectation would have to survive different
ownership, so that disclosure during the sale of property is vital (see Section 4.3).
It is also possible that a hybrid of a setback and rolling easement could be
employed in different percentages. In choosing between the options, or a mix of the
options, at least two factors to consider are:
1)What stage of development the project is in. If the project has already
been zoned, subdivided and infrastructure is in, it may be more
difficult legally to employ the setback.
2)What is the threat to life, as opposed to property? If developing closer
to shore will place inhabitants at risk, a more conservative approach
would be appropriate, versus if only property was at risk. Things to
consider would be the ability to evacuate and the frequency of
occurrence of natural disaster events.
There are many examples of subdivisions in the Puna District that were
developed with little consideration for the hazards in the area (Kapoho, Royal
Gardens, Kalapana, and Kapaahu). The problems in these areas provide a reminder of
the importance for planning for hazards during the zoning, general and community
planning and subdivision stages of development, when land-use tools such as a
setback or rolling easement are most effective.
4.2 Infrastructure Improvements
There are two infrastructure improvement issues that the Hawaii County
Planning Department and the residents of Kapoho specifically asked to be addressed.
These relate to the raising of Waiopae Road to prevent flooding mauka of the road
and also wastewater disposal issues.
4.2.1 Raising or Rebuilding Waiopae Road
During the October 19, 2006 community meeting for the Kapoho community,
numerous residents brought up the possibility of raising or repairing Waiopae Road to
serve as a barrier to prevent flooding of inland properties. While raising or repairing
the road can provide some protection to properties mauka of the roadway, a concern
was raised by other residents in attendance about the impact to properties makai of the
roadway and the possibility of increased flooding. This was expressed by
homeowners in the audience that were situated makai of Waiopae Road.
44
If the roadway is raised or repaired to act as a barrier, which on its face seems
as a viable solution, it is recommended that either the properties makai of the roadway
provide consent or they be encouraged to move off the property by the mechanism of
a land swap or buyout (see later sections of this Chapter). Alternatively, it maybe
possible that a study examining flooding can determine and certify that there would
be no adverse impact on lots makai of the improvement. Without an official study on
this specific issue, it should be assumed that the improvements that build up Waiopae
road will increase flooding on the makai lots.
4.2.2 Wastewater Issues
At the beginning of the Kapoho study, wastewater issues were of concern to
the residents and were one of the outstanding issues to be addressed. Since the start
of this study, Senate Bill 2480 was approved by the State legislature and appropriated
$150,000 specifically to study wastewater options for both the Kapoho Vacationland
and Beach Lots area. Since this major funding was approved and released by the
Governor’s office specifically for wastewater issues, the importance of addressing
wastewater, which is a very small component of this report is minimized. It is
suggested however that the factor of subsidence be considered in the future study
commissioned by Senate Bill 2480. This Bill was introduced by Senator Russell
Kokubun.
4.3 Lot Transfer
In the interview with numerous residents and other government organizations,
it became apparent that many landowners and homeowners in Kapoho bought their
properties without conducting the proper due diligence. Some lot owners bought their
properties without seeing prior severe flooding events. Whenever there is an
exchange of property, there are two separate issues related to the due diligence of the
buyer and the disclosure of key information from the seller. This may vary if a house
is being sold or just an empty lot is up for sale.
4.3.1 Due Diligence of the Buyer
Whenever coastal property is bought, the buyer should make their own
investigation into the characteristics of a property. Some guidelines for that
investigation come from the following two publications, “Hawaii Coastal Hazard
22
Mitigation Guidebook” and “Purchasing Coastal Real Estate in Hawaii.” The key
issues to look out for are the elevation of the property and the susceptibility to
erosion, flooding, subsidence or other natural hazards. If the potential purchaser does
not know the signs to look out for, they should consider hiring a professional
geologist or coastal engineer to conduct a hazard assessment of the property. In the
22
Available from the University of Hawaii Sea Grant College Program.
45
long run, this may wind up saving the purchaser considerable money. For the Kapoho
area, the key issue to investigate is the susceptibility of the property to high tide
events and how flooding risk may change in the future, if there is ongoing or episodic
subsidence.
4.3.2 Disclosure by the Seller
There are State laws related to the disclosure of material information when a
house is sold. Under the Mandatory Seller Disclosures in Real Estate Transactions
23
Act,
there is a requirement that the seller or seller’s agent disclose all material facts
that would affect the value of the property. Subsidence would be such a material
fact. Unfortunately there are certain gaps in the law, and empty lots without a
structure are not covered. There is anecdotal evidence that empty lots at Kapoho
have been sold to uninformed buyers who later discover the extent of flooding
problems in the area. This is unfortunate because these buyers, with their purchase
create an expectation that they will be able to develop the lots. Whether this
expectation is reasonable or not is another matter.
Because of this serious gap, it is recommended, and the county of Hawaii will
propose strengthening of the disclosure requirements at the county level. This would
be preferable versus trying to amend the State law. Also, a requirement for
disclosure could be put in as a condition for a SMA permit. This would be under the
discretion that the department has in administering the SMA program and following
the objectives and policies in the Hawaii Coastal Zone Management Act related to
24
hazard mitigation.
It is always possible to amend the county SMA rules as a
precaution, but for the disclosure requirement only, this should be in the Department’s
discretion. If however, there are many new provisions that are required related to
subsidence, the SMA rules should be amended.
4.4 Home Construction
This report recommends that both hazard mitigation measures for siting and
construction be employed (Figure 4-1). If construction is to proceed, the issue of
future flooding, wave action, subsidence and earthquakes should be addressed
(Chapter 2). Unfortunately, while many of the hazard mitigation measures for
construction reinforce each other, there are some that don’t. For example, raising a
structure to avoid flood or wave action may make it more prone to damage from
earthquakes. If the structure is raised even higher to account for subsidence, there
will be increased stress on the columns and piers from earthquakes.
All of this needs to be considered, if there is construction. Some of these
issues maybe addressed under the county’s national flood insurance program. Under
23
Hawaii Revised Statutes Section 508D
24
Hawaii Revised Statutes Section 205A
46
this program, the structures near the coast are to be elevated above the 100-year base
flood elevation and construction standards are to address wave action in V zones and
flooding in A zones. The base flood elevations are found on Flood Insurance Rate
Maps or FIRMS. Unfortunately the FIRMS do not take into account subsidence of
the land. If there is subsidence, the hydrodynamics of the coastal area will change
and will put coastal properties at greater risk from coastal flooding and wave action.
This can be compensated somewhat by building higher (i.e., adding freeboard), so
that the property can still withstand the 100-year flood or wave event, even with
future subsidence of the land. The freeboard can be estimated by using a local
subsidence rate and a yearly number appropriate for property (e.g., the life expectancy
of the property).
The requirement to build for wave and flood action under the National Flood
Insurance Program is directed by the Engineering Department within the Department
of Public Works. Building higher with freeboard is not a requirement, but
25
recommended and encouraged under the National Flood Insurance Program. In
order to require freeboard tied to subsidence, it maybe necessary to implement this
requirement through the SMA process and amend the applicable SMA rules. This
would then require action by the Building Department of the Department of Public
Works and not the Engineering Department.
When structures are elevated to account for wave, flooding and subsidence,
they are especially prone to earthquake shaking. As can be seen from Figure 2-2, the
area is very prone to earthquakes. Some measures to deal with elevated piers or
columns and earthquake shaking is to build stronger piers or columns or reinforce
26
them with knee bracing or cross bracing. Some examples of structures with knee
and cross bracing are provided in Figures 4-1 and 4-2.
Indirectly, the requirement to build for earthquake shaking is addressed in the
building code for Hawaii County. In this code, whatever is built must be designed by
a structural engineer to address shaking associated with seismic zone 4. Once the
structure is determined, then a structural engineer would design the structure to
withstand shaking associated with seismic zone 4.
25
In fact a reduction in flood insurance rates is provided for building with freeboard, with greater reduction
for elevating higher.
26
See Chapters 10,11 and 12 of the Federal Emergency Management Agency’s Coastal Construction
Manual.
47
Building Coastal Homes to Resist
Ground Shaking
Knee Braces
Cross Braces
Figure 4-1 – Examples of Coastal Homes with Knee Braces and Cross Braces to strengthen
columns or piers that are needed to elevate houses for flood or wave protection (from FEMA
CCM).
Figure 4-2 – Example of structure in Hilo designed for wave and flood action with modified knee
braces on columns.
48
4.5 Hazard Noticed – Remedial Options Evaluated
Many of the coastal areas at Kapoho have already been constructed without a
full appreciation of all hazards that are subject in the area. Thus this section is
devoted to solutions for existing home and lot owners, as well as those the Hawaii
County Planning Department can help to implement. These measures range from
conventional measures such as increased protection from seawalls to unconventional
measures such as a land swap.
4.5.1 Raising the Height of Existing Seawalls
One issue that the County of Hawaii Planning Department asked to be
addressed was to provide guidance on raising the height of existing seawalls.
During site visits to the Kapoho Beach Lots subdivision, the waves struck very close
to the top of existing seawalls. This is an issue that would be expected with the
indication of active subsidence.
Also from the site visits, the commonly known environmental impact of a
seawall causing a beach to narrow or disappear should not be a concern at Kapoho,
due to the fact that the shoreline is rocky. So the major issue with raising the height
of seawalls has to do with if it is technically feasible.
If there are requests to raise the height of seawalls, this should be accompanied
with a coastal engineering study that indicates it is technically sound. Seawall design
varies, and many seawalls are broad at the base, and taper towards the top (Figure 4-
3). The width of the wall, and the size of the stone are often determined by the height
of the design wave. If the design wave were to change to a greater height, because of
subsidence, it may not be possible with sound engineering principles to just raise the
wall without reinforcing the base. This is outside the scope of the study and it is
recommended that a qualified coastal engineer approve such a change on a case by
case basis.
Many seawalls have a uniform width from the base to the top and are anchored
by an L-shaped arm that is buried at the base in the sand or substrate. For these walls,
the technical hurdles of raising the height may be less, but again it is recommended
that a qualified coastal engineer approve such a change in a report that accompanies
the permit application.
49
Figure 4-3 – Typical Gravity Seawall Design (from United States Army Corps of Engineers -
Pacific Ocean Division) with a broad base and narrow top.
The request for a coastal study to accompany a change in the design or build
of a seawall should be within the County’s current regulatory authority so no new
change in regulations would be anticipated. An important issue is how ongoing and
episodic subsidence are factored into the design. Probably the former can be
addressed by making assumptions on the length of use of the property and a
preliminary subsidence rate. With this report, a local subsidence rate is provided and
can be used until the rate is further refined by future or additional monitoring. More
difficult would be to plan for future episodic events.
4.5.2 Building New Seawalls
There may also be requests for new seawalls in the Kapoho Area. The
analysis for this issue is somewhat similar to that for raising the height of existing
seawalls. The concern about impact to a sandy beach should be of no concern, due to
the rocky shoreline.
One legitimate concern, however, is that any new seawall can divert flooding
of the area to a new location. Due to this potential problem it is recommended that
applications for new seawalls be accompanied by a coastal engineering report that
states that flooding will not be increased elsewhere to the detriment of nearby
property owners. The county Planning Department should have sufficient authority
to requests this study so no new regulations would be required.
50
In the design of the seawall, the potential for subsidence should also be
considered, otherwise there may be future requests to extend the height of the seawall,
after the fact. It would be more efficient and economical to build the wall to the
correct design height initially, than to attempt to modify the design at a later date. For
both this section and 4.5.1, the county should balance the important need for the
homeowner to protect themselves, with the risk of hazards as discussed in Chapter 2
of this report.
4.5.3 Legal Status of Existing Seawalls
The Hawaii County Planning Department asked that this report help determine
the legal status of the seawalls for the Beach Lots and Vacationland subdivisions. A
review of the files did not allow a determination of which lots had seawalls which
were legally permitted. For most of the files, there was no determination. On
November 29, 1983, a complaint was made to the Planning Department by then
Hawaii County Civil Defense Director Harry Kim regarding several properties in the
Beach Lots and Vacationland subdivisions for an apparent violation of the shoreline
setback law. The complaint called for further investigation of at least 31 properties.
For many of these properties, this complaint is the only information in the folder and
thus the question if the seawalls were properly permitted cannot be determined by the
files alone, since the results of any other investigation of the structures that may have
been done are not known.
Seawalls built before June 22, 1970, the effective date of the applicable
shoreline setback rules, are grand fathered in and deemed to be legal. An
investigation was made at the R.M. Towill Company for aerial photographs that
existed in the area for the period from 1965 to 1975. A 1977 aerial photograph was
identified and then blown up 8 times to determine if there were existing walls at that
time. Generally, the high altitude of the aerial photograph did not allow a
determination if there were seawalls for most of the properties. For two of the west
lots makai of Waiopae Road, existing walls were identified in 1977. If these
seawalls existed before 1970, they would be legally existing walls. Although it could
be surmised that the close proximity in time between 1977 and 1970 makes it likely
that these walls existed beforehand, this cannot be certain since there could have been
many activities along the shoreline after the 1975 Kalapana earthquake.
4.5.4 Land Exchange
In studying the Kapoho area, both in the field and from existing reports, two
observations stand out. First the area is very susceptible to natural hazards (Chapter
2). It would be hard to find a coastal area in the State of Hawaii that has greater risk.
The area is at risk not only from slow ongoing processes, but major catastrophic
events. Problems from a hazard mitigation standpoint and administrative standpoint
are compounded because subsidence has allowed the development in the area to
interfinger with the ocean.
51
Equally striking from the site visits is the beauty of the area, specifically the
tidal pools, clear water and suitability of the area as a Marine Life Conservation
District, of which there is currently one on site.
While it was outside the scope of this report to work out the details of a land
exchange, such an option should be investigated. One option of many is to obtain an
appropriation from the legislature to study the feasibility and work the details of a
land swap. This appropriation could be similar to the one passed in the 2006
legislative session which provided funds to study wastewater issues. However it is
felt that deciding the future long term course for Kapoho should be just as important.
The land exchange concept was very briefly mentioned in the October 19,
2006 community meeting. It was an option briefly commented on by a few
attendees. They were in favor of this option and asked that it be addressed, but
skeptical. This is understandable given the tremendous complexities associated with
this option.
With regard to a land exchange, a few points require clarification. Raising this
option should not be implied or indicate that the State or county have a duty to pay
compensation for properties at risk, or currently subject to wave action or flooding.
Conceivably the State or county could take a hard approach under their considerable
police power to protect life and property from natural disasters. However, the land
exchange is an option that could be used to facilitate and expedite moving residents
out of harms way before the area experiences a major hurricane, tsunami or episodic
earthquake event with subsidence.
A land exchange could be, or should be purely voluntary with the landowner
having the option to keep their property, or exchange it for other areas that are inland.
The incentive for the landowner to move would be if the regulatory scheme for
inundated properties eventually resulted in not being able to build on the property at
all. For example, a potential impasse may exist for some of the makai lots because of
the extensive flooding on some of the properties. Yet the State is unlikely to claim
land that is submerged. Part of this is due to the anomalous results possible given the
topography on some of the lots (Figure 4-4). This topography could result in different
portions of the same lot having different ownership status. If the State does not claim
ownership of the lots, then they would remain as private property. Yet they may not
be able to be built without a shoreline certification, or a SMA permit or a
Conservation District Use Application permit, which maybe very difficult. This
illustrates the impasse that exists for certain lot owners’ makai of Waiopae Road. A
land exchange at either the State or county level could remove problem properties
from this current limbo.
52
Figure 4-4 – On some makai lots at Kapoho, the land is submerged during extreme high tides, but
the State is unlikely to make a claim for ownership of the land. One reason is that the natural
topography on the lot results in portions being submerged while other parts or “islets” are dry and
theoretically remain private property. It would be unlikely that the State would claim such land
when there could be different ownership status for specific portions on the same lot. The land
while the possibility of building on it through a SMA or CDUA
may remain private property
permit would be difficult.
Because of the potential impasse due to flooding, the State or county need not
offer prime coastal real estate in exchange, but instead land of reasonable value that
can be used as an incentive to move away from a hazard prone area. In considering
the fairness of the exchange, the value of a particular Kapoho parcel in question
should factor in its susceptibility and frequency to flooding, both in the present and
the future.
Finally, if a land exchange ever materialized, a possible strategy would be to
target those properties that currently have the most severe flooding problem or are at a
certain stage of development (e.g., empty lots that are about to be built on, or severely
flooded existing homes). These would be some of the issues that could be addressed
if the feasibility of the land swap concept were evaluated.
In considering some type of land exchange, the process that was utilized to
move displaced residents in the Puna District from land that was destroyed by lava
should be considered as one of many options. For example, the Kikala-Keokea
subdivision was created and leased to Kalapana residents displaced by lava flows.
53
4.5.5 Land Acquisition
Another option from the land exchange, and one that maybe quicker to
implement is to acquire certain problem properties. This acquisition can be offered
as a voluntary incentive for the landowner to move from harms way. The history of
flooding and the susceptibility to future events should be considered in calculating a
fair amount to offer.
At the time of completion of this report, a meeting was held with Senator
Russell Kokubun, the originator of Senate Bill 2480 which commissioned the study of
wastewater issues at Kapoho (see Appendix 2). The purpose was be to explore
alternatives for Kapoho at the State level similar to those covered in Sections 4.5.4
and 4.5.5. Since the Legislature was instrumental in commissioning the study of
wastewater problems at Kapoho, they could eventually be involved in initiating a
study on the long-term solutions of the Kapoho area. This would have to be further
explored.
From these discussions, it was indicated that the DLNR and Board of Land
and Natural Resources (BLNR) have the primary responsibility with respect to
shoreline issues, subsidence and mitigating these impacts. Therefore an appropriate
strategy would be that after landowners become informed of the facts of the
surrounding subsidence, they could inquire with the DLNR and BLNR regarding
appropriate options. It would be up to the DLNR/BLNR to investigate these requests
and explore alternatives. One of the options could be to seek more resources from the
legislature to gain more information, or propose a land exchange or land acquisition.
Another alternative proposed by Senator Kokubun was to have a third party
intervene such as the Nature Conservancy or Trust for Public Lands. These
organizations could possibly purchase properties with a high natural resource value
and in doing so, provide tax relief to the sellers. Subsequently, the state, county or
federal government can then purchase these lands for park or other similar uses.
54
Chapter 5 – Conclusion and Summary
If subsidence continues at Kapoho, over time the area will become more
vulnerable to events such as a major, or even a minor tsunami, hurricane or tropical
storm. In addition, the area is subject to earthquake risk and associated shaking,
potential major subsidence and a local tsunami. Unfortunately, the three major
hazards (hurricane, tsunami and earthquake) are relatively independent and from past
historical frequency, likely to occur in a persons lifetime.
From the research conducted for this report, the following key points are
provided:
1)Based on InSAR studies conducted at the University of Hawaii, the relative
sea level rise for Kapoho has been estimated to be ~0.8 to 1.7 cm/yr+/- 0.8
cm/yr (2 standard deviations) over the last three years. This figure is in
agreement with separate GPS measurements taken for nearby areas by the
Hawaii Volcano Observatory.
2)The Kapoho area has a history of ongoing slow subsidence and more rapid
subsidence associated with major earthquakes (1823, 1868 and 1975).
3)It is recommended that the area continue to be monitored with InSAR,
satellite GPS and tide gauges. The relationship between ongoing subsidence
and episodic subsidence is not well known. In addition, continued
monitoring will allow further refinement in the measurement for any
subsidence.
4)The subsidence in the past has allowed the ocean at Kapoho to interfinger
with existing development. This complicates development decisions and
makes existing development more vulnerable to hazards such as storms,
hurricanes and tsunamis.
5)The Kapoho area is at high risk from hurricanes and tsunamis (distant and
local). Because of the low elevation from the subsidence, the vulnerability
from major as well as minor events such as storms increases.
6)This report recommends that hazard mitigation issues be given serious
consideration during all stages of development for the area.
7)Some of the complications with shoreline certification in the past will be
alleviated now that the State has changed policy and agreed to conduct
certifications in the Kapoho area.
55
8)Based on the recent Supreme Court decision, it is recommended that all
evidence be used to determine the shoreline (“upper reach of the wash of the
waves”), including debris lines, specific types of vegetation that are not salt
tolerant and observations of inundation based on high tide events (surface
connection).
9)Observations on inundation based on surface connection are a valid
approximation to determine the shoreline. However this method may
underestimate the upper reaches of the wash of the waves because of: (i)
tides higher than 2.8 above MLLW, and (ii) wave and wind setup that may
cause the inundation for lesser tides to exceed higher tides. Nevertheless,
most wave action is depth limited.
10) Inundation based on gravity flow could conceivably be excluded from the
determination of the shoreline. Although this should be within the State’s
discretion, if a rule change is sought by the State, this would delay this
option.
11)Excluding gravity flow would facilitate development in some areas, but
would expose these developments to increased flooding if ongoing
subsidence continues.
12) Since subsidence is active, care should be taken not to change the shoreline
certification process in a way that increases exposure of inhabitants and
residences to actively flooding areas.
13) Based on site visits, there are three to four distinct areas where the water
breaches Waiopae Road during high tide. From site visits and interviews,
the extent of inundation appears to be affected by wind and wave setup.
14) Hazard mitigation measures for Kapoho should include those for siting and
construction.
15) For siting, a hazard assessment that factors in subsidence should be
conducted for new zoning, general and community planning amendments
and subdivisions at Kapoho and adjacent areas. This will allow better
planning of the area for future hazard risk and greater protection to future
inhabitants. Siting measures such as a setback should be given equal, if not
greater consideration over a rolling easement, especially in these early stages
of developments.
16) In the case of an existing lot that floods, development of a new house should
be discouraged, but if it occurs, the proper measures should be employed
(flood and wave construction, flood insurance, freeboard, earthquake
56
reinforcing, and disclosure of hazard risks). Implementation of the rolling
easement concept should be considered for new houses on existing lots.
17) Because of subsidence, freeboard should be added to piers and columns.
Under the National Flood Insurance Program, the freeboard is not mandatory
but incentive based with discounts provided in insurance for extra elevation.
18) The requirement for freeboard may require an amendment to the county
SMA regulations. If amendments are made, the requirement for adequate
disclosure during a lot transfer or home transfer should also be included.
19) Consideration should be given to sending a request to FEMA to modify
their flood insurance maps based on subsidence. This would require a letter
of map revision.
20) If structures are elevated with freeboard because of subsidence, the design
should account for shaking as required under the building code, which
requires structures to be built to Seismic Zone 4. Strengthening of columns
and piers, as well as knee or cross bracing may be required.
21) The county and State should work on a voluntary program of land exchange,
and or acquisition to expedite and encourage moving residents or potential
residents out of harms way. When the risk of future disasters are considered,
the cost for such a program could be very cost effective.
22) The wastewater study commissioned by the State legislature for Kapoho
should factor in subsidence.
23) Requests for new seawalls or to extend the height of existing seawalls
should be accompanied with a coastal engineering study.
To facilitate the implementation of hazard mitigation measures, a program
for land exchange or acquisition of property should be investigated by the State,
county and landowners. Eventually, the State DLNR/BLNR could seek resources
from the Legislature regarding additional investigation on the mechanics of a land
exchange or acquisition program, or actual implementation of a program.
Acquisition of property can also be initiated by organizations such as the Trust for
Public Lands and the Nature Conservancy.
57
Appendix 1 - Summary and Analysis of Relevant Studies
Applicable or For the Study Area
Federal Emergency Management Agency. 2000. Coastal Construction Manual –
Principles and Practices of Planning, Siting, Designing, Constructing, and Maintaining
Residential Buildings in Coastal Areas, Vols. 1-3.
The Coastal Construction Manual provides measures to reduce the risk
from all coastal hazards during the construction stage, and partly
through siting. Many measures in the CCM are used in this report.
Fletcher, C.H. and Hwang, D.J. 1994. Shoreline Certification Review and
Recommendations, Office of State Planning – Coastal Zone Management Program, p.
76.
This report reviews the shoreline certification process in Hawaii and
makes several recommendations; the primary one is to use an increased
emphasis on the vegetation line during shoreline certifications. This
recommendation is discussed in this report.
Fletcher, C.H., Grossman, E.E., Richmond, and B.M., Gibbs, A.E. 2002. Atlas of
Natural Hazards in the Hawaiian Coastal Zone, U.S. Department of the Interior, U.S.
Geological Survey, University of Hawaii, State of Hawaii Office of Planning, National
Oceanic and Atmospheric Administration, p. 182.
The Atlas creates a risk ranking scheme for all coastal areas in Hawaii
based on the risk from tsunamis, stream flooding, high waves, erosion,
sea-level rise, and volcanic-seismic activity. These risk maps are used
in this report to provide a preliminary estimate of the hazard risk in the
Kapoho area. This Atlas should be used as a preliminary guide to
assess hazard risk for new development along the coast.
Hwang, D.J. 2005. Hawaii Coastal Hazard Mitigation Guidebook. Prepared for the
Office of Conservation and Coastal Lands, Department of Land and Natural Resources;
Coastal Zone Management Program – Office of Planning; University of Hawaii Sea
Grant College Program; and the Pacific Services Center and Coastal Services Center of
the National Oceanic and Atmospheric Administration, p. 216.
This report identifies coastal hazards of concern in Hawaii, develops a
multi-hazard zonation scheme and recommends hazard mitigation
measures for construction and siting based on the stage of development.
These concepts are applied in this report. It is recommended that this
report be utilized in future development decisions along the coastline.
Hawaii Community Foundation, Vacationland Hawaii Community Association, Kapoho-
Kai Water Association, University of Hawaii-Hilo, State of Hawaii Department of Land
and Natural Resources. Kapoho Reef Watch – Annual Report One – Summer 2004 –
Featuring Human Use Surveys, Water Quality Monitoring, Biological Monitoring of
58
Fish, Algae and Invertebrates; Water Quality Restoration – at the Waiopae Tide Pools
Marine Life Conservation District and Control Area.
There were many important findings in the Kapoho Reef Watch study.
In terms of visitors, approximately 46,000 visitors were counted using
the tide pools during the year one study. The busy times were from
May to August. There was on average about 3.4 people per parked car
and about 12,820 cars. With regard to water quality, Enterococci
bacteria (EC) exceeded acceptable safe levels in many of the tide pools
as define by the State Department of Health and the EPA. Cesspool
leaching is the most likely contributor of EC to the tide pools.
State of Hawaii, Department of Land and Natural Resources. 2005. Requesting a Review
and Analysis of the Issues Surrounding the Shoreline Certification Process for the
Purpose of Establishing Shoreline Setbacks. Report to the Twenty-Third Legislature
Regular Session of 2006 in Response to Senate Concurrent Resolution 51, Senate Draft 1
– Regular Session of 2005.
This report makes short-term and long-term recommendations to
change the shoreline certification process. The two most notable areas
are to change the state administrative rules definition of the shoreline to
match that in the Hawaii Revised Statutes. This would then place a
more equal weighting on evidence for the shoreline on both the debris
line and vegetation line. More relevant to this study is the long-term
recommendation to replace “upper reach of the wash of the waves,”
with “run-up,” and to exclude from this definition inundation aided by
gravity flow or funneling through narrow passages. This
recommendation, or a permutation of it is presented in this report as an
option.
59
Appendix 2 - Summary and Analysis of Interviews, Meetings
or Site Visits with Affected Stakeholder and Agencies
August 3, 2005 – Interview with John Green – landowner in the Kapoho
Vacationlands Subdivision. Major concern for the landowner is being able to build
after buying the lot. When he visited the property, he did not see the property at a
high tide. He was not informed of need for a shoreline survey. The need for a
shoreline survey is preventing him from building on the property. He gave approval
to go on site.
August 17. 2005 – Field observations at the Kapoho Vacationland Subdivision with
Dr. Ben Brooks, Dr. James Foster, Chris Conger, Larry Brown, Eric Schott and
Dennis Hwang. Observe the 3.1 high tide at the Vacationland Subdivision. Six
station areas are established to observe the extent of inundation. Measure inundation
limits for accessible areas with the use of high resolution satellite GPS units.
October 14, 2005 – Interview with Chris Yuen – Director of the Department of
Planning – County of Hawaii - Discussed the theory of land swaps and the need for
more work in this area. Possibilities and hurdles were discussed at the county and
State level.
January 9, 2006 – Meeting with Chris Conger, Reid Siarot, Dolan Eversole Morris
Atta and Sam Lemmo at the DLNR office. Discuss the shoreline certification
process and the field observations at Kapoho from the August 17, 2005 field survey.
Discussion about participation in the February 8, 2006 community event for Kapoho.
February 8, 2006 – Meeting at the Hawaii Volcano Observatory with volcanologist
Don Swanson, Asta Mikilius, Paul Okubo, and Hawaii County Planner Larry Brown.
Discuss the history of volcanoes and subsidence in the areas. Measurements taken by
field surveys on subsidence rates is provided for a nearby area. An explanation is
provided of a previous letter to the Hawaii County Planning Department by Don
Swanson on measured subsidence in the area. A report is given on the cause and
distribution of earthquakes and subsidence in the area.
February 8, 2006 – Meeting at the Pahoa Community Center to give a regulatory
review of issues to the residents of Kapoho. Present at the community meeting were
the Department of Health, Army Corps of Engineers, Department of Land and Natural
Resources, Hawaii County Department of Planning and Dennis Hwang. PowerPoint
Presentations were given by the participants. Questions were raised to the panelists
and answers provided. A brief review of the findings during the August 17, 2005 site
visit were provided. The residents were then informed that the InSAR study was
being conducted to measure subsidence, but no detailed results were out yet. An offer
was made to meet any resident that wanted to discuss the Kapoho area and any
individual concerns during a site visit to the area during the next morning.
60
February 9, 2006 – Interview with residents of Kapoho that wished to discuss
th
individual concerns and issues. Invitation made at the February 8 community
meeting to anyone interested in meeting. Meet with Linda and Kirk Flanders and
discussed coastal vegetation suitable for use as a shoreline indicator, the reef structure
and history of the area.
July 12, 2006 – Status report with Hawaii County Planning. Present were Director -
Christopher Yuen, Deputy Director Brad Kurakawa and county planner Larry Brown.
The justification for obtaining an extension for the Kapoho study was provided. The
main reason being the need to expand the time range of the InSAR data to get a better
handle on potential subsidence. The concern for potential ongoing subsidence was
raised. A status report was given on the expected timetable for products, preliminary
findings, and a site visit. Preliminary maps of the inundation event of August 17,
2005 were shown for form and content. Discussion followed on the issue of raising
the road.
July 12, 2006 – Field Survey at the Kapoho Vacationland Subdivision. Present Dr.
James Foster, Larry Brown, Shanna Dacanay and Dennis Hwang. Observe the 3.13
high tide predicted from the NOAA tide charts. See if there are any changes in the
extent of inundation, compared to a similar 3.17 high tide event on August 17, 2005.
Measure and observe channels crossing the road for depth and possible transition
from runup to gravity flow.
July 31, 2006 – Interview with Harold Yee of the Department of Health, head of the
Wastewater Branch. Of the three general systems for wastewater collection at
Kapoho, cesspool, septic tank and a sewer or community wastewater collection
system, the later should have the least technical challenges. Both the cesspool and
the septic tank could have a hard time with proper flushing if they are close to the
water level. Mr. Yee indicated that an appropriation to study wastewater issues at
Kapoho was approved at the State legislature.
August 2, 2006 – Interview with Eric Schott, homeowner at Kapoho Vacationland
Subdivision. Senate Bill 2480 was approved by the State legislature to study
wastewater options for both the Kapoho Vacationland and Beach Lots area. At the
time of the discussion, the money had not yet been released by the Governor. Also
tropical storm Daniel went by the Hawaiian Islands on July 28 and the water level at
Kapoho was much higher than the highest tides. On the road, the water may have
been a foot higher, even though the tide was only 2.5 as indicated by the Old Farmers
Almanac and the NOAA tide charts. This should not have implications in terms of
shoreline certification since storm waves are exempt, yet it indicates how vulnerable
the area is to storm events.
61
October 19, 2006 – Community meeting at Pahoa High School – The main purpose of
the meeting was to inform the public, and the residents of Kapoho, of the results of
the INSAR study and to discuss preliminary direction of the Subsidence Report.
Dr. Benjamin Brooks showed a PowerPoint on the concepts behind INSAR. He
compared the results of the study with independent measurements from high
resolution GPS taken by the Hawaii Volcano Observatory. The match was very good
for the existing two locations. Measurements taken by INSAR over a three-year
period indicate subsidence relative to Hilo at about 1 cm or 10 mm per year. Since
Hilo is experiencing relative sea level rise of 2 mm per year, the relative sea-level rise
measurements over the three-year period of study gives a rate of about 1.1 cm or 11
mm per year at Kapoho. This is consistent with the 30-year trend revealed by
independent measurements taken by the Hawaii Volcano Observatory.
Dennis Hwang gave a PowerPoint that covered preliminary direction of the three
major areas of the report. With regard to risks of hazards, the area is very vulnerable
to hurricanes, tsunamis, and earthquakes. Subsidence makes mitigation of these risks
even more difficult. Subsidence appears to be both episodic (1838, 1868, and 1975
events) and continuous (INSAR study). The second major area of the report dealt
with options to deal with the shoreline certification process. Four options were
considered including: (i) using the existing method of surface connection, (ii)
encouraging the State to rely on an increased emphasis of the vegetation line, (iii)
using the transition to gravity flow and (iv) setting an arbitrary boundary such as the
mauka edge of the road. Options iii through iv would provide the county greater
flexibility in granting building permits but the down side is that this could increase
development pressure in the areas of severe flooding and subsidence. The third
major part of the study dealt with various issues in the Special Management Area. It
was suggested that: (i) the area continue to be monitored for subsidence, (ii) an
engineering report accompany applications for new seawalls or to heighten existing
seawalls; (iii) zoning and subdivision changes factor in flooding and subsidence; (iv)
the wastewater study to be done under legislative appropriation consider subsidence.
There was much discussion about building a new house on existing lots and
developing the right strategy, considering the frustration felt by landowners as well as
the hazard risks. If new houses are built, it was suggested there be sufficient
elevation, with freeboard for subsidence and that the structure can also accommodate
anticipated earthquake forces.
62
December 18, 2006 to January 25, 2007 – Discussions with Senator Russell Kokubun
regarding possible solutions at the Kapoho area. Options were discussed regarding a
follow up long term study, land exchange and land acquisition. It was suggested that
an appropriate course of action would be for the landowner or community to become
knowledgeable about the issues at the area. They could then inquire with the DLNR
and Board of Land and Natural Resources (BLNR) regarding solutions. The
DLNR/BLNR could then investigate and propose resolutions which could include
seeking resources from the Legislature to gain more information or initiate a land
exchange or acquisition.
63
Appendix A – Measuring Ground Motion and Estimating
Relative Sea Level Change at Kapoho, Hawai’i Using Synthetic
Aperture Radar Interferometry (InSAR) by Dr. Benjamin A.
Brooks, Christin Shacat and Dr. James Foster
64
Measuring Ground Motion and Estimating Relative Sea Level Change at
Kapoho, Hawai`i Using Synthetic Aperture Radar Interferometry
(InSAR)
A report prepared by
Contact information: Pacific GPS Facility
School of Ocean and Earth Science and Technology
University of Hawaii
1680 East-West Rd.
Honolulu, HI 96822
bbrooks@soest.hawaii.edu
25 November, 2006
1
Executive Summary
To gather more information about the state of current land motio
Kapoho region, the Pacific GPS Facility was contacted by Dennis
Reinwald O'Connor & Playdon to carry out a study in the region u
Radar Interferometry (InSAR) techniques.
After an initial search, we determined that data from the WINSAR archive
(http://winsar.stanford.edu/main.php) , of which the University of Hawai`i is a member,
covered the Kapoho region from February 2003 to July 2005 at close to monthly intervals.
As we processed the data and realized that we were getting interpretable results, we
requested and received an extension to process ~ 6 months worth
resulting in a total time span of February 12, 2003 to March 8, 2006.
The results indicate that the immediate Kapoho region experienced average downward
vertical motions, with respect to Hilo, of ~-0.7 to -1.6 ± 0.6 (2 standard deviations) cm/yr
for the three years of data processed. Our InSAR results are in very good agreement with
GPS and leveling results collected by the Hawaiian Volcano Obser
study neither addresses the cause of the measured land motion, n
behavior. The measured land motion is an order of magnitude larg
decadal sea-level increase in the Hawaiian Islands (Caccamise et al., 2005) and so it appears
that local land motion exerts the dominant control on relative sea-level change in Kapoho
which we determine to be ~ 0.8 to 1.7 ± 0.8 (2 standard deviations) cm/yr.
Additionally, we carried out repeat GPS surveys of the high-tide
on in August, 2005 and June, 2006. We note specifically here tha
differences in the high-tide position observed on the different
interpret these differences nor to suggest their causative facto
-4
from the first survey to be 3.5x10 degrees.
2
Introduction
Measuring Sea Level Change
Mitigating the effects of sea level rise is a major societal c
Recent satellite altimeter observations indicate that the rate of global sea level (GSL) rise is
~3 mm/yr since the mid-1990s (Leuliette et al., 2004), an increase above the 1-2 mm/yr
20th century rate determined from tide gauges (see summary in (Church et al., 2001)). This
apparent acceleration heightens concerns not only of the pace of shoreline encroachment,
but also of the damaging impacts of extreme water level events associated with high waves
and storms that are expected to increase as coastal sea levels rise. Accurate assessment of
sea level rates therefore is an important concern for coastal ma
concerned with the protection of lives and property along the coast.
Local determination of the rate of change of relative sea level
relative to the adjacent land, is likely to differ considerably
referenced ideally to the earthÔs center of mass or geoid. This is due in part to ocean
variability, which leads to decadal and longer period fluctuations that dominate RSL rates at
these time scales (Douglas, 2001). Even if sufficient data are available to differentiate secular
trends from ocean variability, vertical land motion (VLM) can contribute to RSL trends at a
level comparable to the ocean. A prominent contributor to VLM i
continents associated with the reduction in land ice mass following the last ice age, or post-
glacial rebound (PGR). RSL measured along many high latitude co
(Woodworth, 1990) and direct GPS measurements have been used to
contribution (Scherneck et al., 2001). PGR is a geologic time scale phenomenon that
appears as a secular trend component in tide gauge observations. Models have been
developed to estimate PGR rates (Tushingham and Peltier, 1991),
primarily for high latitude locations.
At mid- to low-latitudes, other processes tend to dominate the coastal VLM signals. Local
deformations due to ground water or oil extraction, the settling of landfill, earthquakes, and
other volcanic or tectonic effects are likely to have short spatial scales and nonlinear and
abrupt behavior in time; consequently they are much more difficult to model than PGR. A
single VLM measurement at an unstable location is unlikely to represent motion over a
larger area, unlike a PGR-dominated site.
Continuous GPS (CGPS) measurements at tide gauges and/or tide ga
provides a means of correcting for VLM signals in sea level records (Bevis et al., 2002;
Mitchum, 1998). This allows for an estimate of VLM at the tide gauge, but not of the
surrounding region. Dense CGPS networks such as the Southern California Integrated GPS
Network (SCIGN) can provide information on regional relative gro
even a network as extensive as SCIGN is essentially a collection of point measurements that
are sparse relative to VLM spatial scales and along the coast wh
determining RSL .
In a recent publication of ours (Brooks et al., In Press) we demonstrated how the emerging
technique of satellite-based InSAR (Burgmann et al., 2000) combined with traditional tide
3
gauge observations, could provide RSL estimates for a coastal re
spatial resolution. For the Los Angeles basin region we produced a map of VLM rates from
1992-2000 with horizontal resolution of 20 meters and vertical r
millimeters. The map allowed us to estimate VLM in the immediate vicinity of a centrally
located tide gauge and yielded a regional assessment of RSL for two continuous coastal strips
of ~15 and 45km length.
Synthetic Aperture Radar Interferometry (InSAR)
Applying InSAR for space-based deformation mapping of sub-cm scale ground motions is
now an accepted technique worldwide and it has been reviewed extensively by other authors
to which we refer readers for an in-depth explanation (Burgmann et al., 2000; Hanssen,
2001; Rosen et al., 2000). For the purposes of this report, we give a brief review here.
There are currently a number of satellite platforms which provid
), the Canadian
European Space AgencyÔs ERS-2 and Envisat (http://earth.esa.int/
Space AgencyÔs Radarsat (http://www.space.gc.ca/asc/eng/satellites/radarsat1/default.asp),
and the Japanese Aerospace Exploration AgencyÔs recently launched ALOS
(http://www.jaxa.jp/missions/projects/sat/eos/alos/index_e.html)
Envisat. Envisat is in a sun-synchronous polar orbit with a mean altitude of 800 km and a
35 day repeat time.
InSAR uses radar images acquired from repeat satellite orbits (e
descending) to measure the range change along the radarÔs line-of-sight (LOS) by interfering
and phase-differencing of time-separated images and removal of the topographic phase with
a digital elevation model (DEM). Envisat can acquire SAR data in 7 different imaging
modes, each with different LOS; here we used image mode 2 with a LOS of ~19-27º from
vertical. The high angle of incidence means that the LOS range-change values are most
sensitive to vertical changes. When only either ascending or descending data are used there is
a fundamental non-uniqueness between LOS range change and vertic
additional data are needed to asses the horizontal contribution of motion to LOS range
change. In this study we used descending data only. For the Kapo
there is a negligible effect of horizontal motion on range change because horizontal GPS
velocities from the Kapoho region are not different than zero at
(Miklius et al., 2005).
The InSAR technique is limited by the degree of interferometric coherence for targets on the
ground between acquisitions. In addition to temporal (Rosen et al., 2000; Zebker and Villas
nor, 1992) and seasonal decorrelation (Lu and Freymueller, 1998; Wicks et al., 1998),
geometrical baseline decorrelation for distributed scattering targets is proportional to the
component of the baseline perpendicular to the line of sight. Because the combination of
path length difference along the line of sight due to deformation, variations in atmospheric
path delay, and noise generally exceed half a wavelength, the interferometric phase must be
unwrapped to resolve spatial and temporal ambiguities (Goldstein
Geodetically Measured Subsidence History of Kapoho
Because of its proximity to Kilauea VolcanoÔs lower east rift zone, ground motion near
th
Kapoho has been monitored over the last half of the 20 century by a combination of
geodetic methods including leveling and GPS (Delaney et al., 1998). The largest individual
4
signal was due to the M 7.2 Nov. 29, 1975 Kalapana earthquake wh
~30km southwest of Kapoho (Lipman et al., 1985). This event, the largest Hawai`i
earthquake in over a century, produced between 20 and 30 cm of s
(Lipman et al., 1985). Since the time of the Kalapana earthquake and 1996, repeated surveys
showed that point measurements from KilaueaÔs lower east rift zone near Kapoho averaged
1-2 cm/yr. of subsidence between 1976 and1996 (Delaney et al., 1
Data, Processing, & Results
From the WInSAR archive we acquired a total of 21 descending E
were in image mode IS2 and in track 429, frame 3213. Table 1, below, lists the data and
shows perpendicular baseline differences with respect to the Dec
# Orbit Date Bperp (m)
T (days)
1 4992 20030212-585.82-665
2 6996 20030702-77.77-525
3 7998 20030910496.21-455
4 8499 20031015650.98-420
5 9000 20031119-736.15-385
6 9501 20031224570.67-350
7 10002 20040128563.72-315
8 10503 20040303-142.25-280
9 11505 20040512-374.64-210
10 12006 20040616274.74-175
11 12507 20040721385.02-140
12 13509 20040929-108.91-70
13 14010 20041103339.24-35
*14 14511 200412080.000
15 15012 20050112-201.2535
16 16515 20050427909.07140
17 18519 20050914529.58280
18 19020 20051019410.01315
19 19521 20051123178.26350
20 20022 20051228-103.83385
21 21024 20060308-165.95455
Envisat scene list. Data are all descending pass, image mode IS2, track 429, frame 3213. #, identification number;
Orbit, orbit reference number; Date, acquisition date (yyyymmdd); Bperp, perpendicular baseline with respect to December 8, 2004
scene;
T, time difference with respect to December 8, 2004 scene.
We used GAMMA software (Werner et al., 2000) to process the data from the raw radar
echoes to the final deformation rate map. Our creation of interferograms is straightforward
and follows established practice (Werner et al., 2000) including
interferogram using a minimum cost flow algorithm (Chen and Zebker, 2000). Additionally,
we refined baseline estimates by minimizing in a least-squares sense the deviations between
observed and model assuming that baseline errors cause long spatial wavelength phase errors
that are linearly dependent on the distance between points.
5
From the 21 scenes acquired, a total of 210 separate pairs could
interferograms. We inspected each of these individually and foun
with perpendicular baselines greater than 300 meters started to exhibit slight degradation of
coherent phase in some areas of interest, notably Hilo. Accordi
analysis to only those interferograms made with pairs separated by perpendicular baselines of
less than 300 meters. Our resulting data set then comprised 71 total interferograms and, of
these, 8 interferograms could be formed from entirely independen
experience with InSAR and meteorology (Foster et al., 2006; Foster et al., 2003) has shown
us that there can be high levels of atmospheric water vapor at any given time over in
Hawai`i. Thus, for a data set of only 8 interferograms, an analy
biased if only 1 or 2 scenes contained significant atmospheric anomalies, especially if those
scenes covered the longer temporal baselines most important for determining LOS range
change. As a result, we prefer to analyze the data set of 71 interferograms rather than 8, even
though the larger data set does include some redundant informati
being used more than once to form interferograms.
We calculated average LOS range change by estimating in a least-
pixel with coherent signal in each of the images, a linear defor
of phase versus time). This technique is often referred to in t
is regarded as an effective means of removing atmospheric water vapor anomalies which
may degrade a data set (Sandwell and Price, 1998). Because atmospheric anomalies are
typically not correlated over the monthly time intervals of this data set, a linear regression
will be an effective means of removing the atmospheric signal from the resultant land
motion map.
In Figure A.1, we show a map of the average range change rate from the full data set of 71
interferograms for the entire processed scene. In this analysis,
sea-level change, all values are reported with respect to a reference point at the Hilo airport
which is very near the Hilo GPS station. Notable features of the deformation map include
the well-studied deformation associated with Kilauea volcano. In
zoom of the results from the Kapoho area in addition to the standard deviation of the range
change rate for each pixel. Generally it appears that Kapoho LOS
from between ~ -0.8 to -1.7cm/yr with standard deviations uniformly in the ~ -3mm/yr
range (Figure A.2b). A more conservative error estimate of two standard deviations would
yield values of ~ -6mm/yr.
Our InSAR results are in very good agreement with GPS and leveling results collected by the
Hawaiian Volcano Observatory since 1975. As mentioned above, and shown in Figure A.4,
sites from KilaueaÔs lower east rift zone near Kapoho averaged 1-2 cm/yr. of subsidence
between 1976 and1996 (Delaney et al., 1998).
Error Analysis
Data Decimation
We assess the robustness of our result empirically by repeatedly decimating the data stack
and re-running the linear regression. In Figure A.3.1 we show the results of 14 different
6
iterations of the decimation process which comprises randomly decimating the data stack by
5 scenes each time. From a total of 71 to a total of 26 scenes the results are similar in that
over the entire Kapoho region values of LOS range change with re
between ~ -0.8cm/yr to ~-1.7cm/yr or ~ -0.7 to -1.6cm/yr when projected onto the vertical
(as discussed above, horizontal motion in Kapoho from GPS is essentially negligible).
7
8
9
10
11
Correspondingly standard deviation of displacement rate ranges
0.7cm/yr as the number of scenes in the stack decrease from 71 to 26 (Figure A.3.2). This
increase in result variability with fewer scenes is to be expected and is due to the increasing
probability of atmospheric anomalies influencing the result when
interferograms are used.
As a result we find that average vertical motion of the Kapoho r
studied was between -0.7 and -1.6cm ± 0.6 cm/yr (2 standard deviations). This result is in
excellent agreement with the independent leveling and GPS results reported by Delaney et
al. (1998) who found subsidence rates on the order of 1-2 cm/yr (Figure A.4).
Consideration of Lava Flow Cooling
It is clear from the deformation maps (Figure A.2) that the zones of coherence where we can
achieve reliable land motion estimates are the 1955 and 1960 lava flows, respectively (Richter
et al., 1970; Trusdell et al., 2005). Because the principal area of interest, the Kapoho
vacationland lots, are not situated on the flows themselves it i
emplaced flows may be still experiencing some cooling and so ref
motion than that actually experienced ~100-200 meters away at Kapoho vacationland lots.
We find this scenario highly improbable for the following reason
1)Neither flow exhibits a spatial patterns that we would expect fr
as greater subsidence towards the central (and presumably thicke
flows.
2)Numerical models of lava flow emplacement (e.g. Patrick et al., 2004) suggest that it
is highly unlikely that, more than 40 years after their emplacement, the lavas would
still retain any molten material. Patrick et al. (2004) showed u
different cooling models (validated with observational data) that an initially 100m
thick lava flow would be entirely solid by less than 35 years. Because of the cooling
effects of cracks and water percolation it is likely that these are upper-end estimates
for solidification rates. Moreover, Richter et al. (1970) showed
from the 1960 vents that the flow thickness does not exceed ~ 30
thick flow would cool significantly faster than the 100m thick f
Patrick et. al (2004) we conclude it is highly improbable that the 1955 and 1960 flows
are still cooling.
Estimating Relative Sea Level Change for Kapoho
Our strategy for estimating the relative sea level change at Kapoho comprises referencing
the Kapoho region land-motion to Hilo via the InSAR map and then using the long-term
tide gauge record of water level changes at Hilo to yield a RSL rate at Kapoho. In so doing,
we make the assumption that between Hilo and Kapoho the water level changes are
constant. This assumption is verified by Caccamise et al. (2005) who show that although
Hawai`i is a place of strong steric sea-level trends (due to ocean thermal expansion), the
contribution to water level changes between Kapoho and Hilo woul
cm/yr.
12
13
Caccamise et al. (2005) reported -0.21±0.06 cm/yr vertical motion of the continuous GPS
station, ÓHILOÔ (Figure A.5) with respect to a reference frame in which stations around the
Pacific margin are held fixed. However, over baselines as long as those used in the
Caccamise et al. (2005) study, it is unlikely that absolute vertical velocities are know to better
than ~ 2 mm/yr and so for the purposes of this report we take th
0.21±0.2 cm/yr.
To convert the Hilo tide gauge sea-level trend (tg= 0.31 cm/yr) to the RSL trend at
HILO
Kapoho (rsl), we first compute the VLM trend at the Hilo CGPS site (vlm).
KAPOHOHILO
Caccamise et al. (2005) cited historic leveling data to show that there is negligible motion
between the CGPS site and the National Ocean Services (NOS) tide gauge (500m
separation), so L is an accurate proxy for VLM at the Hilo tide gauge. We use the
HILO
convention that a negative VLM rate corresponds to a net downwar
time. rsl = tg + vlm = 0.31 cm/yr Ï 0.21 ° 0.2 cm/yr. = 0.1 ± 0.2 cm/yr. Then the
HILOHILOHILO
InSAR vertical displacement rate at Kapoho is subtracted from rsl, which gives the RSL
HILO
trend at Kapoho, rsl = rsl - vlm. In Table 2 we give the estimates for the
KAPOHOHILOKAPOHO
range of VLM values at Kapoho.
0.1 -0.7 0.8
0.1 -1.6 1.7
Estimation of relative sea level (rsl) rates at Kapoho for maximum and minimum vertical land motion values (vlm)
= rsl - vlm.
observed with InSAR. As noted in the text, rsl
KAPOHOHILOKAPOHO
Conclusion & Recommendation
We analyzed InSAR data from the Envisat platform to estimate a
motion values of Kapoho with respect to Hilo of between ~ -0.7 a
cm/yr (2 standard deviations) for the time period of February 2003 to march 2006. Using
these values and the long-term Hilo tide gauge record, we estimate that relative sea level
changes at Kapoho are ~ 0.8 to 1.7 cm/yr ± 0.8 cm/yr (2 standard
important conclusion is that VLM values at Kapoho are likely at least an order of magnitude
greater than the sea-level change recorded at the Hilo tide gauge and so local land motion
dominates the relative sea-level change rate over these short ti
Our analysis says nothing about the cause of subsidence at Kapoho or whether the observed
VLM will continue in the future, though we note that it has now
since the Kalapana earthquake and we would expect it be unlikely that the region is still
experiencing such large postseismic effects (i.e. Scholz, 1990).
We recommend continued monitoring using a combination of InSAR, continuous GPS, and
tide gauge techniques in the region. More InSAR acquisitions wil
errors; installation of a single continuous GPS station on the coast at Kapoho would allow
14
15
for high resolution time series monitoring of VLM; the tide gauge data would allow direct
measurement of sea-level change at Kapoho and then allow any mea
reference strictly locally.
Appendix: GPS High Tide Surveys
We carried out ground-based surveys of the high tide position
times: August 17, 2005 and July 10, 2006. The surveys comprised laying out a string marking
the high tide point and walking the string backpacks and dual f
equipment (Trimble NetRS receivers with Zephyr antennae). On the first survey both Drs.
Brooks and Foster of the PGF carried dual frequency equipment. On the second survey Dr.
Foster carried dual frequency equipment and Shanna-Lei Dacanay c
The data were processed in the PGF labs using PAGES software fro
Geodetic Survey.
The locations of the high tide positions are shown in Figure A.6
oceanographic factors which could contribute to the different lo
between the two survey dates and so we ascribe no significance to the different positions
shown in the plots.
From the first yearÔs survey results, we find a best-fitting plane to the data in a least-squares
-4
sense and then calculate the regional slope as 3.5x10degrees.
16
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