Loading...
HomeMy WebLinkAboutMulti-Hazard Mitigation Plan: 05. Tropical Cyclones CIVIL DEFENSE AGENCY COUNTY OF HAWAII 920 ULULANI STREET HILO,HAWAII 96720 r f 5. Tropical Cyclones Chapter 5:Hazard Analysis—Tropical Cyclones CHAPTER 5 - TROPICAL CYCLONES 5.1 Description of Hazard Tropical cyclones are storms that originate over a warm tropical ocean. When such a storm develops sustained winds (one minute average) over 74 miles per hour, it is classified as a hurricane.15 They are characterized by a large counterclockwise circulation of air and lower barometric pressure near the center. These actions produce the major hazards of hurricanes: high winds, high waves, storm surge, and heavy rain. These hazards cause flooding, salinization of water supplies, agricultural crop losses, erosion, loss of life, and damage to structures and infrastructure. The winds can affect all parts of an island and can be intensified by mountain ranges (orographic or topographic amplification). A good example was Hurricane Iwa in 1982; it was barely a Category 1 hurricane but winds in the Wahiawa area of Oahu equaled those in areas on Kaua'i, which was closest to the path of the storm. Meteorologists consider the notion that Mauna Loa and Mauna Kea "protect" Hawai'i Island from hurricanes to be unfounded. Waves and storm surges normally hit coasts ahead of high winds, as waves move faster than a hurricane advances. Locally intense rainfall may occur as the hurricane makes landfall.16 Thus hurricanes,though rare in Hawai'i, are complex hazards. 5.1.1 Coastal Wave/Surge Storm surge is the rise of water above sea level at the time of storm onset. The height of storm surge along the open coast depends on a number of factors, which include: (1) wind speed and associated barometric pressure, (2) depth of water or shoaling factor, (3) storm trajectory, and (4) speed of the storm. Coastal configuration in the form of estuaries or bays can cause a funneling or amplification effect. Coincidence with high tide will also increase surge height. Although the maximum surge usually affects only a relatively short length of coastline, combined storm surge and wave action may have damaging effects over the entire coastline facing a major storm center. Wind-driven waves on top of the storm surge pose a number of added problems. In Hawaii the wave run-up typically floods areas not reached by the surge itself. The scouring power of waves is considerable. The storm surge is the most dangerous part of a hurricane as pounding waves create very hazardous flood currents. About 90% of the deaths experienced in the past near the coast resulting from hurricanes are caused not by wind,but by storm surge. Stream flooding is also much worse inland during the storm surge because of backwater effects. 15 In the western Pacific,hurricanes are called"typhoons"; similar storms in the Indian Ocean are called"cy- clones". An organized system of clouds and thunderstorms with a defined circulation and maximum sus- tained winds of 38 mph or less is called a "tropical depression". An organized system of strong thunderstorms with a defined circulation and maximum sustained winds of 39 to 73 mph is called a"tropical storm". 16 Schroeder, Tom, 1993,"Hawaii Hurricanes: Their History, Causes, and Future," Office of State Planning, December 1993. 5-1 Hawaii County Multi-Hazard Mitigation Plan Chapter 5:Hazard Analysis—Tropical Cyclones The duration of storm surge is usually relatively short,being dependent upon the elevation of the tide, which rises and falls twice daily in most coastal places and the speed of a storm's onset. In Hawaii, the high velocities of hurricane winds often produce wave heights higher than the maximum level of the prevailing high tide or of the surge itself. In studying the aftermath of Hurricane Iniki it was discovered by researchers at the Army Corps of Engineers and the University of Hawaii (Fletcher and others, 1994)that the greatest threat related to hurricane overwash in the Hawaiian Islands is due to water-level rise from wave forces rather than wind forces. This differs from the mainland where the wind in a hurricane is known to drive water against the coast and cause flooding, called wind set-up. During Iniki, the strongest component of the overwash was the result of large waves, called wave set-up. Wind set-up appeared to be relatively less important. Other factors leading to coastal overwash are the low atmospheric pressure, the tide stage, coastal topography, and the location relative to the eye of the hurricane. Overwash mitigation must be enacted prior to the event. This would include adequate building setbacks so that development does not occur in high hazard areas of the coastal zone, elevation of existing structures to recommended levels, break-way ground floor walls that permit overwash flooding without compromising an entire structure, and other coastal construction techniques designed to reduce flood damage. FEMA has incorporated hurricane inundation from model scenarios into a flood insurance study for all islands including Hawaii, as discussed in the section below. 5.1.1.1 Hurricane Flood Insurance Study for the Hawaiian Islands The Hurricane Flood Insurance Study for the Hawaiian Islands was conducted under FEMA contract number EMW-2003-CO-0046, RMTC/URS Task Order 013. Under this contract, RMTC/URS, a joint venture consisting of R.M. Towill, URS, Dewberry, TerraPoint, Airborne 1, and Sea Engineering, was tasked to evaluate and map the magnitude and extent of coastal hazards due to hurricanes for six Hawaiian Islands, divided into four counties: Kauai (Kauai County), Oahu (City and County of Honolulu), Molokai, Maui, Lanai (Maui County), and Hawaii (Hawaii County). Although the effective (i.e., past) FIRMs for each county have accounted for tsunami hazards, the hurricane flood hazard had not been previously separately evaluated in a comprehensive study throughout the islands. In general, the hurricane coastal hazard analysis was limited to the southern coast of each island. This is due to several factors, including the predominance of tsunami hazards and limited low-lying areas susceptible to hurricane hazards along the north shore of the islands. Table 5-1 provides a summary of study limits. 5-2 Hawaii County Multi-Hazard Mitigation Plan Chapter 5:Hazard Analysis—Tropical Cyclones Table 5-1. Summar•of Study Limits Island Western Limit Eastern Limit Reach Length (Miles) Hawaii Upotu Point Cape Kumukahi 193 Kauai Nohili Point Kuaehu Point 56 Lanai Katunalapau Manele 16 Maui Honokahua Bay Koali 69 Molokai Clio Point Cape Halaawa 54 Oahu Kaena Point Kawaihoa Point 60 Total: 448 Ksua� Dahu Molokai LanaiMaui Hawaii Figure 5-1. Extents of Hurricane storm surge inundation study Transects were laid-out within the study limits and representative placement was evaluated during the field reconnaissance performed from July 24th through August 6`h, 2007. The topographic base consisted of LiDAR collected under FEMA Task Orders 12 and 26. The LiDAR data were collected in the Fall of 2006, post-processed to bare earth and quality controlled to meet FEMA mapping standards. These data were assimilated together with the best available bathymetric datasets, including USACE hydrographic LiDAR, into high- resolution seamless digital elevation models. The hazard analysis considered the combination of storm surge and hurricane-induced wave hazards. This included independent analysis and/or modeling of storm surge, return frequency flood elevations, wave setup, overland wave hazards, and wave runup. The ADvanced CIRCulation model for coastal ocean hydrodynamics (ADCIRC) was selected to develop the stillwater elevations or storm surge for the study area. The Empirical Simulation 5-3 Hawaii County Multi-Hazard Mitigation Plan Chapter 5:Hazard Analysis—Tropical Cyclones Technique (EST), also developed by the USACE, was used to determine the stillwater frequency curves for the 10-, 2-, 1-, and 0.2-percent annual chance stillwater elevations. Deepwater wave conditions were determined using the Shore Protection Manual (SPM) prediction technique and limited fetch analyses were performed in harbor and sheltered areas. Wave setup was differentiated and evaluated for areas with and without fronting reefs. Areas of primary frontal dune were identified, delineated, and eroded. Overland wave propagation hazards were evaluated using the WHAFIS model. Wave obstructions were verified at representative transect locations by field reconnaissance. Wave run-up was evaluated using the RUNUP 2.0 and TAW methodologies, depending of the presence of reefs and local steepness of the bathymetry. Wave hazard analyses were conducted at FTS transect locations, in addition to more tightly- spaced"mapping transects." These additional transects were facilitated by the application of an integrated GIS toolset that automates repetitive modeling tasks, and enables a more detailed analysis than typical coastal FIS studies. Wave setup values were assigned to these transects according to analysis at adjacent FIS transects. Otherwise, the mapping transects were treated with the same overland wave propagation and wave runup assessments as the FTS transects. The coastal hazards determined from the above analyses were synthesized in the form of the standard FEMA special flood hazard boundaries for the Zone VE, Zone AE, Zone AO, and Zone X hazard areas. These are presented in the TSDN as workmaps produced at a scale of 1':500". The workmaps also include stillwater stations, topographic elevation contours, FIS and mapping transect locations, and the shoreline. Wave analysis for the 0.2% annual chance event was not included in the scope of the study. The 0.2% return frequency stillwater elevation was exceeded by cumulative flood elevation from the 1% stillwater elevation and wave setup, therefore, the boundary of the 0.2% annual chance event was not delineated. In steeper areas where mapping scale limits the gutter placement, the SFHAs are only identified by the position of the 100-yr flood boundary. Mapped Base Flood Elevations (BFEs) are considerably dependent to the topographic representation at each transect. As a result, localized variations in the topography at other locations may not be fully reflected in the mapped SFHAs and BFEs. A Technical Support Data Notebook (TSDN) was compiled for each county in the study area. Storm surge and return frequency elevation analyses were inclusive of all counties, and thus all materials pertaining to those analyses, including model input, output, and documentation are included in each county TSDN. The remainder of the data, including wave modeling, mapping, workmaps, topography, etc., are island and county specific. Therefore,these data are only presented in the appropriate countywide TSDN. Limitations of the study and need for evaluation prior to FIRM adoption: • There will need to be post-DFIRM modifications to the Flood Maps if tsunami inundation is to be any factor in zoning and construction requirements. 5-4 Hawaii County Multi-Hazard Mitigation Plan Chapter 5:Hazard Analysis—Tropical Cyclones • Phase I: The first step is to compare the differences between the existing and new FIRM maps to determine where historic or the recently modeled tsunami hazard is greater. • Phase II: UHM SOEST mapping (by Kwok Fai Cheung) can produce 100-year and 500-year probabilisitic tsunami hazard maps to provide future local modifications to the DFIRMs. 5.1.2 High Winds The hazard from hurricane winds is far more extensive than the water hazard. Both ex- periencc and analyses indicate that certain locations will experience stronger winds. Hurricane winds, blowing from variable directions, will experience analogous variations. This orographic (or topographic) amplification is the reason a minimal hurricane such as Iwa can have significant wind effects. The NWS hurricane reports assume landfall at a flat Atlantic or Gulf coast state, and no amplification. Since wind forces increase proportionally to the wind speed squared, any amplification of the basic wind speed may significantly increase its effects. 5-5 Hawaii County Multi-Hazard Mitigation Plan Chapter 5:Hazard Analysis—Tropical Cyclones Table 5-2. Satlir Simpson Scale and damage potential Central Pressure Hurricane Sustained Fastest Peak Gust Approximate Mm of Sea level Mile Speed (over land) Storm Surge Damage Potential(with tropical Pacific amendments) Category mercury at 0 y�rtrd' mph mph Height(ft.) degrees C(32 Pressure degrees F) (inches) Tropical <40 mph <2 ft Virtually None. Some small dead limbs,ripe coconuts,and dead Depression (<64 1rrnMr) 0.61 m) <1008 <29.77 palm fi-ca ds m blown fia trees. Some(agile and tender green leaves (< blown firm trees such as papaya and Meshy broad leaf plants. 40-73 mph Some.Minor damage to buildings of light material. Moderate Tropical 2-3 ft damage to banana trees,papaya trees,and most fleshy crops. Large Storm 979-1007 28.91-29.74 (64- (0.61-0.91ni) dead limbs,ripe coconuts,many dead palm fronds,some green 117km/hr) leaves,and small branches blown fiam trees. Significant.Corrugated metal and plywood stripped from poorly constructed or termite-infested structures and may become airborne. Some damage to wood roofs.Major damage to banana trees,papaya 74-95 mph trees,and Ileshy crops. Some palm fronds tarn Hour the crowns of 1 980-992 28.94-29.30 (118-153 67-88 82-108 4-5 ft most types of paten trees,many ripe coconuts blown from coconut kmMr) (1.22-1.52m) palms. Some damage to poorly constructed signs.Wooden power poles tilt,some rotten power poles break,termite-weakened poles begin to snap. Low-lying coastal roads inundated,minor pier darnage,some small craft in exposed anchorage torn from moorings. Moderate. Considerable damage to structures made of light materials.Moderate damage to houses.Exposed banana trees and papaya trees totally destroyed,10%.-20%defoliation of trees and 96-110 mph shrubbcry. Many palm fronds crimped and bent through the clown 6-8 ft 2 965-979 28.50-28.91 (178-209 SS-I 10 108-13U f ococonut palms and several green fronds tipped hour palm trees; kin/hr) (1.83-2.44 in) some trees blown down.Weakened power poles snap.Considerable damage to piers;marinas flooded.Small craft in unprotected anchorages torn from moorings.Evacuation from some shoreline residences and low-lying areas required. Extensive.Extensive damage to houses mid small buildings;weakly constructed and termite-weakened house heavily datuaged or destroyed;buildings made of light materials destroyed;extensive damage to wooden structures.Major damage to shrubbery and trees; 111-131 9-12 ft up to 50%of palm fonds bent m blown off;numerous ripe and many 3 945-964 27'91 nnph 110-136 130-156 (274-3.66 green coconuts blown off coconut palms;crowns blown off of palm 28.47 (178-209 trees;up to 10%of coconut palms blown down;30%-5O% km/hr) m) defoliation of many trees and shrubs.Large trees blown dowm.Many wooden power poles broken or blown down;many secondary power lines downed.Air is frill of light projectiles and debris;poorly constructed signs blown down.Serious coastal flooding;larger structures near coast damaged by battering waves and floating debris. Extreme. Extreme structural damage;even well-built structures heavily damaged or destroyed;extensive damage to non-concrete failure of many roof structures,window frames and doors,especially unprotected,non-reinforced ones;well-built wooden and metal structures severely daniaged or destroyed.Shrubs and trees defoliated;up to 75%of palm fronds bent,twisted,or bloom off. 131-155 13-18 ft Many crowns stripped from paten trees;nunerous green and virtually 27.17- mph all ripe coconuts blo�nm from trees;severe damage to sugar cane; 4 920-944 P 136-16y 156-191 1296-5.4y 1 b 27.88 (210-249 large Gees blown down;bark stripped from trees;most standing trees km/hr) ui) are void of all but the largest branches(severely pruned),with remaining branches stubby in appearance;hunks and branches are sandblasted.Most wood poles downed/snapped;secondary and primary power lines downed.Air is full of large projectiles and debris.All signs blown down.Major damage to lower floors of stmctm-e,due to flooding and battering by waves and floating debris. Major erosion of beaches. Catastrophic. Building failures;extensive or total destruction to >155 mph norrcoricTete residences mid industrial buildings;devtxting damage >IS ft to roofs of buildings;total failure of non-concrete reinforced roofs. 5 <920 <27.17 (>250 (>5.49 on Severe damage to virtually all wooden poles;all secondary power km/hi) lines and most primary power lines downed.Small buildings overturned or blown away. 5.2 Significant Historical Events Little was recorded of hurricanes striking Hawaii before the last half of the 20th century. Since 1950, when adequate records began, eight hurricanes have affected the Hawaiian 5-6 Hawaii County Multi-Hazard Mitigation Plan Chapter 5:Hazard Analysis—Tropical Cyclones Islands and 12 others have posed a threat by their passage.17 The only documented hurricane before 1950 was the "Kohala Cyclone" of 1871 which was believed to be a minimal hurricane that affected Maui and Hawaii. The path of hurricanes can be quite variable and unpredictable as illustrated by Hurricane Iwa (see Figure 5-2). Table 5-3 below lists the significant hurricanes affecting the state of Hawaii since 1950 and Figure 5-3 shows the tracks of these hurricanes and tropical storms. Table 5-3. Significant Hurricanes Since 195018 Name Year Estimated Loss $ Effects Hiki 1950 200,000 flooding on Kauai Della 1957 high surf,Kaua i Nina 1957 100,000 high waves,Kauai Dot 1959 6,000,000 $150,000 on Oahu and Hawaii Fico 1978 180,000 East Hawaii Susan 1978 — Iwa 1982 312,000,000 Kauai and Oahu Iniki 1992 1,800,000,000 all islands 17 Haraguchi,Paul, 1984,"Hurricanes in Hawaii",report for U.S.Army Corps of Engineers,March 1984. 18 Hurricanes Dot,Iwa,and Tniki were the only storms that exhibited hurricane-force winds in the Hawaiian Islands;the others were rated as hurricanes by measurement from aircraft,away from land stations.Wave action from these storms may still affect the islands. 5-7 Hawaii County Multi-Hazard Mitigation Plan Chapter 5:Hazard Analysis—Tropical Cyclones 25 06:00 Sep 12 959 mb Buoy 1 p 06:00 Nov 24 23:51 Nov 23 Kauai 969 mb 00:00+Oahu Sep 12 '"' Maui 18:29 Nov 23 945 mb e� 20 968 mb Hawaii Buoy 3 18:00 Sep 11 A 938 mb Z 12:00 Sep 11 N 940 mb Buoy 4 OBuoy 2 06:00 Sep 11 J 23:30 Nov 22 947 mb 964 mb 00:00 Sep 11 ` 948 mb 15 I 12:00 Sep 10 I 960 mb / 00:00 Sep 10 12:00 Sep 9 980 mb 992 mb / UTC 00:00 Sep 9,1992 / Iniki 996 mb UTC 00:00 Nov 20,1982 1000 mb Iwa 10170 165 160 155 150 Longitude(W) Figure 5-2. Track of Hurricane Iwa and Iniki(Cheung,K.F.2003) 1 1 1 Tracks of Central Pacific Hurricames from 1949 to 1998 I z Calegary 1 1 r Category 3 + Tr_^rw rds aldt F �hh e�lk AUGUST MEAN COOLER wh +4 7 UGEAN WATER<e*F 4AP4 4� � 4L1f4US1:KIEA�+ AUGUST MEAN WARMER DCEAN WATER>STF -46K i y;r i 7,f 1d0' 1'JG' 110' Figure 5-3. Historic Central Pacific hurricane tracks 5-8 Hawaii County Multi-Hazard Mitigation Plan Chapter 5:Hazard Analysis—Tropical Cyclones 2Q Contra] Pacific Hurricane Occurrence n , All hurricanes Hurricanes?category 3 4 Month Figure 5-4. Central Pacific Hurricane Occurrences by month 5.3 Probability of Occurrence The Saffir-Simpson Scale classifies the potential severity of hurricanes. However, this scale may not fully address the risk for mountainous Pacific islands such as Hawaii. The Saffir- Simpson Scale was developed for flat coastal areas with a continental shelf where the winds over the land diminish relatively quickly accompanied by heavy rain. In Hawaii,the variable topography accelerates the winds in certain areas such that one area may be receiving wind speeds at a tropical storm level,while another area may be receiving hurricane-force winds. The number of tropical cyclones in the Central Pacific varies from none to ten annually, and few develop beyond the intensity of a tropical storm. The Hawaii Hurricane Relief Fund (HHRF), originally established after Iniki induced insurance companies to drop coverage in Hawaii, produced several studies on the probability of this hazard (including Applied Research Associates, 2001).19 (Other studies by Peterka & Chock have been concerned with estimating hurricane effects through Monte Carlo simulation models and analysis of topographic effects.) 5.3.1 Probabilistic Hazard Analysis and Scenario Simulations Studies sponsored by the NASA Office of Earth Science and the HHRF have developed new models for estimating the long-term probabilities of Pacific hurricanes. As of 2002, a much improved methodology was used by Peterka in Windspeed Mapping of Hawaii and Pacific 19 Applied Research Associates(ARA),2001,"Hazard Mitigation Study for the Hawaii Hurricane Relief Fund"(incorporates part of FEMA-sponsored Iniki Building Performance Report),December 2001. 5-9 Hawaii County Multi-Hazard Mitigation Plan Chapter•5:Hazard Analysis—Tropical Cyclones Insular States by Monte Carlo Simulation, to establish design hurricane windspeeds for individual islands reflecting their differential hazard. While Hawaii Island has not had a direct hit by a hurricane, the Peterka model sponsored by NASA indicates that Hawaii Island has a long-term hurricane hazard higher than the other islands (see Figure 5-5 and Table 5-4). However, the ASCE 7-2010 Standard accepts the ARA model which has approximately uniform wind hazard across all islands of the State (Figure 5-6 and Figure 5-7). Topographic effects are reflected in the Hawaii State Building Code. The effective wind speed map of Figure 5-8 shows this effect of speed-up relative to a code design reference windspeed of 105 mph. 30 10 20 -170 -160 -150 -140 -130 -120 -110 -100 Figure 5-5. Eastern and Central Pacific Hurricane frequency map.Contours show number of times a hurricane (intensity>64 knots)passes within 75 Nmi per 10 years. (Peterka,2002) Table 5-4. Hurricane Winds peed vs.Recurrence Interval and Modern-Da•ASCE Design Speed, Peak Gust 10 m Peterka Peterka HHRF study Peterka Open Country Uhue Oahu Hawaii Average Hilo Exposure in mph 50-year 75 80 66 96 100-year 90 95 87 114 500-year 128 134 122 150 5.3.2 ASCE 7-10 The ASCE 7-10 standard will formally designate Hawaii as a Special Wind Region where the authorities having jurisdiction (State and Counties) shall establish the effects of topography on the basic wind speed. C6.5.4.1 Special Wind Regions. Although the wind speed map of Fig. 6-1 in ASCE 7 is valid for most regions of the country, there are special regions in which wind speed anomalies are known to exist. Winds blowing over mountain ranges or through gorges or 5-10 Hawaii County Multi-Hazard Mitigation Plan Chapter•5:Hazard Analysis—Tropical Cyclones river valleys in these special regions can develop speeds that are substantially higher than the values indicated on the default map. The Hawaii State Building Code provides maps showing the net effect of such topography. 185 180 175 174 170 165 10 1 160 15.5 150 145 X43 140 135 130 Peak Gust 120 Windspeed 115 13 (mph) 110 10.5 100 ss 50 1 P51/ i 85 80 75 70 65 67 60 55 50 45 40 Governed Governed by Hurricanes 3o by slorms zs 20 15 10 5 0 10 100 1000 10000 Years Figure 5-6. Wind speed recurrence intervals for Hawaii(from ASCE 7-2010 Standard) '1'.4RLR C6-2 APPROXIMATE.RELATIONSHIP BETWEEN WIND SPEEDS IN ASCE 7 10 AND SAFFIR/SIMPSON HURRICANE SCALE Sat'15r/Simpson Sustained Wind Gust Wind Speed Over Gust Wind Speed Hurricane Speed Over Water" Water" Over Land` Category Mph (eu/s) mph (m/s) mph (eu/s) 1 74-95 33-43 87-111 39-50 81-105 36-47 2 96-110 44-49 112-129 51-58 106-121 48-54 3 111-134) 54-58 130-152 59-68 122-143 55-64 4 131-155 59-69 153-181 69-81 144-171 65-76 5 >155 >69 >181 >81.0 >171 >76 "I-minure average wind speed at 33 ft(0 m)above open water -.second rst wind.speed at 33 ft(10 m)above open water `3-second gust wind speed at 33 R f 1 m)above open ground in Exposwc Category C.This column has the same basis(avcragmg nme„heigh4 and exposure)as the basic wind spcud fiom Fig.6-1. Figure 5-7. ASCE 7-10 relationship between Saflir/Simpson category and wind speed 5-11 Hawaii County Multi-Hazard Mitigation Plan Chapter 5:Hazard Analysis—Tropical Cyclones Effective Wind Speed for the Island of Hawaii (For Components and Cladding with Mean Roof Height not geater than 100ft) District Boundary Land use CONTOUR Major Road 0 Agriculture ------ g0 Conservation 100 Rural ---------- 110 ••. .' �� ............' Urban —120 —_ -- -130 140 _ — ---150 —160 - _ �J _�• j r:.- --170 180 `-.1-: I r U I I / 1�1 l i i ...... I .1 N f � / 0 5 10 20 Mik+,. I I Figure 5-8. Effective wind speed map(mph)for Hawaii Island(Chock,2007) 5.4 Risk Assessment Average Annualized Loss (AAL) is an objective measure of future losses averaged on an annual basis. This information can be very useful in assessing the relative contributors to total natural hazard losses. Formula Expression: AAL=Y Li x Pi Li—Estimated Loss for Event i Pi—Annual Probability of Event i 5-12 Hawaii County Multi-Hazard Mitigation Plan Chapter•5:Hazard Analysis—Tropical Cyclones Description: Sum of the expected loss for each event (i.e., sum of the products of the estimated loss from each event and that event's rate of occurrence) A tool used to calculate AAL due to tropical cyclones is the HAZUS MH model. The wind speed recurrence intervals used by the HAZUS model are calculated based on the probability of tropical cyclone impacts, and high winds resulting from other effects (Kona Storms, high trade winds, etc.) are not specifically accounted for. Although the recurrence interval of these non-cyclonic wind storms is high, perhaps several storms per year, the magnitude of the winds and associated losses are generally small therefore it can be generally assumed that these storms will not contribute significantly to the AAL calculated for tropical cyclones. Based on a HAZUS AAL analysis incorporating Hawaii Construction Cost Data, tropical cyclone AAL is about $69 million in Hawaii County. The predominant contributor to loss is single-family residential construction. County Hawaii County Tropical Cyclone AAL $69 million per year The HAZUS model can also be used to determine probabilities of varying degrees of damage to site specific facilities. To determine AAL, HAZUS computes losses, Li, for seven earthquake scenario events with different return periods (1/exceedance probability): 10-year, 20-year, 50-year, 100-year, 200-year, 500-year, and 1000-year. The Probability versus Loss Curve is approximated through curve fitting, and the area under the fitted curve is integrated to obtain the AAL results. A risk assessment has been conducted for essential facilities in Hawaii County. From this analysis the facilities were ranked based on their expected losses and loss of functionality. 5.5 Mitigation Strategies 5.5.1 Previous/Current Efforts 5.5.1.1 Construction Standards As described in Chapter 4, the design vintage can be used as an indicator of a buildings susceptibility to wind damage. Design wind pressures, typical construction type (single or double wall), and use of hurricane uplift resistance can all be determined by the year built based on the corresponding version of the UBC or IBC in effect at the time. Table 5-5 and Table 5-6 provide statistics of the number of homes built under each version of the UBC and their probable uplift resistance. Most existing homes have no hurricane mitigation 5-13 Hawaii County Multi-Hazard Mitigation Plan Chapter 5:Hazard Analysis—Tropical Cyclones Table 5-5. Wood frame,double wall,residential construction statistics for Hawaii County Hawaii County(Double Wall Construction) Effective Date Year of UBC Hurricane Tie Requirement Number of Residences February 8,1962 1961 None 648 April 17,1968 1967 None 194 August 8,1972 1970 None 1416 41%Without Roof Strap February 25,1975 1973 None 1065 December 11,1978 1976 None 2600 January 19,1985 1982 None 5010 December,1993 1991 UBC Appendix Load Path 12126 59%With Roof Strap July,1999 1994 UBC Appendix Load Path 3759 Total= 26818 Table 5-6. Wood frame,single wall,residential construction statistics for Hawaii County Hawaii County (Single Wall Construction) Effective Date Year of UBC Hurricane Tie Requirement Number of Residences February 8, 1962 1961 None 8723 April 17, 1968 1967 None 2109 August 8, 1972 1970 None 2471 91%Without Roof Strap February 25,1975 1973 None 931 December 11, 1978 1976 None 1088 January 19, 1985 1982 None 1378 December, 1993 1991 UBC Appendix Load Path 1271 9%With Roof Strap July, 1999 1994 UBC Appendix Load Path 293 Total—1 18264 5.5.1.1.1 Windborne Debris Protection Hawaii is considered a windborne debris region per the ASCE 7 standard; this requires additional measures for basic windborne debris protection, and also special cases where even higher strength of enhanced glazing protection (such as health care and large assisted living facilities,public assembly, and essential and emergency response facilities) is further defined in the building code. In previous versions of ASCE 7 it was permitted, if the basic windborne debris protection was not provided, to design the building for the additional internal wind pressure resulting from window breakage. That internal pressure can raise the forces on structural and cladding components by as much as 100%higher (double). The current ASCE 7-05 does not allow for unprotected opening of buildings located within the windborne debris region, it simply states: 5-14 Hawaii County Multi-Hazard Mitigation Plan Chapter•5:Hazard Analysis—Tropical Cyclones Glazing in buildings located in wind-borne debris regions shall be protected with an impact resistant covering or be impact-resistant glazing according to the requirements specified in ASTM E1886 and ASTM E1996 or other approved test methods and performance criteria. The levels of impact resistance shall be a function of Missile Levels and Wind Zones specified in ASTM E1886 and ASTM E1996. EXCEPTIONS: 1. Glazing in Category Il, III, or IV buildings located over 60 ft (18.3 m) above the ground and over 30 ft (92 m) above aggregate surface roofs located within 1,500 ft (458 m) of the building shall be permitted to be unprotected. 2. Glazing in Category I buildings shall be permitted to be unprotected. The Hawaii State Building code allows for the construction of a safe room in residential construction in lieu of the windborne debris protection requirements. This essentially reinstates the previous versions of the ASCE 7 where unprotected glazing is allowed in a windborne debris region although, it must be considered as an opening when determining the enclosure classification. 5.5.1.2 Utilities Damaged or destroyed utility lines and facilities — including electricity, computer and satellite links, gas sewer, and water services — can cripple a region after a disaster. Power lines are often badly damaged or destroyed resulting in the loss of power for days, weeks or even months as in the case of Hurricane Iniki. In addition to basic modern household appliances being affected, public water supplies, water treatment and sewage facilities can also be impacted. Electric pumps cannot pump drinking water into an area without power. Disaster victims who do get water may have to boil it to eliminate waterborne pathogens introduced to the supply in breached areas. Electrical transmission and distribution lines have been particularly susceptible to failure in previous hurricanes, with 30% of the wooden power distribution poles and 26% of transmission poles on Kauai failing during Hurricane Iniki. This has resulted in periodic updates to the design criteria for these poles. The most recent design criteria were adopted by the State Public Utility Commission as Hawaii Administrative Rules 6-13, and are based on the 2002 National Electrical Safety Code which references the ASCE 7 wind load criteria. While this would an improvement to the local design standards it does not incorporate the latest Hawaii specific wind design criteria. It is recommended that the future mitigation project should further update the transmission and distribution line design criteria to incorporate the Hawaii specific wind design criteria and utilize the effective wind speed maps that account for topographical, directionality and local exposure. Procedures should be implemented to assure the adoption of the new standards so that when a power pole fails and is replaced, the replacement should meet the current standards. 5-15 Hawaii County Multi-Hazard Mitigation Plan Chapter 5:Hazard Analysis—Tropical Cyclones 5.5.1.3 Wind Speed-Up and Structure Type Vulnerabilities Structures are designed to withstand specified wind forces in accordance with the prevailing building code. Wind design pressures have changed over the years in the Uniform Building Code (UBC), increasing from 15 psf(1958-79) to 26.5 psf(1982-88) to 30 psf(1991-97).20 Hawaii County did not adopt the 1982 UBC until 1985, thus any structures built prior to 1985 are designed to an inadequate wind pressure. Subsequent to Iniki (1992), Hawaii County required hurricane ties for single-family construction with the adoption of the 1991 UBC in 1993. To identify vulnerable single-family housing stock, the suggested benchmark year would be thus 1993. The local Hawaii County building code is based on the 1991 UBC and does not take into account topographically induced local wind acceleration which could produce significant directional sensitivity at a given site. The wind speed-up effects arc now reflected in the Hawaii State Building Code, which needs to be adopted by the County of Hawaii per Hawaii Revised Statute Chapter 107,Part II. 5.5.1.4 Critical Facilities Study An all-hazard screening of critical facility buildings in the County of Hawaii has been conducted and a HAZUS MH risk assessment model created to evaluate the expected losses for each building. Two facilities that rank high based on these analyses were evaluated in more detail such that recommended mitigation procedures were developed. A Benefit-Cost Analysis of the mitigation project construction funding was performed. This detailed evaluation will provide the information necessary to submit a PDM grant application for feasible retrofit project. 5.5.1.5 State Building Adoption/Requirements for Hurricane Resistance The 2006 International Building Code will soon be adopted by all Counties in the State of Hawaii through the recently developed State Building code, which each county must adopt by new state legislation after a grace period that is intended to allow development of any specific requirements a particular county may desire. The state building code is intended to ensure regular updates of the building codes and uniformity between the counties. One significant aspect of the adoption of the upcoming adoption of 2006 IBC statewide is the consideration of windborne debris protection for any glazing lower than 60 feet above the ground level in buildings located in a windborne debris region. Hawaii is considered a windborne debris region and consequently the IBC requires impact protection of the glazing. In lieu of glazing protection, the 2003 iBC allows any unprotected glazing in to be considered as openings and consequently the building must be designed for internal pressurization. This provision is omitted from the 2006 IBC for buildings in wind debris 20 "The 1982 to 1997 UBC values were predicated on an 80 mph basic fastest-mile windspeed, approximately equivalent to a 95 mph 3-second peak gust. The 3-second peak gust is the wind parameter now used in American Society of Civil Engineers 7 (ASCE-7),Minimum Design Loads for Buildings and Other Struc- tures, which forms the basis for the International Building Code (IBC). The 3-second gust windspeed standard now established in the IBC is 105 mph statewide, which is slightly greater than the UBC- equivalent 95 mph 3-second gust. Hurricane Hazard Advisory from the Hawaii Multihazard Science Advisory Committee to the State Hazard Mitigation Forum,draft December 2002. 5-16 Hawaii County Multi-Hazard Mitigation Plan Chapter•5:Hazard Analysis—Tropical Cyclones regions. However, risk analyses found that the benefits of providing windborne debris protection for all glazing did not exceed the costs for the relatively low hurricane hazard in Hawaii. Therefore, the state building code amendments to the 2006 IBC provide designers with flexibility in allowing Occupancy Category II buildings and some Occupancy Category ITT buildings (not healthcare or high occupancy facilities) to be designed with unprotected glazing provided they are designed for the internal pressurization. If a residential building is not provided with glazing protection then it must have a residential safe room installed which does have appropriate glazing protection and must satisfy other structural and non-structural criteria. Public hurricane shelters must also satisfy these criteria. Where used, debris protection for glazing may be in the form of a transparent protective film, on the exterior surface or between glazing layers in laminated glass. Alternatively, window shutters, precut removable plywood panels or another system may be used. Any protective film or other system must undergo testing based on ASTM E 1996 to verify the required level of protection. The University of Hawaii has recently started operation of a wind cannon capable of testing strengthened windows and other debris protective devices to the ASTM standard. This is intending to increase the local availability of products and ultimately reduce the cost of providing windbome debris protection to the glazed areas of a structure. Plywood Shutter Tests Because the HHRF plywood shutter design had not been tested against any of the three windborne debris standards discussed in Section 6.1.1, Applied Research Associates contracted with Dr. Timothy Reinhold of the Wind Load Test Facility at Clemson University to perform exploratory missile impact and pressure resistance tests on six HHRF storm panels. Although it was not feasible to conduct the cyclic loading tests specified in the ASTM standard, the tests did provide valuable information in the impact resistance and ultimate pressure resistance of the HHRF panels. The largest missile specified by ASTM, SBCCI, and the SFBC standards is a 9-pound 2x4 piece of lumber. The missile is projected at the test object using an air canon and strikes the test object end on, perpendicular to the surface. For residential buildings, the missile impact speed specified for regions with the highest design wind speeds in the US is 50 feet per second (34 mph) in all three standards. In order for a product to pass the test, the SFBC impact standard allows no penetration of the protective system while the SBCCI and ASTM standards do allow penetration, provided the hole is small enough to prevent a 3 inch sphere from passing through the hole. The SBCCI and ASTM standards include smaller (lighter) missiles in regions with lower design wind speeds. For gust speeds between 110 and 130 mph, the ASTM standard requires that shutters resist a 4.5-pound 2x4 at 40 feet per second (27 mph). Since Hawaii has a basic design wind speed of 105 mph (gust) in ASCE 7-98, the design speed falls just below the light missile standard. Consequently, impact protection systems for Hawaii would need at most according to current standards)to resist the impact of a 4.5-pound 2x4 traveling at 40 feet pet- second (27 mph). This impact momentum corresponds to that of a 9-pound 2x4 traveling at 20 feet per second(12 mph). All tests were conducted using a 9-pound 2x4. In addition to the straight-on missile impact tests, tests were also conducted with missiles impacting at an oblique angle of 45 degrees. 5-17 Hawaii County Multi-Hazard Mitigation Plan Chapter•5:Hazard Analysis—Tropical Cyclones The test standards also include testing of the panel system for 9000 cycles of pressure fluctuations, of various magnitudes up to the design pressure, after the panel has been subjected to the missile impacts. The tests performed at Clemson University primarily focused on the missile impact portion of the test procedure. Additional tests were conducted where the panels were subjected to uniform wind pressures using air bags or a vacuum chamber. The bulk of these tests were performed to determine the pressure at which the panel would break or be sucked off the wall system. In these tests, the pressures were monotonically increased until failure occurred in the fastening system or to one of the bracing members. Two additional tests were performed using the 6-foot by 6-foot 8-inch sliding glass door protection system to determine the deflection as pressure was increased that pushed the panel against the opening. Two panels were tested for each thickness of plywood and for three sizes of openings (2-foot by 4-foot, 3-foot by 5-foot, and 6-foot by 6-foot 8-inches). Generally, the missile impacts caused localized punching shear failures and it was possible to impact a single panel with multiple missiles. The overall observation is that the shutter systems are adequate to provide protection from the 8-pound 2x4 missile traveling at 27 mph since the threshold for penetration is slightly higher than 24 mph with the 9-pound 2x4 missile. At 24 mph, localized damage to the cross members and indentation of the panel was the rule. There were a couple of instances where a 9-pound missile penetrated at 24 mph, however these were relatively rare. There was a marginal increase in resistance for the 5/8-inch thick sheathing as opposed to the 1/2-inch sheathing. The increase was generally on the order of 1 to 2 mph in missile speed for penetration. The 5/8-inch sheathing did seem to perform better than the 1/2-inch sheathing when subjected to the missile impacts at 45 degrees. The missile bounced off the 5/8-inch sheathing more often than for the 1/2-inch sheathing. In general, 9-pound missiles penetrated the panels at speeds between 25 and 28 mph. The performance of the panels subjected to oblique angle impacts seemed to depend to some extent on whether the missile impacted with the long edge (3-1/2 inch)oriented vertically or horizontally. Local damage to the lx') lumber used at the laps between the plywood sheets was common if impact occurred on the 1x3 and fasteners withdrew or the 1x3 split when the impact occurred near the W. The screws connecting the lx3s to the panels were fairly short and provided only minimal penetration into the plywood sheathing. In summary, the 1/2-inch and 5/8-inch shutters both clearly provide substantial protection from missile impacts associated with a 4.5-pound 2x4 missile and essentially are very close to completely rejecting impacts of an 8-pound 2x4 traveling at 40 feet per second (27 mph). Based on these test results, we conclude that the HHRF protective panels should be an adequate level of protection against windborne debris provided that they are properly constructed and installed. Pressure cycling tests should be conducted to ensure that the anchor design meets the full ASTM standard. Each test specimen is required to receive two such impacts followed by cyclic pressure loading similar to that experience under hurricane conditions. The glazing was required to resist the pressure loading with no crack forming longer than five inches through which air could pass or with no opening forming which a three-inch diameter sphere could pass. 5-18 Hawaii County Multi-Hazard Mitigation Plan Chapter 5:Hazard Analysis—Tropical Cyclones 5.5.2 Future Plans Recommended future hurricane hazard mitigation projects are listed below: Project Description Status Adopt IBC 2006 per HRS 107 Part II; High Windspeed areas are now Not effective for new Identify high windspeed areas and mapped,and have been adopted in construction until county vulnerable structures the State Building Code(2009 adopts IBC 2006;can be used to evaluate risk to existing buildings Adapt HAZUS-MH or other hazard Incorporate Hawaii building Proposed Planning Project; modeling to Hawaii Island inventory and critical facilities into The HAZUS model now has the HAZUS MH wind risk model. a realistic building inventory Hurricanes will cause much higher for Hawaii and Maui,but it losses than earthquakes to residential needs to be converted to the buildings;vulnerable structures can building modeling scheme be identified with respect to high used for hurricane analysis. wind zones Emergency shelter evaluation;Harden Perform a 1-year study to identify Proposed Project; public schools for emergency shelters. and rank Hawaii building types that Then follow-up with the more There is a shortage of shelter buildings in could be deemed safer for hurricane detailed DAGS-standardized Hawaii County. Of the 14 hurricane resistance without exhaustive site structural evaluation shelters on the island,only four shelters investigations. Use this screening procedure for those public have been evaluated for safety by DAGS: criteria to determine the number of shelter facilities that have • Holualoa E.S. low vulnerability buildings available higher vulnerability,taking • Waikoloa E.S.bldg D for refuge in the private sector. This into account the revised net • Waikoloa E.S.bldg E could result in a decrease in the shelter demand. • Konawaena E.S. number of persons that would report Perform a comprehensive screening to a public shelter. evaluation of public hurricane shelters and private sector buildings for possible use for refuge Hawaii County All-Hazard Assessment of The three to four facilities with the Proposed Project: Hurricane Shelters highest-ranked losses will be taken This detailed evaluation will This project will conduct onsite building to a detailed evaluation using Benefit be identifying priority construction as-built data collection for the Cost Analysis of potential mitigation buildings and providing the remaining 10 hurricane shelter buildings, measures. information necessary to using the more detailed DAGS- submit PDM grant standardized structural evaluation applications for three to four procedure that follows the criteria retrofit projects. established by the legislature Hardening of Waiakea High School Gym Waiakea High School Gym is a Last proposed for FY09 PDM Window,Door&Enclosure Retrofitting designated hurricane shelter,but has grant. Application requires Possible Roof&Framing connection glass doors and glass louvers further investigation to define retrofitting.When re-roofing a critical precise scope and cost,as facility,provide extra protection from well as developing the BCA water damage,check and refasten the roof sheathing. 5-19 Hawaii County Multi-Hazard Mitigation Plan Chapter•5:Hazard Analysis—Tropical Cyclones Project Description Status Hawaii Residential Safe Room Requirements for room construction NOAA and DBEDT features are given in the State sponsored research project to Building Code;effective by 2011 for develop and test wall those homes that do not provide assemblies rated for safe glazing windbome debris protection. room use. Hurricane Storm Surge Study(2008) Funded by FEMA for updating the Completed flood zones in the DFIRM on south and west coast Provide higher-grade poles for electrical PUC and utility to adopt use of Proposed Project distribution Hawaii topographic windspeeds for use with the National Electric Safety Code. Develop a Hurricane Loss Estimation . Expected hurricane risk levels Proposed Project: The Model(HLEM)software available for (i.e.,expected loss as a function of HLEM could provide Hawaii State and County planning return period)could be technically validated input on including state-of-the-art regionally- determined for a geocoded hurricane hazard and validated storm windfield modeling and building inventory database using vulnerability pertinent to tracking,topographic speedup modeling, the wind hazard analysis by State and County agencies. terrain category and building inventory Peterka combined with the Chock databases defined with detailed spatial topographic wind and building resolution,and regional building damage damage model. The Average and loss functions. State-of-the-art Annualized Losses due to could hurricane loss estimation requires be then calculated windstorms for regionally-validated storm windfield individual communities to modeling and tracking,topographic determine their risk relativity speedup modeling,terrain category and factors.This would allow an building inventory databases defined with objective ranking of hurricane risk detailed spatial resolution,and regional for regions or areas(such as building damage and loss functions. The census tract groupings),taking two NASA-sponsored projects have into account hurricane developed the core computational probabilities,site-specific wind components of what could be developed environment,and the building into Hurricane Loss Estimation Model inventory existent in each study (HLEM)software available for Hawaii region. State and County planning. Hurricane/MMS Upgrade for Hawaii Include the unique topographic wind USCOE-sponsored project for effects into the output of the model 2011 used as a tool for emergency response/evacuation decision- making,to allow identification of the topographically amplified wind speeds for any defined cyclone scenario. 5-20 Hawaii County Multi-Hazard Mitigation Plan