COM 0176.043 2006-2008 - Laserfiche WebLink

Home

I have 22 years of experience in the design of highways, water systems, drainage systems, affordable and market housing subdivisions, commercial subdivisions, agricultural subdivisions, utility infrastructure and the preparation of Environmental Impact Statements. I have worked in the public sector for the County of Hawaii Department of Public Works and in the private sector for various firms so t am aware of issues and concerns regarding both public and private interests. T did not have time to review all of the additional amendments that were introduced to Bill 51 at the May ] ~ meeting. However, one amendment struck me as having extraordinary consequences for the agricultural industry. The amendment I am referring to is 27-20 (g). lt? Hawai`i Couutv agricultural subdivisions may exist in areas uphill from urban areas and may have severe flooding consequences: therefore, new :~¢riculturxl subdivisions shall comply with all requirements of Article 4, Section 27- 17-26 in that redirected flood channels shall meet base flood elevation levels and appropriate design and structures shall be provided to retain all rainfall up to a 100-vear storm event on the agricultural land on which the rainfall fell, In this regard I was just recently asked to consider storing all storm water generated from a 100-year, 24 hour storm on-site fora 9 acre community park project being constructed by anon-profit organization. The ]00-year, 24 hour rainfall in this location is approximately 7 inches. The results indicated that I would need a retention pond that was capable of storing 4.7 acre feet. In order to achieve this storage, one could build a one acre pond approximately 4.7 feet deep. The volume in cubic yazds of such a facility would be approximately 7,582 cubic yards. A rough estimate of the cost to construct the pond is $90,000. In addition, construction of a drainage system to pipe the water to the pond would be required. A really rough estimate of the cost of the piping and catch basin system is $200,000. The retention pond would require a drywell system to dispose of the water from the retention pond. My estimated cost for the drywells system is $60,000. The total rough cost for the system is $350,000. This does not include the loss of usable acreage I'or the park facility which in today's market could be $250,000 or more. I estimate that a conventional system using a 10 year storm with drywells would cost $40,000 to $80,000. If this park was located in Hilo where the 100-year, 24 hour storm rainfall is approximately 22 inches, the retention storage required would be 15.9 acre feet, over three times that of Kona. The number of catch basins and drywell and the pipe sizes would have to be much larger. This would entail substantially more costs and could make the project cost prohibitive, especially for anon-profit organization. My point is that I strongly advise the county council to seek the opinions of other engineering professional to confirm or dispute my estimates and then to analyze the economic impact to the entire island. I believe that adequate drainage is essential to this island. I am however concerned that we do not place an insurmountable economic burden on the use of land for agricultural purposes as I believe that agriculture is an extremely important land use.