COM 0176.123 2006-2008 - Laserfiche WebLink

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July 3, 2007 Honorable Pete Hoffmann, Chairperson Hawaii County Council 333 Kilauea Avenue Second Floor Hilo, Hawaii 96720 Testimony on Bi11 51, Draft 5 Proposed Amendments to Chapter 27 of the HCC Honorable Chairperson Hoffmann and Members of the Hawaii County Council, I attended the ad hoc committee meetings that were held on June 22 and June 26 as a member of the public I came away from those meetings with the feeling that there was still a great deal of confusion about urban drainage design and flood plain management and the regulations that govern each of these items. I am especially concerned that some believe there is a huge inadequacy in the design storms currently being used to size drainage systems. Some of the confusion seems to stern from a lack of understanding of the difference between urban drainage system design and flood plain management. According to the Standard Handbook for Civil Engineers. Third Edition, Frederick S. Merritt, Editor, McCmaw-Hi1lBook Company, 1983, "Flood problems and surface drainage, as concerns of community and regional planning studies, differ in degree and severity. The principal concern with flooding is the desire to avoid injury and loss of life and reduce property damage caused by major floods (those having a recurrence interval of 25 to 100 years). Surface-drainage systems, on the other hand, aze primarily concerned with convenience and providing access to property during relatively minor storms (those having recurrence interval of 2 to 10 years.)" The County of Hawaii currently mandates a 10 year storm be used to size surface drainage facilities which is at the high end of the desi~ storms used by most communities. Hawaii County uses the 100 year storm to size systems designed to protect against major floods. This also is also a conservative storm. It seems that some members of the County Council may be confusing urban drainage design and flood plain management design. 1 urge you to consult with the Department of Public Works and other professional civil engineers before assuming that the current codes and standards are inadequate. Based on my 17 years of designing drainage systems in the County of Hawaii I would say that the current requirements of Chapter 27 and the County of Hawaii Storm Drainage Standards are significantly above average and more than adequate. I have prepared drainage plans and studies in many different parts of the Country and my professional opinion is that Hawaii County has some of the most conservative codes I have come across. For example, Chapter 27 does not allow a rise in the base flood elevation. FEMA allow a rise of up to one foot. Many communities that I have worked in also allow the one foot rise. Hawaii County is also the only county I have ever worked in that requires all increase in the 10 year storm runoff to be disposed of onsite. Most communities only require detention and many communities also use storms of lesser magnitude such as the 2 year or 5 yeaz storms. I have been told that some communities in California require the 25 year storm for certain drainage conditions. This is also the case here in Hawaii where under certain conditions, the 25 or 50 year storm is used to size culverts crossings of some roads.