03/12/1996 Minutes - Laserfiche WebLink

Home Browse Search

` t" 23379 Sharon Drive North Olmsted, OH 44070 March 11, 1996 Dear Planning Commission Members, You are to be commended for your admirable efforts in addressing the many delicate issues surrounding the Bridgeport Development. Your genuine concern for the residents, both existing and potential, is appreciated. As a registered civil engineer in the State of Ohio who has spent his career designing wastewater treatment and conveyance systems, I need to express my genuine concern over Bridgeport Development. In particular, I believe that the retention basin is seriously undersized. I do not have access to all the engineering data and drawings. However, I was able to examine two drawings in the current Western Reserve drawing set, and have made a few engineering calculations. Suppose you had the following conditions_ Assume Rice Ditch is completely dry (it almost never is). Assume further that a sudden, heavy storm began, and all the pipes leading into and out of the storm water retention basin were instantly to flow full under the force of gravity. Under these circumstances, the storm water retention basin would fill in about 50 minutes. How likely is it that basin is undersized? In my professional opinion, very likely, since the data used to size the basin is out-of-date. According to the Climate Analysis Center, the National Weather Service, the National Oceanic and Atmospheric Administration, and the U.S. Department of Commerce, the rainfall data presented in North Olmsted's "Storm Water Management and Urban Sediment Pollution Abatement Systems" under- predicts rainfall amount by up to 25%. Thus, the 10% safety factor built into the North Olmsted code still falls as much as 15% shy of where these Federal Agencies say it should be. Also, I used a digital planimeter to calculate the volume that this basin can store. My calculations show that the effective volume of the basin is roughly 318,000 cubic feet. The last time I heard about this issue, the volume of the storm water retention basin was 414,000 cubic feet_ According to my calculations, the size of the basin as shown on the Western Reserve drawings is about 30°/a less than what was expected. How often will this basin flood? This is difficult to predict accurately. Based on the most recent information rainfall data available, and using the more conservative numbers above, this basin is estimated to flood out once every twenty-five years or so.