09-17-07 Meeting of Drainage and Flooding Committee

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tion standards in force in several watershed communities were inadequate to prevent increases in downstream flooding. Finally, the study identified significant areas of natural storage upstream. If this storage were to be removed, flood damages in our watershed would go up by 50% or more. Recognizing their vulnerability, downstream communities requested the cooperation of all the towns of the watershed to continue to work together to prevent flooding from becoming worse. Fortunately, communities responded positively; the study had driven home the fact that flooding is a watershed problem that begins when the first raindrop hits the upland. MULTI -OBJECTIVE GOALS Our Committee first established the following goals that clearly lay out the multi -objective nature of our work: 1. Reduce flooding and minimize streambank erosion in the Butterfield drainage basin. 2. Protect the storm and floodwater capacities of natural detention areas and protect wetlands. 3. Preserve public open space to increase recreational opportunities (including trails), protect and enhance natural resources, and improve the environment of communities and neighborhoods. 4. Improve stream maintenance to maximize natural resource benefits and aesthetics. 5. Improve the quality of water in Butterfield Creek and its tributaries. 6. Achieve a mutually supportive, basin -wide management and regulatory framework for develop- ment activities affecting Butterfield Creek. TAKING ACTION With goals adopted, our next step was regulatory. We needed to address those critical issues pointed out by the engineering study. The Butterfield Creek Model Floodplain and Storm - water Management Code was published in November, 1990 and has since been adopted by all five of the critical upstream communities of the watershed. Here are some highlights of our model code: • We are requiring that the storage capacity of those all important natural storage areas be main- tained. Because portions of these areas are outside wetlands and floodplains, they were previously unregulated. Now, any construction on these properties will require compensatory storage to make up for lost natural storage. This is in addition to the usual detention requirements. • Detention requirements have been significantly strengthened. We have beefed up detention standards to match real world conditions. Release rates must meet 100-year storm limits of 0.15 cubic feet per second per acre and two-year storm limits of 0.04 cubic feet per second per acre. The two-year requirement is aimed at stabilizing runoff rates to prevent increased erosion of downstream channels. • The adverse water quality effects of development are addressed by requiring effective soil erosion and sediment control, encouraging "natural" drainage practices such as swales and vegetative filters, and specifying detention basin designs which enhance pollutant removal. • Our regulatory floodplains have been expanded to coincide with those demonstrated by the engineer- ing study. The revised mapping has also been adopted at our request by the State regulatory agency. • We have limited uses in the floodway, allowing only public flood control, public recreation and open space, crossing roads and bridges. Success Stories 11