FLOOD01743 - Laserfiche WebLink

Home Browse Search

. . . Community Resnonse to the CWCB Desil!nation and Annroval Process The community was contacted initially by letter. Next attempts were made to contact by phone. No community official ever responded to repeated phone message left on the community's answering machine. ENGINEERING METHODS Hvdrolol!ic Analvsis Hydrology information for the streams with approximate floodplain delineations on Ramah's FHBM has been estimated in accordance with the CWCB's "Guidelines for Determining 100- Year Flood Flows for Approximate Floodplains" (Guidelines). The 1 DO-year flow for the streams with approximate floodplains can be estimated by utilizing the regression equation for Arkansas River Basin, subregion Ark-I. The equation is QlOO = t,564.98(A)""SJ9, where QlOO is the 100- year peak flow in cubic feet per second, and A is the upstream (contributing) drainage area in square miles. The regression equation is only valid for tributary streams having drainage areas between 25 square miles and 1,125 square miles. This equation is valid for Big Sandy Creek Creek. However, the drainage area for eastern and western unnamed tributaries to Big Sandy Creek is less than 25 square miles but larger than 0.5 square miles. Therefore, the U.S.G.S. publication entitled "Rainfall-Runoff Modeling and Preliminary Regional Flood Characteristics of Small Rural Watersheds in the Arkansas Basin in Colorado" is appropriate to use. Table 1 Estimated lOO-Year Peak Flows For Big Sandy Creek at Ramah, CO Stream Location Drainage Area (sq mi) tOO-Year Peak Flow in CFS Big Sandy Creek at 82.4 16,873 upstream town limit Western Unnamed Tributary 3.1 D.A. is too small for the near Ramah regression equation Eastern Unnamed Tributary 0.24 D.A. is too small for the near Ramah regression equation