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ENGINEERING METHODS Hvdrololric Analvsis Hydrology information for the approximate floodplain delineation on the Akron FHBM for the Northeast Drainage and its tributaries and for the tributaries to the Southwest Drainage has been estimated in accordance with the CWCB's Guidelinesfor Determining lOO-Year Flood Flowsfor Approximate Floodplains (Guidelines). The lOa-year flow for the Northeast Drainage (only downstream of its confluence with the North Tributary) and the Southwest Drainage can be estimated by utilizing the regression for the Republican River Basin. The equation is: Q,oo = 289.1 (A)o.667 In that equation, Q,oo is the lOa-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 I square mile and 1300 square miles. This equation is valid is valid for the Northeast Drainage downstream of its confluence with the North tributary and for the Southwest Drainage. Because the tributaries to these two drainages and the Northeast Drainage upstream of its confluence with the North tributary all have drainage areas less than I square mile, the regression equation is not valid for those drainages at those locations. The drainage areas for all of the mapped drainages in Akron are listed in Table I below. The estimated flows for the Northeast Drainage and the Southwest Drainage are listed below in Table 2. The regression equation for the Republican River Basin is not valid for the tributaries to the Northeast Drainage and the Southwest Drainage that are mapped on the FHBM, or for the Northeast Drainage upstream of its confluence with the North tributary, which is also mapped on the FHBM. There is no procedure currently endorsed by the CWCB for estimating hydrologic values for streams within the Republican River Basin with drainage basins smaller than I square mile. In order to assure that flood risks on those tributary drainages and on the upper portion of the Northeast Drainage are appropriately taken into account, the Town of Akron will have to require a detailed hydrologic analysis for any development activities along those streams. Figure 1, presented in the Appendix at the end of this report, displays, in map form, the entire Republican River Basin. The regression curve for the Republican River Basin is included in the Appendix as Figure 2. Tables I and 2 below provide information about the drainage areas of the various drainages and the estimated lOa-year peak flows for the Northeast Drainage and the Southwest Drainage at the respective downstream corporate limits. 4