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<br />. <br /> <br />. <br /> <br />. <br /> <br />ENGINEERING METHODS <br /> <br />Hvdroloeic Analvsis <br /> <br />Hydrology information used for streams with detailed floodplain delineations in the Colorado <br />Springs FIS is discussed in Section 3.1 of the FIS'. Hydrology information for the streams with <br />approximate floodplain delineations in the Colorado Springs FIS' has been estimated in accordance <br />with the CWCB's Guidelines for Determining IOO-Year Flood Flows for Approximate <br />Floodplains (Guidelines). Depending on the drainage area of the upstream (contributing) <br />watershed, the 100-year flows can be estimated either by using a regression equation included in the <br />Guidelines, or by using a USGS publication approved in the Guidelines. A copy of the Guidelines <br />can be obtained by writing to the Colorado Water Conservation Board, Flood Control and <br />Floodplain Management Section, 1313 Sherman Street, Room 721, Denver, Colorado, 80203. <br /> <br />The 1 DO-year flow for each of the streams within the City of Colorado Springs with approximate <br />floodplains can be estimated by utilizing one of two regression equations for the Arkansas River <br />Basin. The City of Colorado Springs falls within the boundaries of two separate subregions, <br />subregion ARK-4a and subregion Ark-4b. <br /> <br />· Subregion ARK,4a covers the western portion Colorado Springs and adjacent areas of El <br />Paso County. It covers areas west of Monument Creek and the reach of Fountain Creek <br />downstream of Monument Creek. It includes Green Mountain Falls, Manitou Springs and <br />the portions of Monument, Palmer Lake, Colorado Springs and Fountain west of Monument <br />Creek and Fountain Creek. <br />· Subregion 4b covers the eastern portion of Colorado Springs and adjacent areas of central <br />EI Paso County, east of Monument Creek and Fountain Creek. It includes the portions of <br />Monument, Palmer Lake, Colorado Springs and Fountain that are east of Monument Creek <br />and Fountain Creek. <br /> <br />Figure I, presented in the Appendix of this report, displays the subregional boundaries for the City <br />of Colorado Springs and adjacent areas of unincorporated EI Paso County, The regression <br />equations are as follows: <br /> <br />Subregion ARK.4a: QIOO= 1408.2(At.654 (For I<A<26) (Westernfoothills) <br />Subregion ARK-4b: QIOO = 1343.4(A)os78 (For 4<A<75) (Foothills in central county) <br /> <br />The QlOo is the 100-year peak flow in cubic feet per second, and A is the upstream (contributing) <br />drainage area in square miles, The Guidelines regression curves for subregions ARK-4a and Ark- <br />4b are also presented in the Appendix. Each equation has a range of applicability, based on the <br />drainage area of the upstream watershed: <br /> <br />3 <br />