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<br />. <br />. <br />. <br />. <br />I. <br />:. <br />. <br />I. <br />i. <br />. <br />. <br />. <br />. <br />. <br />:. <br />i. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />I. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />Ie <br />. <br />. <br />. <br />. <br />. <br />. <br />'. <br />. <br />. <br /> <br />Wash <br /> <br />Master Plan <br /> <br />Phase I: Watershed Floodplain Delineation <br /> <br />rates to more closely match observed rates, Detention elements (reservoirs) were developed <br /> <br />behind culverts that did provide storage, Examples of these situations include 1-70 and the <br /> <br />Government Highline Canal. When it was determined that the presence of a detention element <br /> <br /> <br />was appropriate, a stage-storage-discharge relationship was developed to model the reservoir. <br /> <br />Contours provided in the GIS mapping were used in the computation of available storage, The <br /> <br />stage-storage-discharge relationship for each reservoir is shown in Table 5, A schematic of the <br /> <br />HMS model structure, including storage and diversions, is provided in Figure 3, Figure 4 shows <br /> <br />the location of the HMS model nodes on an aerial photograph of the watershed, A more detailed <br /> <br />summary of the hydrologic analysis is provided in Appendix 2. <br /> <br />4.5.1 CWCB Floodplain Storage Criteria <br /> <br />Inadvertent storage is a critical component of the complex hydrology and hydraulics within the <br /> <br />Bosley Wash Basin, The use of this storage is inconsistent with Rule 7 of CWCB's Rules and <br /> <br /> <br />Regulations for the Designation and Approval of Floodplains in Colorado, Given the nature of <br /> <br />this basin, the County and GJDD believe that the watershed cannot be accurately modeled <br /> <br />without incorporating storage features, Discussions with CWCB indicated that the inclusion of <br /> <br />these storage elements is appropriate in this case and that this application represents an <br /> <br />acceptable deviation from their standards, <br /> <br />4.6 Hydraulic Summary <br /> <br />As expected, the results of the hydrologic modeling'indicate a high variability in the level of <br />flood hazard within the watershed, Table 6 presents a summary of the results of the hydrologic <br />analysis which are also presented graphically in the discharge profile provided as Figure 5, <br /> <br />.u <br /> <br />__',~?,1!.tijf:>~~~'Z"^-~~C;,\'~':- <br /> <br />~ <br /> <br />@"{ <br /> <br />:)~_~"~"J..~_f!_t:_ \ <br />/.V <br />~';~_~.;;[;;::-1:.\~ <br /> <br />. <br /> <br />Page 16 <br />