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<br />002256 <br /> <br />A Flood Hazard Analysis of Coal Creek and Rock Creek was requested by <br />Boulder and Weld Counties, and the Urban and Drainage Flood Control <br />District through the Colorado Water Conservation Board in 1974. This <br />analysis, completed in 1976, by the Soil Conservation Service, delineated <br />the IDO-year and 500-year flood plains along Coal and Rock Creeks. <br /> <br />Problems and Needs <br /> <br />The Flood Hazard Analysis study indicated that a potential flood of the <br />100-year frequency magnitude would inundate portions of the residential <br />and commercial developments in the communities of Erie, Lafayette, <br />Louisville, and Superior. The largest concentration of damage would occur <br />in Erie where approximately 90 homes and 75 mobile homes are located <br />within the 100-year flood plain. The study also indicated that 2,466 <br />acres (986 ha) of land are subject to inundation by the 100-year flood. <br /> <br />Municipal and industrial water supply problems in the watershed have not <br />been solved. ~owever, since the Bureau of Reclamation is studying this <br />problem it was not addressed during this reconnaissance study. <br /> <br />Alternatives Considered <br /> <br />Six basic alternatives were evaluated. These are: <br /> <br />1. Two floodwater retarding structures - one each on Coal and Rock <br />Creeks. The Coal Creek floodwater retarding structure is located west <br />of Superior. The Rock Creek floodwater retarding structure is located <br />approximately two miles southeast of Superior, south of the Denver- <br />Boulder Turnpike, on Rock Creek. <br /> <br />I <br /> <br />2. A floodwater retarding structure northeast of Lafayette on Coal <br />Creek. ' <br /> <br />3. A floodwater retarding structure on Coal Creek, south of Erie. <br /> <br />4. A floodwater diversion dike east of Erie. <br /> <br />5. Flood proofing individual buildings in the flooded area. <br /> <br />6. A no-project-action alternative. <br /> <br />Figure 1 is a map showing the location of the alternatives. Elements of <br />each alternative are shown in Table 1. <br /> <br />Alternative #1 consists of two floodwater retarding structures. The Coal <br />Creek Floodwater Retarding Structure (west of Superior) is a class C <br />structure with 25 square miles (64.75 sq. km) of drainage. It is a 65 <br />foot (19.8 m) high dam with 2,084 acre feet (2,570,614 m3) of storage <br /> <br />2 <br /> <br /> <br />~. ~,,<--cn-"'--"-~'.'~' -_ -.... --'-:~"'''-_ ,--;-,,,.., '_"""-~~"""'''''''--~~''.~~', ._~ ~...~. '.l~~::.- _ <br />