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SECTIO:"l! I SUMMARY AND RECOMMENDATIONS A. Pumo,e and Scope The purpose of this sllldy was to prepare a detailed Drainage Master Plan for the City of Cripple Creek. This Drainage Master Plan is intended to supplement but not recreate the information contained in the Flood Plain Management Study currently being prepared by the U.S. Department of Agriculture Soil Conservation Service. This master plan will make recommendations for improvements to existing drainage facilities within the City of Cripple Creek and provide a guide for storm drainage planning and design within the city. This ma.,ter plan will also establish drainage criteria and standards for use by owners of undeveloped property who wish to develop said property. This report i, intended to serve as a guide for addressing existing drainage problems as well as the coordination and implementation of drainage improvemcnts within the City of Cripple Creek as development oCOlrs. It is hoped that this document will assist city officials, potential developer, and the general public in making sound decisions relating 10 land use and drainage improvements within the city's corporate limits. , I I I I I I B. Storm Water Runoff Conditions The watershed, contriouting runoff to drainage facilities within the City of Cripple Creek encompass approximately 2,100 acres. Topography within the watersheds are characteri,tic of mountainous areas with steep slopes and well defined drainage channels. Soil conditions within the hasin vary with most of the soil groups having llreilltivelyhighrunoffpotential. Portions of the oasin are presently at or near full development while other areas have not been significantly improved to date. I-I This study has attempted to rationally analyze the variuus factors affecting storm water runoff as they relate to the corporate limits of Cripple Creek under fully developed conditions. Available land use information, both exi,ting and proposed, has been considered in developing peak runoff rates used for preliminary storm drainage facility design purposes. Hydrologicca1culations have been based on the 24-hour duration storm event. Hydraulic analyses were based on peak runoff resulting from the tOO-year return frequency storm when the tOO.year storm produced peak flow rates greater than 300 cubic feet per second (CFS). \\!hen peak flow rates from the lOO-year storm resulted in flo"""!; less than 100 CFS, peak flow rates resulting from the lo.year storm were utilizcd. In cases where the tOO-year peak flow rate was between 100 CFS and 300 CFS, the design flow rate used in the hydraulil;'analysis was selected based on the evaluation ofpotenti aldamageresulting from runoff in excess of that generated by the lO-year storm. Methodology utilized in the hydrologic and hydrau1ic analyses conducted as part of this study conform with acccptcd engineering practices. It is therefore felt that this report presents a technically adequate and economically sound master plan for present and future drainage improvements within Cripple Creek. c. Development of Drainaee Improvements N; part of the master planning process, specific drainage improvement, have been proposed. In arriving at these specific reoommendatiolL~, numerous a.~sumptiolL~ had to be made. Variations from assumed developmem pallems, changes in timing of implementation of devclopmem plans, etc. could significantly affect Storm water runoff rates and thercfore the size, typc andjm location of drainage f aci1ities required to safely convey these flows. The desire of developers to incorporate drainage improvements which may be more compatible with their development plans couldalsoleadtomodificationsorrevisionsofthespecificproposaIs contained in Ihisreporl. 1-2