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Last modified
1/26/2010 10:08:50 AM
Creation date
10/5/2006 4:11:22 AM
Metadata
Fields
Template:
Floodplain Documents
County
Teller
Community
Cripple Creek
Stream Name
Pony Gulch, Poverty Gulch
Basin
Arkansas
Title
Drainage Master Plan
Date
4/1/1992
Prepared For
Cripple Creek
Prepared By
GMS
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />SECTION IV <br /> <br />HYDROLOGY <br /> <br />Although typical storm drainage flows in the Pony Gulch and Cripple Creek watersheds are <br />of relatively low magnitude, the potential for damaging flows exists. These potentially <br />damaging flows will likely result from runoff caused by the very interne thunderstorms which <br />typical1y occur during summer and fall months. As development within Cripple Creek <br />increases, existing runoff patterns are likely to change resulting in an increase in peak flows. <br />Therefore, it is necessary to estimate storm drainage flows for the watersheds in projected, <br />fully developed conditions. Those estimated, fully developed peak flows are then used in <br />the hydraulic analysis of existing and proposed structures. <br /> <br />A. General <br /> <br />As previously stated, the United Slates Department of Agriculture Soil Conservation <br />Service, in conjunction with the Colorado Waler Conservation Board is preparing a <br />Floou Plain Management Study for the City of Cripple Creek. Thai study is <br />scheduled to be completed in October 1992. It i> intended that this Drainage Master <br />Plan supplement the Hood Pl:\in Management Study, not recreate the information <br />contained within that study. As the final Flood Plain Management Study will not bc <br />available until October 1992 and potential future development is pending, awaiting <br />the results of this Drainage Master Plan, the Cripple Creek City Council authorized <br />GMS, rnc. to commence preparation of this ma,;ltr plan prior to completion of the <br />Flood Plain Management Study by the SCS. <br /> <br />On January 16, 1992, OMS, Inc. received a copy of the SCS's preliminary hydrology <br />report, lhe first majur step ill Jt~du]llllcnt of the Flu(lJ Plain ~:anagemcnt StuJy. <br />The preliminary hydrulogy report defined the limits of the watershed's major <br />drainage basins as they affect the drainageways within the City of Cripple Creek. <br /> <br />1\'-1 <br /> <br />That report also determined rainfall intensities and point rainfall depths for various <br />storm freql.lendes. In addition, the report determined preliminary ]leak discharge <br />rates al designated design points within thedty. <br /> <br />B, <br /> <br />Methodolo~y <br /> <br />During preparation of the preliminary hydrology report and the final Flooll Plain <br />Management Study, the SCS will utilize the Soil Conservation Service Method to <br />detennine peak runoff rates from the various drainage basins. The SCS Method <br />utilizes a computer mollel, called TR-20, to route storm water runoff through basins <br />and associated drainageways anll determine peak discharge values at various <br />designated design pOilllS. The procedure is accurate for larger ba~ins but as basin <br />size llecreases (less than 200 acres) some precision is lost. Also, the procedure is <br />computcrdcpcnllent and tedious when used to analyze numcroussma II subbasins. <br />The approximate limits of the drainage basins analyzed by the SCS in preparation <br />of their preliminary hydrology repoT! can be seen on Exhibit 2, "Drainage Structures" <br />A peak llischarge rate has been determined by the SCS at the lower end of each of <br />the basins shown on Exhibit 2. <br /> <br />A review of Exhibit 2 also shows that numerous urainage facilities exist within each <br />of the drainage basins as defined by the SCS. To analyze the existing drainage <br />facilities, it is necessary to determine a peak runoff rate at each structure. To <br />perform that task, the drainage basins defined by SCS were divided into smaller <br />subbasins with a llesign puint occurring at each structure. Exhibit 1, "Drainage Map" <br />shows tho; limits of the SCS drainage basins, lhe smaller subbasins within each basin <br />and a design point number at each exi~ting structure or point where runoff h:avt:s tht: <br />hasin or subbasin. <br /> <br />Eaeh major urainagt: basin is ucfino;d on the exhihits with a 3-letter de,;cription. The <br />firsl 2 Icller, define the stream or lributarv to which the basin ('onlrihules, (i.e., PG <br /> <br />IV-2 <br />
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