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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 />= Pony Gulch, SS = Second Street Tributary, etc.) The third letter in the <br />description is the major basin designation from the SCS preliminary hydrology report. <br />Each subbasin is defined by the 3-letter ba.~in designation previously described <br />followed by a number (i.e., 1,2, 3, etc.). All2-digit design point identifications are <br />locations where peak discharge rates have been determined by the SCS. All 3-digit <br />design point identifications are locations where peak runoff rates have been <br />determined in this Drainage MasterPlan. <br /> <br />Exhibit 1 shows that numerous small subbasins exist throughout the corporate limits <br />of Cripple Creek. To analyze each of the small subbasins within the corporate limits <br />using the Soil Conservation Service Method would become very time-com;uming and <br />accuracy would be lost due to the small size of the subbasins. Therefore, another <br />method for determining peak runoff from these small subbasins was researched. The <br />'Teller County Drainage Criteria Manual" states that the Rational Method should be <br />used to analyr.e peak flows from drainage basins containing less than 20 acres. This <br />method. developed in the late 1800's ha.~ been shown to yield satisfactory results in <br />small basins when properly applied. The "City of Colorado Springs/EI Paso County <br />Drainage Criteria Manual" recommends use of the Rational Method to analyze peak <br />nows from drainage basins containing less than 100 acres. The "Denver Regional <br />Council of Governments Drainage Criteria Manual" recommends use ofthe Rational <br />Method for analyzing peak flows from drainage basins containing less than 160 acres. <br />The Rational Method is significantly more user friendly than the Soil Conservation <br />Service Metholl,pruvides acceptable re,ults when properly applied andwillbenluch <br />simpler to implement for future developers. The Rational Method will be discussed <br />in detail later in this report. <br /> <br />c. <br /> <br />Utilization of the Ratinnal Method to determine storm water runoff within the <br />corporate limits of Crippie Creek wa, di,cussed with representatives of the Soil <br />Conservation Service and the Colorado Water Con~crvation Bourd. ^ consensus was <br />reachcll as to use of this method as long a.~ results correlated reasonably wdl with <br /> <br />IV-3 <br /> <br />results obtained by the SCS when analyzing the overall watersheds. Prior to <br />performing a detailed hydrologic analysis of the subbasins within Cripple Creek on <br />a projected full development condition, peak runoff at the various design points was <br />determined based on e;o;isting development. This procedure was undertaken to <br />determine how closely results of the Rational Method would correlate with results <br />obtained by the SCS. Table 1 in Appendix B, "Hydrology: Pony Gulch-Existing <br />Development" and Table 2 in Appendix B, "Hydrology: Cripple Creek - Existing <br />Development" present the results of this analysis. It was determined, at design points <br />common between this Drainage Master Plan and the SCS preliminary hydrology <br />report that peak discharge rates were within 5% in most instances. This correlation <br />was doser than anticipated and shows that the Rational Method will yield satisfactory <br />results where properly applied. Therefore, the Rational Method as described within <br />this master plan shaH be used to determine peak runoff rates from drainage basins <br />and subbasins within the corporate limits of Cripple Creek. It is recommended that <br />the city adopt this methodology as it's standard criteria. <br /> <br />Rational Method <br /> <br />The Rational Method relates peak runoff to drainage area, rainfall intensity, and <br />basin surface characteristics by the formula: <br /> <br />Q= C;o;ixAxC( <br /> <br />Where: <br /> <br />Q = peak runoff rate, in cubic feet per second (CF5); <br /> <br />C = runoff coefficient representing proportion of total <br />precipitation which appears as runoff; <br /> <br />= average rainfall intensity in inChes per hour for a <br />duration equal to the runoff time of cone cot ration; <br /> <br />IV-4 <br />
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