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WSP07965
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Last modified
1/26/2010 2:29:36 PM
Creation date
10/12/2006 2:41:53 AM
Metadata
Fields
Template:
Water Supply Protection
File Number
8446
Description
Cache La Poudre Project
State
CO
Basin
South Platte
Water Division
1
Date
7/1/1983
Title
Cache La Poudre Project Study and Related Correspondence
Water Supply Pro - Doc Type
Report/Study
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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />amount imported into the upper basin through the transbasin import facilities <br />to the west. The consumptive uses and effects of regulation assumed to be <br />minor were not included in the adjustment. The resulting flows are plotted in <br />Figure 1II-6. <br /> <br />The de.ived annual native flows exhibit the same general trends as do <br />the recorded annual flows discussed earlier in this Chapter. The early pe- <br />riod, prior to 1905, is "wet". Then the records move through a transition to <br />a dryer period beginning in 1925. The estimated native flows for the dryer <br />period, represented by the 56-years from 1925 to 1980, averaged 271,000 acre- <br />feet per year. <br /> <br />4. Se1ection of the Hydrologic Study Period <br /> <br />It appears that the Cache la Poudre River is still in a period of a <br />long cycle which is "dryer" than, normal. As long-term climatic changes are <br />not predictable, it is prudent to select the long, dry period as the norm for <br />any study. Thus, the statistics for the estimated native flow at the mouth of <br />the canyon from 1925 through 1980 have been assumed in this study to represent <br />what future native flows from the upper basin will be. <br /> <br />Since a 56-year record is exceedingly long for the purposes of recon- <br />naissance level reservoir operation studies, a shorter period, 1949 through <br />1971 was selected as representative of the long term conditions. Called the <br />hydrologic study period, this 23-year portion of the total record also has an <br />average annual estimated native flow of 271,000 acre-feet. Along with the <br />average annual flow, the shorter 23-year hydrologic study period exhibits <br />other statistical characteristics similar to the longer 56-year period. The <br />hydro log ic st udy per iod also contains the dr iest year of recor d, 1954, for <br />which the estimated native flow at the mouth of the canyon was only 121,000 <br />acre-feet, and the driest four consecutive years of record, 1953 through 1956. <br /> <br />5. Derivation of Month1y Native F10ws <br /> <br />I <br />1 <br />I <br /> <br />Native streamflow at streamgaging stations in the upper basin and at <br />all existing and potential damsites considered in this study were estimated <br />for the hydrologic study period by correlation with the flow records at the <br />streamgages within the basin. The correlations were done using HEC-4, the <br />U.S. Army corps of Engineers' generalized computer program for streamflow <br />s imulat ion. <br /> <br />I <br />I <br />I <br /> <br />The native streamflows were derived as monthly flows and extrapolated <br />as necessary to the length of the study period. In determining the stream- <br />flows at the existing reservoirs and potential damsites, consideration was <br />given to the relation between annual precipitation; the size, shape, orienta- <br />tion and elevation of the watershed; and direction of storm movement. The <br />correlations with the HEC-4 model produced monthly values for the length of <br />the study period for each existing reservoir and potential damsite. The <br />monthly flow records and results of these derived streamflows are available in <br />computer files. <br /> <br />1II-3 <br /> <br />I <br />
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