Laserfiche WebLink
<br />HYDROLOGY REPORT <br />FLOODPLAIN INFO~~;TION STUDY <br />UXCO~WAHGRE RIVER AND TRIBUTARIES <br />Ouray County, Colorado <br /> <br />General Problem <br /> <br />The objective of this report is to furnish hydrological estimates for <br />flood runoff in the Uncompahgre River and its tributaries near Ouray, <br />Colorado. The range of basin areas under consideration range from 1.3 <br />to about 200 square miles. Gaging records are fairly good in the area. <br />Basins are steep and rocky with elevations ranging from 7,500 to over <br />13,000 feet. <br /> <br />As it is required to develop estimates for 10, 50, 100 and 500 year flood <br />events we face the problem of trying to synthesize best estimates for an <br />extremely complex hydrological phenomena. Fortunately, in addition to <br />the several gaging records recently completed, a USGS/CWCB report was <br />recently completed providing regional equations for the area (Ref. 1), <br />C,;mp, Dresser and HcKee Consulting Engineers recently completed an anal- <br />;:sis of gaging records applicable to San Miguel County, near to the area <br />'mder consideration here (Ref. 2), and the SCS published a guide spec if- <br />c ca.lly for calculating peak flows in Colorado (Ref. 8). <br /> <br />Generally, the methods of Hater Resources Council Technical Bulletin No. <br />17 have been followed in this study. <br /> <br />The general approach adopted has been to rely on USGS data and the COM <br />report for larger basins and on rainfall-runoff calculations for the smaller <br />basins. This procedure is explained in more detail in the following sec- <br />tions. <br /> <br />Discharge Data Set <br /> <br />T~1e basic data available \"as from USGS water supply papers (Ref. 1, 3, 4). <br />.~"alyses had been conducted using the Log-Pearson Type III method, adjusted <br />with the regional equations to account for persistence in the periods of <br />r.cord available (Ref. 1). Values in Reference 1 reflect la, 50, 100 and <br />SOO jear values derived in this manner. These are shown for the gages <br />s"lected in Table 1. Also shown are the periods of record and values cal- <br />ctrlated from regional equations given in Ref. 1. <br /> <br />In Reference 2, an approach was taken to consider the floods as a mixed <br />pcpulation set (some from L-ainfall, SOi.1e from sno\~Omelt). This approach <br />has some merit but introduces perhaps more questions than it answers. A <br />fllrther discussion of these points will come in a later section. <br /> <br />f),ita frcm Ref.~rence 2 is shm-in ~\'ith the comp8.rable figures in Table 2. <br />T:~2 values will be described later. <br />