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<br /> <br />(3) Hypothetical floods developed and routed by the Bureau of Reclama- <br />tion, (for the report on flood control benefits of the Curecanti Unit). <br /> <br />(4) 100-year and standard project floods developed and routed by the <br />Sacramento District (for the 1973 flood plain information report on Grand <br />Junction) . <br /> <br />(5) Bureau of Reclamation's objective flow of 15,000 cfs above Delta. <br /> <br />It was impossible to satisfy all the above criteria and still maintain <br />a consistent level of protection at the two gages. It should be noted that <br />the Bureau and the Corps routings (items 3 and 4 above, respectively) were <br />based on different criteria for reservoir operation. The Bureau routings <br />were based on low to moderate releases prior to peak outflow at Blue Mesa <br />Reservoir, and the Corps routings were based on maximum releases. Consider- <br />ing the reservoir operation record, it is probable that actual operation <br />during high flows would be somewhere between those hypothetical operations. <br />Future studies of operation of the reservoir are to be made by the Sacramento <br />District. <br /> <br />The frequency curve adopted for the "below Gunnison Tunnel" gage is <br />sho"" on Chart 15. It satisfies the established criteria as it passes <br />through the regulated flow data and the hypothetical floods in a "best fit" <br />manner. The June 1970 peak flow of 9,600 cfs was considered a high outlier. <br />Flows at other gages in the basin indicate a frequency of less than once in <br />10 years. The Bureau of Reclamation indicated that releases from the Blue <br />Mesa Reservoir were not in accordance with nOILlal operating procedures and <br />that had they been, the peak outflow would have been significantly less. <br /> <br />The adopted peak flow-frequency curve for the "near Grand Junction" <br />gage is shown on Chart 16. Although the curve lies above the regulated <br />flows of record and the Corps routed floods (item 4 above), it satisfies the <br />other criteria. The curve was developed (1) to intersect the flow of 11,000- <br />12,000 cfs at an exceedence interval of 2 to 3 years (flows for 3 of the 11 <br />years since initial regulation are in this range, and flows observed at <br />other gages in the basin for these 3 years indicate a similar frequency), <br />and (2) to provide protection equal to or less than that shown for the "below <br />Gunnison Tunnel" gage. <br /> <br />c. Ungaged Sites on the North Fork Gunnison and Gunnison Rivers. Peak <br />flow-frequency curves for the ungaged sites on the North Fork Gunnison and <br />Gunnison Rivers were developed by computing the difference between the curves <br />for natural and present conditions for the "near Somerset" and "below Gunni- <br />son Tunnel" gages and subtracting this difference from the curves for natural <br />conditions at the ungaged sites. The resultant frequency curves are shown <br />on Charts 17-25. <br /> <br />12. Results. Peak flows of the 10-, 50-, 100-, and SOD-year floods at the <br />selected index points are shown in Table 4. <br /> <br />12 <br />