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npcrDTDTTOM nF ADC-A The study was limited to the upper Colorado River and a major tributary, the Gunnison River. Fig. 1 of the Colorado River, one of the major drainages in Colorado has its headwaters on the Continental Divide near the town of Grand Lake, Colo- rado. The only main stem dams in this upper area are Granby and Shadow Mount- ain, located near the headwaters. Nearly every major tributary has one to several dams. The Gunnison, also under study, has three main stem dams and several dams on its tributaries. The first major dam in the drainage was constructed in 1937 while the first irrigation diversion probably occurred prior to 1900. From this, it is evident that the Colorado and Gunnison Rivers have not been subjected to natural flows for decades. The specific area of study on the upper Colorado River was restricted to the 130 miles of river between the mouth of DeBeque Canyon and Moab, Utah. The river throughout the study area is large, slow moving and usually turbid. At the head of DeBeque Canyon, the mean flow of record is 3,775 c.f.s. with a maximum of 22,500 c.f.s. and a minimum of 1,050 c.f.s. (USGS 1974). Between Cameo, Colorado and the Utah state line the river falls 448 feet or an average fall of 7.8 feet per mile. The drainage area at this point is 7,320 square miles with diversions for irrigation of approximately 158,000 acres occurring upstream. Irrigation return flow greatly adds to the tur- bidity and an already high salt content. The area of study on the Gunnison River was located between the town of Delta, Colorado and its confluence with the Colorado River near the town of Grand Junction, Colorado. This section of river, approximately 50 miles in length, drops an estimated 380 feet or an average fall of 7.2 feet per mile. Mean flow of record as measured at Whitewater is 2,562 c/f/s/ with historic flows ranging between 35,700 and 106 c.f.s. (USGS 1974) (3) ;,441