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. . USFWS - Palisade/Grand Junction Stream Flow Analyses - DRAFT May 12, 1995 Page 19 Operation of the Cameo roller dam gates for winter power deliveries also affects calculated local inflows in the critical reach. Its believed a dip in the daily river hydrograph can be created when; 1) water is being stored behind the roller dam for diversion head, and 2) considering the increased travel time of diverting water through the canal versus travel time down the river channel. The degree of the dip depends on how much water is by passed while water behind the dam is being stored. A dip in the , Palisade Gage can be seen in the days prior to the beginning date of power diversions for 1994. A similar dip in the 27.5 Rd gage was not observed. It is believed that local precipitation at the time may have contributed additional local inflow above the 27.5 Rd gage masking the effects of storage behind the roller dam. In conclusion, it's believed actual local inflows are fairly consistent and some of the observed major drops are the result 'of miscalculations' caused by operations of the Grand Valley Project. V.4 River Inflows vs Local Inflow Since no well defined relationship was found between the 1991 or 1992 local inflow estimates and the river inflows to the Critical Reach, an analysis of the 1993 and 1994 data was not conducted. VI MEASURED LOCAL INFLOWS Richard D. Piland and Associates conducted a field investigation on September 8-9, to measure and OQserve surface returns to the critical reach from the Palisade Gage to the 24,5 Rd gage. Precipitation records indicate only traces of precipitation occurred the week prior to the field measurements, only .04 inches of rain on September 9. Thus, the inflows measured are primarily due to irrigation returns. Piland indicated inflows were measured when possible with appropriate stream gaging equipment and were otherwise estimated. In summary, Piland estimated the surface returns to be 118 cfs, of which 73 percent was measured and 27 percent estimated. Returns on the south side of the river (Orchard Mesa) totaled 35 cfs (30%) and 83 cfs (70%) returned from the north side (Grand Valley Canal and Government Highline). The largest inflow was measured at Indian Wash @ 28 Road, 32.6 cfs. ~ '. r..-" 27,~ - For comparison purposes, the calculated local inflow for September 8-9, averaged 217 cfs. This indicates that an additional 97 cfs returned to the critical reach as unmeasured surface inflows and groundwater returns. We believe the field measurements support the notion that local inflows are on the order of 150 to 300 cfs since more than half the flow appears to consist of surface returns.