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. . USFWS - Palisade/Grand Junction Stream Flow Analyses - DRAFT May 12, 1995 Page 3 ' si,gnificant short term variances in calculated local inflow due to travel time and bank storage of peaking' hydro graphs caused by storage and release of storage water behind the dam. This cause should be added to local precipitation events, gage rating problems, icing and inaccuracies in flow measurement. 5. Local inflow to the critical reach is primarily a function of surface and subsurface crop and lawn irrigation return flows including administrative waste, ditch losses, on-farm losses and local precipitation runoff. The calculated local inflow after termination of irrigation tends to rebound to levels approximating 100 to 200 cfs of local inflow. Based on this data and considering the miscalculations of local inflow possibly caused by Grand Valley Project roller dam operations, precipitation, icing, gage inaccuracies, an uncalibrated rating curve at high flows, , .etc., we believe that the local tributary inflow to the 15 mile critical reach is on the order of 150 to 300 cfs. 6. On September 8-9 Piland and Associates measured 118 cfs of local inflows to the critical reach. 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. 7. Our estimated amount of local inflows during the periods monitored and extrapolation to an annual inflow are shown below. Also included for comparison is the annual inflow estimated from the Grand Valley Unit Salinity Control Project Hydrosalinity Studies conducted in the 1970's, Year Monitored Period Estimated Inflow Extrapolated during Period Annual Inflow 1991 August-November 52,000 156,000 1992 August-December 72,000 173,000 1993 August-December 57,000 137,000 1994 July-December 60,500 121,000 1976- Annual 114,000 114,000 Hydrosalinity Study Additional information or additional studies may significantly refine the annual inflow estimates.