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Development of Estimated Daily Flows - Yampa River at Maybell groundwater return flows (stream depletion on any given day is the net of diversions and return flows on that day). In order to estimate historical depletions due to irrigation, an EXCEL spreadsheet was created to calculate actual consumptive use and return flows to the Yampa River. This analysis was conducted for each of the eight land groupings identified. Input to this calculation included I) irrigated area; 2) historical diversions to those lands; 3) potential consumptive use; and 4) assumptions relating to ditch losses, application efficiencies, and return flow characteristics. Return flow characteristics reflected distance from the irrigated lands to the river and hydraulic conductivities of the underlying soils. These characteristics were used in a Glover analysis to determine monthly groundwater return flow lag factors. Input data on irrigated lands, diversions and potential consumptive use were determined as previously described. Values for ditch loss rates, application efficiencies and return flow characteristics were assumed based on engineering judgment. We believe these assumptions are generally consistent with the methods of irrigation in the Yampa River Basin and the location of irrigated lands (Table 2). Table 2 land Grouping Characteristics Used in Glover Analysis of Return Flows Group Irrigated Ditch Application Valley Hydraulic Specific Saturated Area loss Efficiency Width Conductivity Yield Thickness lac.) (%J (%1 (ft.) (ft./dl (ft.) I 21,500 10 45 4,000 400 0.2 20 2 14,100 10 45 4,000 300 0.2 20 3 500 10 45 2,000 200 0.2 20 4 8,000 10 45 2,000 300 0.2 20 5 6,600 10 45 4,000 200 0.2 20 6 2,200 10 45 2,000 200 0.2 20 7 5,600 10 45 3,000 200 0.2 20 8 10,200 10 45 2,000 175 0.2 20 The agricultural depletion analysis generated eight sets of nw~y depletion values. Generally speaking, depletions are positive (diversions are greatee,return flows in each month) during the months of April through July. During the remaining months of the year, depletions are generally negative (return flows are greater than diversions in each month). Monthly depletion volumes were then converted to daily values using a spline interpolation scheme. Each of the eight daily data sets were then routed downstream based on the average distance of each land grouping from the Maybell gage and the travel time estimates discussed below. Estimated monthly depletions generated through the analysis were then compared to similar estimates by Division 6 for the period 1976 to 1982. On average the comparison was quite close. However, the Division 6 estimates tended to show somewhat more variability from year to year. AgrkultlJral depletions estimated through this study averaged roughly 78.000 acre-feet per year and ranged from a high of over 97,000 acre-feet (1978) to a low of 46.500 6