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Development of Estimated Daily Flows - Yampa River at Maybell Daily Virgin Flows at Maybell Estimated daily virgin flows at Maybell were calculated according to the following general formula: . Daily virgin flow equals: daily gaged flow, plus routed daily depletions at Steamboat Springs, Hayden and Craig, plus rputed daily diversions at the Craig and Hayden Stations, plus routed daily depletions for each of the eight irrigated lands groupings. plus routed daily diversions for transbasin export, plus routed daily reservoir depletions, plus daily diversions at the Maybell Canal. Adjustments to Virgin Flows Estimated daily virgin flow at Maybell over the 33 year study period were examined to check for the presence of negative values in the calculation results. Negative virgin flows, while not possible from a physical standpoint, can result due to the adjustment applied for agricultural depletions. As previously described, depletions from irrigation are typically negative during all but a few months as groundwater flow returns to the river in a lagged fashion. Adjustment for a negative historical depletion results in a virgin flow that is less than gage flows (Le. the return flow would not have happened without irrigation activity). The review of estimated virgin flows revealed several days with negative calculated values generally ranging from -10 cfs to -20 cfs. The fact that these values exclusively occurred during the months of September and October suggested that estimates of return flow characteristics could be improved. In an attempt to eliminate these occurrences, assumptions on hydraulic conductivity were modified in the calculation of agricultural depletions and new virgin flows estimated (final return flow parameters are shown in Table 2). Although these changes reduced the number of occurrences, negative values still resulted in approximately 50 days of the roughly 12,000 daily flow calculations. Rather than further modifying assumed return flow characteristics, these negative values were set equal to 10 cfs. Given the large drainage area above the Maybell gage and the geology of the area in the vicinity of the gage, we believe it unlikely that flow levels would drop below this level under virgin conditions. DAILY MAYBELL FLOWS: FUTURE CONDITIONS WITHOUT-PROJECT Estimated daily flows at Maybell reflecting future (year 2040) without-project conditions were developed by subtracting estimated daily depletions associated with year 2040 water uses from the estimated daily virgin flows. Year 2040 water uses were generally those defined and used in the Phase I and Phase 2 studies. Future daily depletion estimates were developed, in general. by factoring the daily depletion estimates developed in estimating virgin flows to year 2040 use levels, "backcasting" them over the entire study period, and subtracting them from the virgin flow estimates. 10