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2.2.1 Inflows - In this water budget Huntley estimates inflows to the Closed Basin consist of <br />surface water inflows, ground water inflows, precipitation, and ditch imports. <br />Surface water inflows from the San Juan Mountains (70 kaf/yr) are based on the long-term <br />average gaged flows of Kerber, Saguache, Carnero, and La Garita Creeks. No other surface <br />water is estimated to occur from the other tributary San Juan mountain drainage basins. <br />Surface water inflows from the Sangre de Cristo Mountains (189 kaf/yr) include the gage <br />flows of N. Crestone Creek, and estimated gage flows for 10 other tributary basins with <br />intermittent streamflow records. The streamflow records for tributaries with intermittent <br />records were graphed against N. Crestone Creek records to derive a relationship to estimate <br />long-term average annual inflows to the Closed Basin. The relationships are shown <br />graphically but the statistical strength of the relationships was not provided in the report. <br />Four of the graphed relationships are based on only 5 data points. <br />Ground water inflows to the Closed Basin were estimated to equal outflows from the San <br />Juan (485 kaf/yr) and Sangre de Cristo (65 kaf/yr) mountain ranges using the water budget <br />equation o£ <br />Inflows (precip) -Stream Discharge - Et = Mtn. Ground Water Outflow <br />Precipitation inflow was estimated from the US Department of Commerce Normal <br />(1931- 1960) Isohyetal Maps for May-September, and October-April. Precipitation <br />was estimated by applying the mean basin precipitation times the basin area. <br />Stream discharges were estimated as described above. <br />Evapotranspiration (Et) for the mountains was estimated at 11.68 in/yr. This value <br />was derived by summing summer time Et (May to September) of 9.27 inches and <br />winter snow sublimation of 2.4 in/yr. The summer time Et is based on a rough <br />assumption that lake evaporation in the mountains is 4 in/yr less than lake <br />evaporation in the San Luis Valley, therefore potential Et (33.1 in/yr) in the <br />mountains is 4 inches less than potential Et in the Valley (37.4 in/yr). Actual Et <br />(9.27 in/yr) versus potential Et of forested areas is estimated from another study in <br />Colorado (Betters, 1975) to be 28 percent of potential Et. Betters (1975) simulated <br />forest runoff with errors on the order of 10 percent. During the winter (Oct-April) <br />Et is estimated at 2.4 in/yr to account for sublimation from snow based on average <br />results of three other studies located in Utah, Colorado and Nevada. The total <br />annual Et of 11.68 in/yr was applied to the basin areas. <br />Ground water outflow was then computed as the residual term. <br />Huntley also estimates a small amount of ground water inflow (8 kaf/yr) in the unconfined <br />aquifer as it enters the Closed Basin from the southern boundary where the ground water <br />divide is not well defined. <br />Precipitation inflow (765 kaf/yr) to the Closed Basin was also estimated from the US <br />Department of Commerce Normal (1931- 1960) Isohyetal Maps for May-September, and <br />October-May by applying the mean basin precipitation times the basin area. <br />Irrigation water imported to the Closed Basin from Rio Grande ditches was estimated from <br />PowelPs (1958) study of the San Luis Valley, where P.B. Mutz of the Bureau of <br />Reclamation completed aninflow-outflow study for the four-year period of 1949-1952. <br />During this period, imported water to the Closed Basin from ditches was estimated at 265 <br />rg_task8-1_2001-08.doc 7 of 19 Apri16, 2001 <br />