RGDSS_Task8-8_HistoricMonthlyModel_BaseflowCheckandSimulationRuns

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approach and aggregated classes as an aggregated diversion (aggregation is described in a memorandum documenting Task 8.1 of the Surface Water Model development. The capacity of a well structure is the sum of the individual well water right (permit) capacities associated with that structure. Well Return and Depletion Locations As with surface diversion structures, well pumping may result in depletions and/or return flows to a surface stream. The locations and timing of depletions and return flows are described by the Unit Response Functions developed by the Groundwater Contractor. The utility makertn was used to make specific assignments to nodes represented in the surface water model Makertn creates three different files which are used by the DMI watright in the creation of the direct flow station (*.dds) and well station (*.wes) files and describe the location of depletion and return flow impacts within the surface water model network. It should be noted that many of the URF assignments made in the surface water model result in return flows that are less than 100 percent of the unconsumed water. This occurs because portions of water applied to farms percolates into the groundwater aquifer, and is lost with respect the surface water system. Similarly, the deplete effects of pumping may not equal 100 percent of the pumping volume. This situation occurs when a portion the pumpage comes from groundwater storage, or salvage. Historic Groundwater Pumping Historic pumping by groundwater wells for agricultural purposes in the San Luis Valley was estimated by the Consumptive Use Contractor following a process described in the documentation for the State's Consumptive Use Model (StateCU). For all but two modeled diversion structures, historic pumping was estimated by examining the calculated potential consumptive use, historic surface water diversions, conveyance and application losses, and soil moisture conditions. Potential consumptive use not met from surface water supplies and soil moisture was estimated to be supplied from groundwater. Required pumping volumes were then adjusted to reflect application efficiencies. Municipal Well Use Municipal water use was also added to the surface water model during Phase lc model development. There are numerous incorporated towns and cities within the San Luis Valley that provide raw or treated water to their residents for domestic, municipal and industrial purposes. These are predominantly supplied from groundwater pumping systems. Domestic water use outside of city service areas (unincorporated areas) is most commonly supplied by small private groundwater wells. Table 1 illustrates recent populations for 15 of the largest cities and towns in the San Luis Valley as estimated by the Colorado Department of Local Affairs (CDLA). Excluded from the Table are the smaller towns, and unincorporated areas. The total 1997 population of the San Luis Valley, including cities, rural and unincorporated areas has been estimated by the State of Colorado at approximately 45,000 (CDLA). The municipalities shown in Table 1, therefore, represent about one-half of the total Valley population. The populations used to estimate water uses shown in Table 1 have been adjusted to reflect that cities and towns typically provide water service to people living outside of their incorporated city or town limits: reported municipal populations C:Acdss\Task8-8.doc Phase lc Model September 27, 2000 -Page 3 of 17