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V. Description of Data and Software: South Platte Consumptive Use Model (SPCU) 2.0 South Platte Consumptive Use Model (SPCU) Water managers in the South Platte River Basin need an efficient process for accurately computing field and farm Consumptive Use (CU) to determine augmentation requirements for groundwater wells or estimate the amount of water available for a different use. Based on surface water supplies and consumptive use estimates, managers can estimate the CU of ground or surface water supplies using the SPCU Model. 2.1 Back!!round and ComDatibility with Other Systems Input for the SPCU Model can be developed through GIS themes and the spatial analysis features of SPGIS or entered directly into the interface. The SPCU Model computes CU monthly using the Blaney-Criddle or Kimberly- Penman methods for computing CU. The Kimberly-Penman method, as implemented in this model, uses monthly reference crop Evapotranspiration (ETr) estimates provided by NCWCD as part of their weather data. The Blaney-Criddle method is a monthly calculation based on temperature. The SPCU Model can also calculate daily consumptive use using the Penman-Monteith method. The SPCU Model computes CU by applying crop coefficients that describe water use characteristics of crops during the growing season, water supplies, and weather data. 2.2 Overview of Consumotive Use Calculation Consumptive use is primarily evapotranspiration (ET), which is water evaporated or transpired from plant foliage and adjacent soil during crop growth. The model assumes that water not consumptively used by crops returns to the river system via surface runoff or deep percolation. Three techniques have been selected based on the data availability in the South Platte River Basin (i.e., Blaney-Criddle, Kimberly-Penman, and Penman-Monteith). The Blaney-Criddle and Kimberly-Penman methods allow monthly calculations and the Penman-Monteith method can be used on a daily time step. The computation of potential ET for the Blaney- Criddle and the Kimberly-Penman methods includes an option for calculating a soil moisture budget. The Kimberly-Penman uses monthly potential ET estimates from a file and applies crop and area information to determine CU. For both of the monthly models, surface water supplies can be specified to meet crop CU. If there is additional CU beyond what surface water supplies can meet, wells tied to the farm are typically assumed to supply the additional CU, depending on the options selected. Weights can be assigned to weather stations, reflecting their relative influence. CU Model input datasets can be created using the Geographical Information System (SPGIS) capabilities in SPMAP. This process includes specifying modeling area and model information using ArcView from the spatial data populated in SPGIS. SPCU Model input data includes crop types, areas occupied by individual crops, planting dates, irrigation amounts, precipitation, soil types, and temperatures. Additionally, weather and water supply data can be added from State of Colorado HYDROBASE data files that can be retrieved from the internet. 2.3 Develooment of Graohical User Interface for Windows 95/98/NT/2000 The original CU Model was developed for the Colorado River Decision Support System, and is the basis for the Colorado Decision Support Systems CU Model being implemented in river basins throughout the State of Colorado. Completion Report: South Platte Mapping and Analysis Program 17