Laserfiche WebLink
Section 5 <br />Projected Water Use <br />value is suitable as a basinwide average, variability from <br />one area or city to the next can be expected as a <br />function of the relative mix of water uses, land use <br />density, vegetation, elevation, and climate. <br />subbasins. Figure 5-4 shows the water districts <br />throughout the state and this section will refer to water <br />districts for those basins where DSS analyses have been <br />completed. <br />Based on this previous work, SWSI determined that an <br />average M&I CU factor of 35 percent was an appropriate <br />reconnaissance level value for calculating the M&I water <br />demand for each county, and for each scenario. This <br />statewide average CU factor for M&I use is assumed <br />representative of the range of municipal CU that varies <br />by microclimate, development densities, and <br />residential/commercial/ industrial mix throughout most of <br />the state. Routt and Moffat Counties in the Yampa/White/ <br />Green Basin are exceptions due to the presence of high <br />CU thermal-electric power plants that represent a <br />significant percentage of total M&I and SSI water use. <br />5.1.2 Method for Estimating Agricultural <br />Use <br />Colorado's DSS was used to estimate existing <br />agricultural water demands in the Colorado, Gunnison, <br />Rio Grande, Dolores/San Juan/San Miguel, and the <br />Yampa/White/Green Basins. DSS modeling tools are <br />described further below. Agricultural use in the Arkansas, <br />North Platte, and South Platte Basins was estimated <br />using a variety of available sources as described below. <br />Future (2030) agricultural water requirements were <br />estimated using existing requirements and projected <br />future irrigated acreage. In other words, the requirement <br />per irrigated acre is assumed to remain constant and <br />future changes in water requirements are assumed to be <br />linearly related to the projected changes in irrigated <br />acreage. Projected irrigated acreage values represent a <br />range based on feedback from Basin Roundtables and <br />Basin Advisors, an analysis of M&I water acquisition <br />practices, and land development trends in each basin <br />using GIS coverages of irrigated acres, where available. <br />It is usually more meaningful to describe agricultural <br />demands within a basin at the water district rather than <br />county level, since water districts generally follow <br />~ <br />$~ole'ri~ice Wo~e' $upplY Initia~ive <br />5.1.2.1 Existing Demands Method: <br />DSS Basins <br />For the Colorado, Gunnison, Yampa/White/Green, <br />Dolores/San Juan/ San Miguel, and Rio Grande Basins, <br />DSS data sets (specifically for StateCU) were used to <br />quantify the existing conditions. Projections of future <br />agricultural use were made based on existing irrigation <br />practices and water availability conditions, and projected <br />changes in irrigated acreage. <br />Input data sets include tabulated irrigated acreage and <br />crop types associated with each agricultural diversion <br />structure in the river basin, as well as historical regional <br />weather conditions. Monthly crop irrigation water <br />requirements (IWR) are generated in the model for each <br />diversion structure using these data and the modified <br />Blaney Criddle equation. <br />IWR values represent the maximum volume of irrigation <br />water, after effective precipitation is taken into account, <br />which would be consumed to grow particular crops. <br />Effective precipitation is the portion of the total <br />precipitation (after surface evaporation plus runoff, deep <br />percolation, etc.) that is stored in the soil and is available <br />to the crops. IWR values do not include farm application <br />losses and conveyance (e.g., ditch) losses. If the IWR <br />can be met with available water supplies, the crops will <br />provide a full yield; otherwise, the crops are "water <br />short." The amount of water that must actually be <br />diverted at the river (or pumped from wells) to meet the <br />crop requirements at the farm will typically exceed the <br />IWR. This is due to canal or other delivery system <br />losses, and the fact that not all of the water delivered to <br />the farm or ranch can be used with 100 percent <br />efficiency. In StateCU, river diversions are assumed <br />equal to the input set of known historical diversions at <br />each structure. <br />~~ <br />S:\REPORT\WORD PROCESSING\REPORT\SS 11-7-04.DOC ~J-7 <br />