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<br />Section 5 <br />Consumptive Water Needs in the South Platte Basin and <br />Denver/South Metro Counties <br /> <br />IIIII <br /> <br />Five studies of estimated conservation savings that <br />followed similar methodologies for estimating <br />conservation savings were reviewed in estimating <br />Level 1 conservation savings for SWSI. The average <br />expected percent reduction in baseline water demand <br />from Level 1 conservation savings based on these <br />studies were identified as shown in Table 5-3. <br /> <br />Table 5-3 Anticipated Level 1 Conservation Savings by Year <br />III "~lill___~Ii'~I_ I I <br />Expected Savings 2.5% 5.0% 7.0% 8.5% <br />Increase above 0% 2.5% 4.5% 6.0% <br />2000 <br /> <br />Year <br /> <br />Year 2000 water use data were used to develop the <br />SWSI baseline demand forecast. Thus, the SWSI <br />baseline demand forecast is reflective of water <br />conservation (both passive and active) in effect in the <br />year 2000. Conservation adjustments to the SWSI <br />baseline demand forecast should reflect future impacts of <br />conservation. <br /> <br />The M&I baseline water demand for each county was <br />adjusted by these percent savings factors to account for <br />the impact of Level 1 conservation savings. The resulting <br />estimate is used as the lowest conservation scenario <br />(Level 1 ). <br /> <br />5.1.1.6 Estimate of M&I CU Rates <br /> <br />Water use can be considered both in terms of gross <br />water needs - the total amount of water delivered to a <br />user - and in CU. Both are important considerations in <br />water planning. The difference between gross and CU is <br />the amount that is realized as return flows (i.e., through <br />wastewater treatment plants and lawn watering). CU is <br />generally higher in arid and semi-arid regions such as <br />Colorado, where more water is used for irrigation and <br />lost to evapotranspiration. <br /> <br />5.1.1.7 Existi ng Agricultural Demands Method <br /> <br />The South Platte Basin does not have Decision Support <br />System (DSS) data sets. Hence agricultural demands <br />were estimated using preliminary estimates of irrigation <br />water requirements (IWR) and irrigated acres developed <br />during preliminary work on the South Platte DSS. <br />Projections of future agricultural use were made based <br />on existing irrigation practices and water availability <br />conditions, and projected changes in irrigated acreage. <br /> <br />CONI <br /> <br />5-6 <br /> <br />Summaries of the agricultural demand sources for the <br />entire South Platte Basin is included in Table 5-4. <br /> <br /> <br />5.1.1.8 Future Agricultural Demands Method <br /> <br />Future (2030) agricultural water requirements were <br />estimated by basin using annual average requirements <br />on a per acre basis, and projected future irrigated <br />acreage. The current requirements (AFY) are normalized <br />to the current irrigated acreages (acre-feet per acre per <br />year [AF/Ac/Yr]) and multiplied by the projected 2030 <br />acreages to arrive at a future total agricultural <br />requirement (AFY). In other words, <br /> <br />2030 Ag Irrigation Water Requirement (AFY) = <br />Current Average IWR Requirement (AF/Ac/Yr) x <br />Projected Irrigated lands (Ac) (5.1) <br /> <br />where <br /> <br />Current Average Requirement (AF/Ac/Yr) = <br />IWR/Current Irrigated lands (5.2) <br /> <br />2030 water supply limited (WSL) CU; incidental losses, <br />livestock watering, and stock pond evaporation; and <br />gross diversions were estimated using the same <br />approach (Equations 5.1 and 5.2). Projected WSL values <br />represent anticipated crop CU, assuming the ratio of <br />available supply to irrigated acreage stays the same. <br />Incidental losses, livestock watering, and stock pond <br />evaporation represent additional water consumption <br />associated with the projected irrigated acres. Gross <br />diversions reflect the anticipated amount of water <br />actually diverted at the stream to provide this level of <br />combined CU. Basin average annual diversions <br />(averaged over the period of record) were used in <br />Equation 5.1 for these calculations. Results are <br />presented and discussed in Section 5.3. <br /> <br />Projecting future agricultural water demands includes an <br />evaluation of potential changes in irrigated acres, as well <br />as an estimate of agricultural water use per acre. <br /> <br />S:\1177\Basin Reports\South Platte\S5_South Platte.doc <br />