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<br />nG~~2S <br /> <br />In terms of electric energy this is 19.3 (10') <br />Kilowatt-hours (KWH) required annually. <br /> <br />If the 140,000 acre feet of water salvaged <br />annually by thermal mixing is used to generate <br />hydro power as it leaves the reservoir. it would add <br />the following to the annual generating capacity of <br />Glen Canyon Dam (ignoring the portion of this <br />additional capacity also added to the Hoover Dam <br />generators). <br /> <br />Assuming an average resenroir draw down of <br />80 feet, the average head on the Glen Canyon Dam <br />turbines is 484 feet. The combined turbine and <br />generator efficiency is 0.905 <USBR, 1970). The <br />generators should therefore produce 447.4 KWH of <br />power per acre foot ofwaler or 63.S (IO') KWH per <br />year for the salvaged water. This suggests that 3.3 <br />times as much power would be generated from the <br />salvaged water as it took to "create" the water. The <br />power revenue profit from this operation would of <br />course depend upon whether wholesale or retail <br />cosls are used in the analysis. If $0.01 per KWH is <br />selected as value of electrical power. the potential <br />annual profit from hydro power generation of Glen <br />Canyon Dam alone would be $442,000. <br /> <br />After generating hydro power, the salvaged <br />water would still be available for other uses such as <br />cooling of fossil fuel fired generators. Using 15 acre <br />feel of water per megawatt (MW) of power <br />capacity as the cooling requirement (Western <br />States Water Council, 1974) 142,000 acre feet of <br />additional water could provide the cooling for <br />9,500 MW of generating capacity. A similar <br />analysis could be made for impact of Flaming <br />Gorge hydro power generating capacity. <br /> <br />Another aspect of the potential benefits on <br />Colorado River impoundments is related to salinity <br />problems in the lower basin. The damages to <br />agricultural production in the lower basin due to <br />increased salinity in the river has been estimated by <br />the USBR at $230.000/ppm. Evaporation suppres- <br />sion in effect adds water with zero salinity to the <br />reservoir. On Lake Powell for example the ratio of <br />waler salvaged to average reservoir storage (I6 mat) <br />is 0.9 percent. The TDS of Lake Powell at <br />Wahweap is 600 to 700 ppm (USBR unpublished <br />Lake Powell Quality Data). An addition of 0.9 per- <br />cent of pure water annually should lower the TDS <br />of the Lake by 6 ppm. Since now through Lake <br />Powell represents almost the entire flow to the <br />lower basin this represents a dilution benefit of <br />11.380.000 10 irrigated agriculture for quality <br />improvement in addition to the value of the <br />ultimate use of the salvaged water. <br /> <br />Increased eyaporallon below <br />Impoundments <br /> <br />Since the annual net suppression is closely <br />related to the removal of excess heat from the <br />reservoir an important question in applying the <br />model to some reservoirs is how much of this <br />claimed net benefit is ultimately lost by the <br />resulting increased evaporation in the river. canal. <br />or other downstream reservoirs. <br /> <br />On most Utah impoundments the reservoir <br />outflow after high spring runoff is transported <br />almost entirely in either pipelines or canals to the <br />point of use. The travel time to the point of use is <br />relatively short so that additional evaporation from <br />canals is negligible. <br /> <br />For the major Colorado River impoundments <br />(Lake Powell and Flaming Gorge) the increase in <br />river losses appears also to be minor. For example, <br />now from Lake Powelltra,'els through 295 miles of <br />narrow river before entering Lake Mead. The travel <br />lime is less than 3 days and the additional <br />evaporation in the river due to the added heat is <br />eSlimated at 3 104 percent of the annual volume of <br />water salvaged. <br /> <br />This quantity was estimated as follows: The <br />average increase in outflow temperature due to <br />mixing (TMIXC-TBOT) from Appendix H is <br />7.90C. Figure 12 indicates that this would produce <br />a 40 percent increase in river evaporation; however, <br />this assumes that all of the additional heat which is <br />removed from the river is accomplished by <br />evaporation only. Actually, in the turbulent river, <br />heat transfer by conduction would become <br />significant. both from the air and the wetted <br />perimeter. The air above the river will normally be <br />substantially warmer than the reservoir outflow <br />water (either normal or destratified) and therefore, <br />heat is transferred into water rather than from it. <br />Destratitied outnow will decrease this gradient and <br />therefore slow this heat transfer process. It is not <br />clear what the range of evaporation rates from the <br />river may be. The cold water surface interfaces a <br />very warm air mass which is mostly shielded from <br />the wind and therefore may have quite a high vapor <br />pressure. This condition could cause the vapor <br />pressure deficit (and therefore the evaporation) to <br />approach zero. However because of the turbulence <br />oflhe surface the USBR estimates the annual river <br />evaporation at 6 feet. This indicates that about <br />17.000 acre feet of annual evaporation normally <br />occurs on this reach of the river. Using .JO percent <br />as a more probable estimate of river evaporation <br />increase. the evaporation on the river above Lake <br />Mead due to mixing would be 5.100 acre feet which <br />is 3.6 percent of the estimated volume saved on <br />Lake Powell. <br /> <br />47 <br />