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<br />....__A...__\.. <br />// .... ........ <br />.to...... t: "- <br />/ . ' <br />.y <br />/ " <br />/ "- <br />/ ~ <br />/ "- <br />/ " <br />... / " . <br />/ ,. <br />a/ ~. <br />/ . .. . ""'- <br />!a-.- - -t-- .- -j- ~ - ----&- - ------..------ - ---. --I-- - -... ~- . <br />. .. ~ <br />.. -4 <br /> <br />on any particular date for which dala are available <br />with no consideration for the carryover effect of <br />thermal mixing on previous or future dates. It is <br />now necessary to convert these parameter values to <br />some chronological time interval in order to <br />introduce the effect of various secondary phenom. <br />en on and to eventually determine the entire <br />seasonal or annual suppression. <br /> <br />The temporal unit used in subsequent portions <br />of the model is one month. The monthly values are <br />determined by plotting various point measure- <br />ments or computations versus time and then <br />interpolating to select the average monthly value. <br />This was done for point values of suppression. <br />surface temperature. bottom temperature. and <br />draw down. Figure 13 shows an example of these <br />relationships for a single reservoir. Lake Powell. <br /> <br />Program 5: <br />Heat Added Due to Decrea8ed Evaporadou <br /> <br />Evaporation causes a removal of heat from a <br />body of water equal to the latent heat of vaporiza- <br />tion which can be computed as follows (Paily et aI., <br />1974): <br /> <br />L = 597.31 - 0.561 T <br /> <br />........--.... :5 Y.or A....rOIl. Sl.Ippr..lion (ld.olized) <br />~ Surfoee Temperature <br />-a-....... Bottom Tlmperotur., <br /> <br />50 <br /> <br />z <br />o <br />~ 40 <br />'" <br />a: <br />.. <br />~ 30 <br />'" <br /> <br />0- <br />~ 20 <br />u <br />a: <br />'" <br />.. 10 <br /> <br />o <br /> <br />where L is the latenl heat in calories/gram and Tis <br />water temperature in oc. The May to October <br />surface temperatures in Utah are seldom less than <br />100 nor more than 250 suggesting a latent heat <br />range of 592 to 583 calories per gram. Since most <br />summer temperatures will average close to 200 a <br />value of 585 was used in the model. <br /> <br />The program computes the increase in mixed <br />reservoir temperature due to suppression as <br />follows: <br /> <br />TPLS = (585) VSUPP/VOL(I) <br /> <br />where TPLS is the increase in temperature, VSUPP <br />is the monthly volume of evaporation decrease in <br />acre feet and YOLO) is the total reservoir volume at <br />lhe average draw down for that month. The volume <br />ratio eliminates the need for a gram to acre foot <br />conversion factor. <br /> <br />The volume of suppression is computed as the <br />monthly idealized suppression factor multiplied by <br />the normal total monthly evaporation volume. The <br />volume of normal evaporation is estimated as <br />follows: <br /> <br />30 <br /> <br /> <br />25t <br />'" <br />a: <br />20~ <br />" <br />a: <br />'" <br />15 ~ <br />'" <br />0- <br /> <br />10 <br /> <br />5 <br /> <br />JAN <br /> <br />FEB MAR APR MAY JUN JUL <br /> <br />AUG SEP <br /> <br />OCT NOV 8~'~ <br /> <br />Figure 13. Temperatures and Idealized suppresolou rates ou Lake PoweU. <br /> <br />28 <br />