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Show Utah Geological and Mineralogical Survey, Water- Resources Bulletin 14, 1970 possible range in ground- water inflow to the north part is estimated to be from 10,000 to 40,000 acre- feet. Substituting the above ranges of values in the formulas results in an estimated range of possible net inflow to the north part during the 1969 water year of 670,000 to 1,240,000 acre- feet. Using the average of these two figures gives an estimated net inflow through the causeway to the north part of about 1 million acre- feet. As a check, the net inflow through the causeway to the north part was also estimated from data collected during the first 7 months of the water year ( October- April), when evaporation is minimal. From October 1968 through April 1969, the volume of the north part of the lake increased by about 700,000 acre- feet. During the same period, the discharge through the culverts ( and presumably through the fill as well) was about one- half the total discharge for the year. Thus the net inflow to the north part for the year was about twice the October- April inflow, or about 1,400,000 acre- feet. It is assumed that about 80 percent of the net inflow to the north part comes from discharge through the causeway, and the remaining 20 percent from surface runoff, ground- water inflow, and precipitation. Hence, the net inflow through the causeway for the water year is 80 percent of 1,400,000, or about 1,120,000 acre- feet. From the net inflow through the causeway to the north part during the year and the net northward discharge through the culverts, we can obtain the net northward discharge through the fill by difference: Acre- feet Net discharge through the causeway Net discharge through culverts Net discharge through fill 1,000,000 560,000 440,000 3. The total change in load in the south part of the lake for the 1969 water year was assumed to be entirely due to northward movement through the causeway. It was estimated from chemical analyses and volumes, thus: change in load = ( initial concentration x initial volume) - ( final concentration x final volume) = ( 355 tons/ ac- ft x 5,770,000 ac- ft) - ( 295 tons/ ac- ft x 6,220,000 ac- ft) change in load = 210 million tons loss. 4. The load movement in each direction is calculated from the relationship: VlC!- V0C0 = L ( A) where Vj = average discharge northward, V0 = average discharge southward, M = average concentration of water in the south part, C0 = average concentration of water in the north part, and L = net load movement Now, Cj = 275 tons per acre- foot, C0 = 470 tons per acre- foot, and, for the culverts, Vj = 615,000 acre- feet, V0 = 54,000 acre- feet. hence: VJCI - 615,000 x 275 = 169 million tons ( load moving northward) and: V0C0 = 54,000 x 470 = 25 million tons ( load moving southward) so: L ( culverts) = 144 million tons northward But the total net load movement was 210 million tons northward, so: L ( total) = 210 million tons and: L ( culverts = 144 million tons hence: L ( fill) = 66 million tons northward Now, for the fill, the values of Cj and C0 are unchanged; and, for the fill, L = 66 million tons, VI " vo = 440,000 acre- feet; so V0 = Vt - 440,000 hence, using relationship ( A) again, ( Vj x 275)- ( Vj - 440,000) x 470 = 66,000,000 and: Vj = 720,000 acre- feet but: V0 = Vj - 440,000 so: V0 = 280,000 acre- feet and: WYfW0 = 2.6/ 1 so, for the fill; hence: Vfy = 720,000 x 275 = 198 million tons ( load moving northward) V0C0= 280,000 x 470 = 132 million tons ( load moving southward) 39 |