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Show 24 Utah Geological and Mineral Survey Water- Resources Bulletin 21, 1976 by the budget equation ( 1) Letting AS, as computed by the model, be ( AS) m and that of the observed lake altitudes be ( AS) o, the net deficit can be represented by lum = ( AS) o - ( AS) m. The deficits in net inflow ( total inflow less evaporation) indicated by the second model computation cannot be precisely attributed to any parameters in the water- budget equation. The deficits, however, generally became larger during periods of falling stages and smaller during periods of rising lake stages. The deficit ( lum) was tested as a function of the observed lake altitude, SI, or lum = ( SI - 4190) c, where 4190 is the lake altitude at which the deficit ( lum) was approximately zero and c was a constant representing the slope of the relationship between ( SI - 4190) and lum. The value of c was determined by repeated runs of the model and selection of the best fit between the observed and computed lake altitudes. All unmeasured inflows plus errors in the estimate of the other parameters can be incorporated into the factor lum. The computed monthly values of lum were then added to the inflow estimates for the base period and the budget equation for the 1931- 73 base period became: AS = Is + Ig + Ip + lum - Oe ( 3) Figure 9 shows that in the third model computation using the net inflows as computed by equation ( 3), the computed lake altitudes converge near the observed altitudes. The annual inflow to Great Salt Lake from the three major tributaries and other parameters within the budget equation is shown in figure 10. The total annual inflow ( Is + Ip + Ig + lum) during 1931- 73 ranged from about 1.5 to 5 million acre- ft ( 1,849.5 to 6,165.0 hm3). The Bear River contributes the largest percentage of the measured surface inflow. DIKING OPTIONS The options provided in the model for diking include combinations of eight areas east of a line joining Antelope Island, Fremont Island, and the Promontory Mountains, and the part of Great Salt Lake that lies north of the Southern Pacific Transportation Co. causeway ( fig. 3). The dikes would extend from the Promontory Mountains to Fremont Island and from Fremont Island to Little Mountain. Except for the Southern Pacific Transportation Co. causeway, all dikes are assumed to have only one outlet to the south part of Great Salt Lake, with the width of the outlets being optional. The outflow is considered to be a function of the positive head difference from the diked part to the south part. The dikes are assumed to be impervious to seepage, and the outlet structures are to be operated to prevent density flows from entering the diked part from the south part. Areas evaluated for diking Diking Area option ( from fig. 3) 1 1 3 1+ 2 4 4 5 5 6 4+ 2 7 7 12 4+ 8 14 4+ 2+ 8 20 1+ 2+ 4+ 5+ 8 Only one diking option can be simulated during each run of the model. Once a diking option is chosen, the remainder of the areas are included with the south part. The Southern Pacific Transportation Co. causeway can be treated in two ways by the model. It can be treated as an impervious dike, similar to the other dikes with an outlet providing for flows from the south to north parts. Or it can be treated as a permeable structure with culverts as they now exist or with modified culvert widths as discussed by Waddell and Bolke ( 1973). SALT BALANCE The total load of salt in the north and south parts of Great Salt Lake consists of the dissolved load and the undissolved load. The annual inflow load to the lake is small compared to the total load in the lake. Thus, the inflowing load can be ignored in computations of the salt balance for the north and south parts. For any diked area being considered, however, it is necessary to know the inflowing load in order to compute the concentrations within the diked area. The salt balance for the Great Salt Lake with a diking option is depicted in figure 11. The dissolved load in the diked area ( LD) is dependent upon the selected diking option ( D), the time step within the base period ( t), and the outflow from the diked area ( OD). The dissolved load ( LD) contributed by the Bear, Weber, and Jordan Rivers was developed as a function of stream discharge. These relationships were developed at site 10126000 on the Bear River, site 10141000 on |