OCR Text |
Show function of total system demand. Figure 5.18 shows the yield by reservoir as a function of total system yield, and Figure 5.19 shows the storage capacity by reservoir as a function of total system yield. Analysis of the optimal solutions from these parametric applications indicates that 80,000 acre- feet per year is perhaps a viable economic limit for the total yield from the 7 potential and 1 existing ( Mountain Dell) reservoir sites. This conclusion is prompted by the observation that the rate of increase of unit cost of treated water increases rapidly beyond this point. The most preferred reservoir sites appear to be on Big and Little Cottonwood Creeks. This is not surprising, since these are the streams with the largest average annual flow, and have competitive costs. As the demand level is increased, the optimal solution appears to be to increase the yields ( and hence storage) from Big and Little Cottonwood creeks. The Little Dell site ( currently under construction) does not appear to be economically attractive. For values of total system demand less than 100,000 acre-feet/ year, the largest capacity at Little Dell is 60 Acre- feet, and the yield 325 Acre- feet/ year. This yield is developed without a reduction of the Mountain Dell yield. The model prefers to sustain the yield at Mountain Dell, rather than increase the yield at Little Dell at the expense of the yield at Mountain Dell. This situation changes only after the annual system demand exceeds 100,000 acre- feet/ year. Prior to this transition, the reservoir sites at City, Red Butte, Emigration and Mill creeks enter the solution, and unregulated streamflows are treated at the sites. A recommendation to develop the Big and Little Cottonwood sites on an economic basis is thus made. 30000T City Creek Annual Flows Figure 5.9 Annual Inflows - City Creek site 141 |