| OCR Text |
Show 61 first kept, has varied from a high of 4211.5 feet in 1873 to a low of 4191.6 feet in 1963. The historical hydrograph in Figure 8 indicates a marked decreasing trend in the elevation of the Lake. Although it is not yet possible to predict future fluctuations of the Great Salt Lake, the analysis of past data can indicate some possible expectations. The hydro- graph shown in Figure 9, which was developed by Professor Joel Fletcher at Utah State University, shows yield from 1280 to present within the Great Salt Lake Basin by correlating the growth rate in tree rings with available historical data in the Basin. To indicate the relationship between the historical stage hydrograph and the 1280- to- present yield hydrograph in the Basin, the hydrograph in Figure 8 is superimposed on Figure 9 from 1901 to 1973. This superimposi- tion suggests that the present declining trend shown in Figure 8 is only a declining portion of a cycle of rising and declining trends and should be expected to reverse itself in the future. Another method of estimating future Lake levels and volume is through an analysis of the probabilities associated with past Lake elevations and conditions. Figure 10 shows probability curves for 1901- 1973 for several kinds of estimates: ( 1) natural or historical elevation, based on records of past elevations; ( 2) historical elevation, adjusted as if there were no man- caused reduction of inflow; ( 3) present modified elevations, those which would have occurred under 1901- 1973 climate conditions with the present level of consumptive use; and ( 4) future modified inflow, showing effect of future developments as if existent over the period of study. ( Due to the uncertainty of future developments, this estimation is projected for one, two, three, four, five and six hundred |
