WSP07026 - Laserfiche WebLink

Home Browse Search

w 00 00 ~"7) CRSS COMPUTER SIMULATIONS Current Conditions Historical flow and salinity conditions for the Colorado River at Imperial Dam are depicted on figures 3 and 4, respectively. Figure 3 shows that the amount of water that reached Imperial Dam in 1983 was almost 17 million acre-feet. However, since the closure of Glen Canyon Dam, with the exception of 1980 and 1983, flows at Imperial Dam have fluctuated within the narrow range of 5 to 7 million acre-feet, primarily due to the filling of Lake Powell (1963-1980). The additional water in 1980 and 1983 had a diluting effect on the salinity concentrations at Imperial Dam and other upstream reservoirs. Figure 4 shows that the :flow-weighted average annual salinity in 1983 at Imperial Dam was 732 mg/L, the lowest level since 19.53 when it was 690 mg/L. In 1983 at Lake Powell, it is estimated that the sal inity levels were about 400 mg/L, down from about 525 mg/L in the previous year. The 1983 salinity reductions at Imperial Dam were due to excess flow and are expected to have only a temporary impact on future, salinity projections. Salinity reductions in Lake Powell will have an impact on short-term salinity projections, but will have no impact on long-term projections. The 1983 flow and salinity conditions represent the initial, or starting, conditionS for future CRSS scenarios. Significantly lower TDS at Imperial Dam, full reservoir conditions, and improved salt loading estimates, coupled with lower rate of depletions, have essent'ially slowed the projected TDS increase at Imperial Dam. Continued high flow conditions in 1984 are expected to further influence the conditions projected by the model. In addition, some entities had felt that the present level salt loading used by Reclamation in CRSS was too high. This sparked a number of studies to determi neif there we re trends in the hi stori ca 1 data base, 0 r if some errors had been made in the process of developing a natural flow and salt data base. Some trends were found in the historical salt load; however, the major part of the difference was in the natural salt load. Extrapolating salt-flow coefficients from a mean annual load to an annual load necessitated further adjustments due to the skew of the hydrologic data base. JhE!~e ~pjustments had the effect of reducing the natural salt load by approx'iiriiile.1'/400,OOO tons. This correction brings Reclamation's calculation of the natural salt load of the Colorado River closer to the Forum's analysis. Scenarios and Assumptions A total of ;five different scenarios were Evaluated using CRSS, with different combinations of Water Quality Improvement Projects and depletion schedules. . Appendix E contains the tables showing the tons of salt removed by the various units in the scenarios analY2ed by CRSS. Two different 23 ,j --~ -, J ';i /1 'j 1 j .:, ',-