WSP09197 - Laserfiche WebLink

Home Browse Search

. ...... ~ ~ O::l \. . SPECIAL STUDIES (continued) Present Study For the purpose of this study, 14 estimates of the 1979-2010 condi- tions were made by running 14 passes through the CRSS. The initial pass was made starting with 1906 hydrology in 1978 and running for 32 years; the starting year was then incremented by 5 years, such that the 1979-2010 period used the 1911 to 1942 hydrology. In this way, incrementing the natural flow data base 5 years each time, 14 estimates of the 1979 to 2010 conditions were developed. This allows the extremes as well as the means to be displayed and considered. This whole process was done twice, once without any Water Quality Improvement Projects in place and once with all of the Water Quality Improvement Projects coming on line according to the present schedule. Table F contains the mean flow and flow weighted mean salinity at 21 stations throughout the basin for years 1990, 2000, and 2010. It should be noted again that these estimates differ from those presented in table D for three main reasons: A. The CRSS uses the 1906-1974 period of record, rather than 1941-1978, resulting in an average 1 million acre-feet more water available per year. B. The reservoir levels are allowed to rise and fall over their entire permissible range, resulting in different evaporation rates, and greater water availability during low flow years. C. The effects of development in the Upper Basin are buffered as the river passes through Lakes Powell and Mead, resulting in a lag of 3 to 5 years before the impacts are perceived at Imperial Dam. Table G contains the same parameters as Table F but with the effects of the salinity control projects considered. Figures 9 and 10 represent the range of salinities that may be antici- pated at Imperial Dam, without and with the effects of the Water Quality Improvement Projects. For the CRSS, four curves are presented: 1. Probable minimum 2. Mean 3. Most probable 4. Probable maximum The probable minimum represents the average of the three lowest salinities out of the 14 passes conducted for each year; the mean is the flow weighted mean salinity of the 14 passes; the most probable curve was computed as the mode or the salinity that was exceeded 50 percent of the time; and the probable maximum is the average of the highest three out of 14 salinities for" each year at Imperial Dam. For comparative purposes, figure 9 also contains the table D estimates. Figure 10 displays the schedule of Water Quality Improvement Project salt load reduction. 111