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<br />2370 <br /> <br />tend to reach the same salinity as the agricultural drainage and the <br />project would approach salt balance, except for remaining natural <br />vegetation. <br />The salt discharge caused by initial leaching of new lands would <br />continue as new lands are developed for irrigation. The discharge <br />during this future period includes a continuing discharge from the <br />land first irrigated between 1965 to 1976. The fluctuations on <br />Figure 5, Plot C, between 1977 and 1982 reflect fluctuations in the <br />yearly acreages to be developed. <br />The net effect plot of future conditions indicates that the pres- <br />ent trend of salt retention will continue for the next few decades. <br />The plot should be viewed as an approximation of future conditions, <br />recognizing the limitations of the data base and various possibilities <br />for future development other than as projected. <br />Other conditions of future development are possible, and might <br />change the salt balance significantly. For example, if the remaining <br />irrigable land were developed suddenly, the plot of salt balance would <br />rise temporarily and may rise above the zero line for several years. <br />Also, if more land than the 93,046 acres is irrigated and water use <br />efficiency is increased accordingly, the net salt discharge would <br />decrease. <br />It may be of interest that since 1965 the Reservation has <br />retained an estimated 1,400,000 tons of salt. This may be compared <br />to an estimated 12,700,000 tons contained in the ground water to a <br />depth of about 130 feet in 1965. Some of this incremental salt will be <br />flushed out very gradually in the near future, but most of it is <br />expected to be absorbed into the system, so to speak, since the <br />salinity of agricultural drainage will soon exceed the average ground- <br />water salinity. Some will also be accumulated under natural <br />vegetation. <br />It is not known how long natural vegetation might continue to <br />thrive on the flood plain and continue to cause salt storage. U . S. <br />Geological Survey experiments with salt cedar grown in large tanks <br />indicate that consumptive use of water by mature plants decreases as <br />the salinity of the root zone increases, declining to approximately <br /> <br />21 <br />