LESS

Abstract

Since about 1950 the inflow of the San Joaquin River to the Delta has been, and still is being greatly reduced. There are long periods when there is no net outflow from the river to the Central -Delta (WRINT-SDWA 19). This causes stagnant water reaches with loss of salinity control and inadequate dissolved oxygen for fish. Upstream appropriative rights granted by the State Board often exceed the total yield of the river system, and direct diversion rights are based on diversion amounts rather than on consumptive use. Appropriators, therefore, are able to keep increasing their consumptive use of the water they divert with a consequent reduction in return flows. Exports from the Tuolumne River to the Bay Area bypass the stream system and have increased about five fold over the last forty years. SDWA 121 shows the effects of some of these diversions on the Delta in a dry year such as 1977. Appropriators on the tributaries with junior water rights have not been required to bypass sufficient unimpaired flows to protect senior water rights and natural channel depletions in the San Joaquin River and southern Delta. The net effect of CVP operations alone is to reduce river flow upstream of Vernalis by about 130,000 acre feet in dry years and 560,000 acre feet in below normal years. This is discussed in the June 1980 joint report by USBR and SDWA on "The Effects of the CVP Upon The Southern Delta Water Supply". That report was submitted in Phase I of the Delta Hearings as SDWA 4 and a graph depicting those effects is at SDWA 26.