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Figure 3 shows the quantities of diversion water and return flow for each year of record, their salinity in milligrams per liter, and their salt content in tons. The bottom plot shows the net salt dis- charge in tons, which was tabulated above. From 1971 through 1975, there was a relatively consistent net discharge of salt in spite of variations in acre-feet and salinities. The average net discharge during those years was approximately 145,000 tons. The 1976 net salt discharge from the District was unusually high. As shown on the plots, it was accompani ed by a reduction in di ver- sions, and a slight increase in drainage. This situation is attri- buted mainly to the tropical storm of September 1976, which brought an unusually heavy summer rainfall (2.62 inches at Blythe gage) and interrupted i rri gat ion ope rat ions. At the same time return f1 ows continued without decrease, possibly because of rainfall runoff and a lag in discharge of subsurface drainage. Surface runoff from the piedmont areas to the west may have brought in a minor amount of salt, which discharged through the drains. Another tropical storm caused 1.46 inches of rain in August 1977, which may be the reason why the 1977 salt discharge did not drop back to the 1971 to 1975 range. The events of 1970 seem to have similar relationships to those of 1976; a rainfall of 1.82 inches occurred at Blythe in July 1970. The ISSP data are based on measured inflows and outflows. Not included are some inflows of water and salt that are not subject to measurement, particularly ground-water inflows from the piedmont areas on each side of the river. There may also be minor unmeasured surface inflows or outflows of water and salt from the District, all of which 1 eave potential for refi nement of the ISSP data. However, the data from the ISSP Program are regarded as good i ndi cators of the general magnitudes and trends of salinity in the river and the Oistrict. 002851 11