85 



high title liiit now to a large extent reclaimed, King prineip.ilK- along its northern 

 shore. The xolunietric contents of Siiisiui Ba\- are about 480, ()()() acre feet at Um- 

 tide and about 700, OOO acre feet at high tide, and the volumetric contents of San 

 Pablo Bay are about 1,000,000 acre feet at low tide and nearly 1,500, 000 acre feet 

 at high tide. These \-ohuiies of water are pushed back and forth by the tides, becoming 

 more salty during the protracted annual low water stage of the rivers and freshening 

 again to a greater or less degree as the rivers rise to their winter and spring high 

 stages. 



For a tidal range of 6 feet at the upper end of Suisun Bay, when the rivers are at 

 their low stages, that is, generally from some time in July to November, the volume of 

 water which is required to fill the tidal prism in the lower reaches of the Sacramento and 

 San Joaciuin Rivers may be noted approximately at 57,000 acre feet for the San Joaquin 

 River and 25,000 acre feet for the Sacramento Ri\-er. The discharge of the ri\ers, 

 when material, during the time inler\al bi'twt'en the extremes of tide, must, howe\'er, 

 be given consideration if a comparison is to Ije made l)etween the volume of flood flow 

 from the ba\- which is required to fill this tidal prism and the volume of water de- 

 li\ered into the liay from the ri\ers on the elib flow. The river discharge decreases the 

 volume of water moving up-stream on the flood tide and increases the volume of water 

 moving down-stream on the ebb tide. Variations in the \'ohnne of river discharge 

 are therefore reflected in\erseh' in the salinity of water in areas subject to lioth 

 influences. 



In seasons of substantially normal weather the discharge of the ri\ers into the 

 bay increases in September or October from its low summer stage, irom \'arious 

 causes: there is then a decrease in the e\'aporatioii Irom the water surface of the 

 rivers and delta channels, there is a decrease in the irrigati(jn draft, and the winter 

 rains begin about that time of \ear. The water of .Suisun Ba\-, which is brackish in 

 the simimer and hdl, is gradualh' treshened, therelore, l)\' the inireased stream flow 

 w'hich then begins. In the year 1920, when the teredo epidemic reached its height, 

 and which was a year of very low ri\-er stage in simimer and in the early fall, the 

 waters of .Suisun Bav reached their maximum salinit\' about the middle ot September 

 and, a few weeks later, particularly after the winter rains commenced, the increasing 

 f\o\v of the rivers accelerated the freshening of the water in the upper end of Suisun 

 Bay, so that by the middle of November the brackish water had there been displaced. 

 The seasonal rainfall at the end of December (JuK' 1 to Uecemloer .^1, 1920), was 

 about 40 per cent in excess of the normal. At the time of greatest salinity during 

 that year, the bay w-ater at Collins\ille, just below the mouths of the two rivers, at 

 high tide slack water, was about one-half ocean water; and at low tide slack water 

 somewhat less than one-third ocean water. 



Some evidence was presented in the recent Antioch case, to the effect that about 

 1869 or 1870, under then prevailing conditions before extensive reclamation works 

 had been carried out, the presence of bay water was noticeable by brackish taste as 

 far up stream as Three Mile Slough in the San Joaquin Ri\"er. The presence of 

 brackish water at Antioch, brought up from the bay by the flood tides in the fall 

 months, seems to have been frequently noted, and its presence there in sufficient 

 quantity at certain times in past years, before the question of the effect of the reduc- 

 tion of river flow' by the irrigation draft was raised, is evidenced by the very general 

 use of cisterns by the residents of Antioch. In these cisterns, some of which have been 

 in use 30 years or more, water obtained from the ri\-er in the spring of the year, when 

 the river at Antioch is fresh at all tides, is held for domestic use later in the season. 



