45 



the flamage, amounting to more than 825,000,000 already caused l)y this borer in the 

 upper Bay and straits region, is a matter of some significance. And the largely in- 

 creased area over which this protection will lie effective with the lower barrier site, 

 as against one higher up, adds additional weight to the argument for that site. 



A properly located, properly designed salt water barrier at the Narrows, below 

 San Pablo Bay, will con\ert both San Pablo and Suisun Ba\-s into fresh water bodies 

 with a combined surface e.xtent of about 110,000 acres. The Sacramento and San 

 Joaquin Ri\-ers will annually discharge into these bays enough water to replace their 

 water contents from two to over ten times, so that they can lie depended upon to 

 furnish the water that will enable these modified bays to be used as a reserx'oir of 

 fresh water. The barrier, it may be assumed, will be so arranged that in winter the 

 Hood flow of the streams can find [passage through automatic flood gates. These might 

 be arranged to operate on a concrete sill placed below the Narrows where it is 

 3 to 4 miles wide, and should have a capacity such that piers between openings will 

 obstruct the flowing water to the extent of only 2 to ,i inches. In addition to the flood 

 gates there should be a second set of gates, preferably at the upper edge of the concrete 

 sill, pro\iiled with power control. These gates would then be used to hold the summer 

 water abo\e the barrier (that is, in the two bays) at about present ordinary lall high 

 tide elevation, thereby effecting the proposed conversion of these bays into a great 

 fresh water reservoir. The annually available contents of this reservoir, from an ordi- 

 nary high stage about () feet abo\-e low tide down to say one foot abcjve low water, 

 will be aliout .SOO.OOO acre feet. This amount is, however, not all the water that can 

 annualh' be drawn from this reservoir, because to this amoimt should be added what- 

 ever the ri\ers are discharging, less, of course, a small amount required for lockages 

 at the barrier. Moreover, the reservoir will be full every year about July 1st and it is 

 only the late summer and fall demand of the irrigator which will deplete its contents. 

 Such a supply, con\eniently tapped from the banks of any of the channels, natural 

 or artificial, in the delta region ol the San Joaquin and Sacramento Ri\ers will ade- 

 cjuateK' meet the requirements of more than 300,000 acres of delta lands under intense 

 cultivation as well as the needs of more than 100,000 acres of mainland bordering on 

 the delta. Furtheriuore, the sloughs extending from the bays into the salt marshes 

 would be permanenth" filled with fresh water, affording an abundant supply with which 

 to freshen the land and make it available for farming. 



The reservoir created by the barrier can be so regulated as to surface elevation 

 that during the summer and fall there will always be from one to five feet more water 

 in the bays and in the lower rivers — up to Sacramento and up to Stockton — than now 

 obtains at the rivers' low tide stages. In the reservoir there will be only a one-way cur- 

 rent and this current will be sluggish except when the rivers are at high stages. Navi- 

 gation will, therefore, get some benefit both as to depth of navigable water and elimina- 

 tion of uncertain bay currents. 



There will be no more nor less silt brought down into the bays then than is now 

 brought down by the rivers. This silt moves at flood stages. Under present conditions 

 it meets the checking influence of the up-stream current at flood tide, it is dropped at 

 slack water, and its deposit is encouraged by the admixture of ocean water which acts 

 in some measure as a precipitating agent. The probability is that rather less than more 

 silt will remain in the two bays, if converted into fresh water lakes, than at present. 



The salt water barrier, if placed below San Pablo Bay, will, as already intimated, 

 assist in keeping down the elevation of the flood planes of the two upper bays and of 

 the lower rivers. This results from the large reservoir capacity above the barrier. 

 During the high stages of the ri\ers, which occur in winter and in early spring, the 



