| OCR Text |
Show From the foregoing, it can be seen that it is not possible to remove ground water from the valley fill for consumptive use without affecting streamflow. It is possible, however, to make more effective use of the water resources by " borrowing" water from ground- water storage during periods of peak demand and " paying back" ( in diminished streamflow) during periods of low demand. The details of such a water- management plan are beyond the scope of this report. Detailed studies for such a plan should include tests to determine the aquifer coefficients at the proposed pumping site; the aquifer coefficients given in this report for the valley as a whole may not be applicable to a particular site. The preceding discussion concerns withdrawals of ground water for increased consumptive use. Virtually all the irrigable land in the valleys is already irrigated, however, from surface- water sources. Pumping ground water to replace surface water for irrigation would not be an increase in consumptive use. Indeed, such a practice would doubtless save water, because evaporation losses from canals would be reduced. The cost of constructing wells and operating pumps, however, would increase the cost of water to the irrigator. Outside the valleys, in the areas underlain by consolidated rocks, the low flow of the streams is sustained by ground- water discharge, and increased withdrawal of ground water would decrease the natural discharge. Existing methods of estimating the effects of pumping wells on nearby streams, however, are not applicable to the consolidated rocks; therefore, no quantitative estimates of the effect of increased withdrawal of ground water from the consolidated rocks can be made. 47 |
