OCR Text |
Show PART V GROUND WATER Effects of Ground Water Withdrawals Under existing conditions of ground water development, effects of withdrawals are not widespread and are limited for the most part to local interference between discharging wells. However, any large scale development in the region might ultimately cause widespread effects on the water resources regimen. The most significant effects could be an ultimate decrease in streamflow, changes in chemical quality of the ground water, and decrease in natural discharge from shallow aquifers. A close relation exists between ground and surface water resources. During periods of maximum overland runoff, water moves from stream channels into adjacent aquifers as ground water recharges. Conversely, during periods of minimum overland runoff, ground water moves into stream channels to augment streamflow. Any large scale development of ground water in the basin, therefore, would ultimately result in decreased streamflow. For example, more streamflow would be lost during high runoff periods to replenish depleted ground water supplies, and less ground water would be available to support stream- flow during periods of low flow. In some areas, aquifers containing fresh water are overlain or underlain by aquifers containing saline water. Large withdrawals from the fresh water aquifers would tend to decrease the pressure in those aquifers, thereby inducing recharge from the saline water aquifers and ultimately causing deterioration of the fresh water aquifer. Large increases in ground water withdrawals may reduce consumptive use by nonbeneficial vegetation. Phreatophytes grow unchecked in many parts of the region, particularly in alluvial plains. If increased pumping resulted in a significant lowering or fluctuating of water levels in the root zones of phreatophytes, consumptive use by these nonbeneficial plants would be greatly reduced. 23 |