| OCR Text |
Show PART V GROUND WATER Juan River basin in the Four Corners area and in the Uinta Basin, the depth to water in wells that tap unconfined aquifers exceeds 300 feet, whereas nearby wells that tap deeper confined aquifers flow at the surface. Water Level Fluctuations Changes in ground water storage owing to changes in natural recharge and discharge and to pumping cause fluctuations of water levels. Rising water levels usually indicate increases in ground water storage and declining water levels usually indicate decreases in storage. Water level records are not adequate to show in detail long term changes in water levels. The following map shows that changes have occurred locally during the period 1961-65. Net rises of more than 50 feet were recorded near Lake Powell, and similar rises are inferred in the vicinity of other new reservoirs, owing to increased bank storage around the reservoirs. Ground Water Storage The estimated storage capacity in the upper 100 feet of saturated thickness of aquifers is about 88 million acre-feet, with a range of estimates of 50 to 116 million. The following map shows the estimated volume of recoverable ground water that is stored in the upper 100 feet of saturated rocks per square mile area; the following tabulation defines the area and total estimated volume of recoverable ground water in these same saturated rocks. Groups 2, 3, 4, 5, 6, and 8 contain the largest volume of recoverable ground water (maximum about 98 million acre-feet) owing to their great extent. However, the water generally is not readily available to individual wells, because the rocks as a whole are poorly permeable and yield the water very slowly. Conversely, groups 1 and 7 contain the smallest volume of recoverable water (maximum about 17 million acre-feet), and the water is generally readily available to individual wells because of the greater perme- ability of these rocks. 20 |
