Knowledge of how recharge occurs and interpretation of water-level data in this regard is important from the standpoint of groundwater management as well as basic hydrological understanding. The following excerpt is from a U.S. Geological Survey publication from 1963 (Baldwin and McGuiness, "A Primer on Ground Water").
The use of so much ground water has created new water problems. Under natural conditions the hydrologic cycle tends to be in balance, but man's use of water upsets this balance. Use of water without knowledge of the effects of use or in disregard of them might be called exploitation. In contrast, management of water resources is use
with knowledge of the probable effects and with planning to minimize adverse effects.
Early development in the High Plains of Texas offers a good example of exploitation of ground water. Largely as a result
of heavy pumping the High Plains, Texas is second only to California in its use of ground water; in Texas it is the sole source of supply for nearly 600 towns and cities in the State, and is the principal source used for irrigation. In 1960 Texas withdrew about a fifth of all the ground water used in the United States. Use of ground water is heaviest in the southern High Plains, where it has been stimulated by a long drought. In 1958 more than 1,000 wells were added to the tens of thousands already in existence, and water levels have been declining for years. In this area, the water reserve is gradually being mined.
The principal aquifer in the southern High Plains of Texas, the Ogallala Formation, originally stored nearly 250 million acre-feet of water, a very large quantity. Unfortunately, because of the semiarid climate and flat surface (which encourage evaporation at the expense of runoff and ground-water recharge), the rate of replenishment of the ground water is very low. At the end of 1961 nearly 50 million acre-feet had already been pumped, and the current rate of pumping is more than 50 times the estimated recharge rate. Actually, the rate of withdrawal will decrease gradually as water levels deepen. Because of the cost of the pumping lift, a balance will be struck long before the aquifer is depleted.
Surplus surface water to recharge the ground-water reservoir artificially is not available. Artificial recharge through wells, using rainwater that accumulates in depression is being tried. However, this can help the situation only locally and temporarily. Conservation measures to reduce water waste are being used on an increasing scale.
Strict regulation to limit the amount of pumping would alleviate the situation, of course, but it would effect a complete change in the economy of the area. It is true that reversion to dry farming and grazing would reduce the water demand drastically. Conversion of irrigated land to other uses, principally housing, is already marked in a few areas in Arizona and California, but so far not in Texas. The economy of the High Plains area is firmly based on ground-water mining. Just leaving the water in the aquifer is less beneficial than mining it. It is the rate of depletion which causes concern.
What will happen when irrigation pumping decreases greatly, as it inevitably will, is not certain. Under the laws of Texas, underground water conservation districts have been formed in the High Plains and are promoting conservation measures to increase recharge, take advantage of storm runoff for irrigation and artificial recharge, and reduce waste. Minimum well spacing is required, to spread the pumping and reduce the rate of water table decline.
The problem is very much on the minds of the people of Texas, and more and more thought is being given to the future economic adjustments that will have to be made. Thus the term exploitation, as it implies development without knowledge of the consequences, no longer applies. It is still too early to use the term water management, however.
On the Snake River Plain in Idaho, something opposite to ground-water mining has happened. The Plain is underlain by
a very large body of ground water. It also is an area of little precipitation. But here rainfall and snowmelt in the mountains feed the rivers and much surface water is used for irrigation. Excess irrigation water has filtered into the ground and joined the original ground-water body, increasing the rate of discharge ground water into the Snake River by nearly 50 percent. In this area as a whole, to date, water has not been mined; it has been put in the bank. A tremendous ground-water reserve has been building up and could be managed to great advantage.
For an example of good water management, consider Louisville, KY. During World War II, pumping from closely placed industrial wells increased greatly. From 37 million gallons a day, use rose to 75 mgd, and the water levels in some wells declined nearly to bedrock. The city officials and the War Production Board called on the US Geological Survey for advice. Survey hydrologists in cooperation with local and State agencies mapped the aquifer and studied its rate of natural recharge. It became clear that Louisville was living beyond its means, so far as ground water was concerned.
The adjacent Ohio River was available, but substitution of its water for that from wells would have been difficult or impossible, in view of shortages of critical materials such as pumps and pipe. Conservation measures were adopted as rapidly as possible to reduce the ground-water draft, and filtered city water from the river was injected into wells at two plants where conditions were most critical. The water was injected during the winter, when it was cold, and thus made the wells even more effective for their principal use, for cooling, when the water was repumped the next summer.
The ground-water draft is now stable and water levels have recovered to previous stages throughout most of the area.
