OCR Text |
Show Importance of Local Factors Regional Possibilities For these reasons, with respect to both surface waters and ground waters it is extremely im- portant that we know for each locality where water problems occur, the factors affecting sup- ply, development, use, management, and protec- tion, and what may be done to modify such factors or adjust use to their limitations. These local factors are the significant things, not broad Nation-wide generalizations. Broad generaliza- tions are only summaries of the state of knowledge at a particular time, and are tentative. Such generalizations may be made to guide action, which is always a problem of today and cannot wait for the more definite knowledge that will result from the investigations continually in process. The principal draft on ground water is exces- sive pumping, especially pumping by modern high-powered, deep-reaching pumps for large- scale municipal, industrial, and irrigation use. Only about one-sixth as much water-25 billion gallons a day-used at the present time in the United States comes from ground water as comes from streams and lakes. However, that sixth is concentrated over particular reservoirs and in many areas exhausts the local ground water sup- ply at a greater rate than the rate of natural recharge. To meet this problem three lines of action are indicated: first, artificial recharge of affected reservoirs to the extent that local conditions and the devices of man permit; second, management of the reservoir's recharge area to insure maxi- mum infiltration of precipitation; and third, planned, rational use of the total amount thus made available so as to maintain a balanced water budget. These lines of action must be based on thorough study of all pertinent factors present in each particular affected reservoir, because no two reservoirs are identical and the effects of remedial measures may vary from one reservoir to another. And because ground water is a "hidden asset," these studies are more difficult than are those pertaining to surface water. Full knowledge of the country's potential ground water resources awaits the comprehensive surveys being recommended. But the able work of the United States Geological Survey and other agencies has provided a basis for indicating some- thing of the relationship between surface and ground water. This is shown in the accompany- ing map compiled by E. H. Thomas for the Con- servation Foundation. Particularly in the great basin of the Mississippi and its tributaries, the map suggests the possibility of combined manage- ment of surface and ground water resources. The Coastal Plain along the Atlantic and Gulf Seaboards is in general the best watered region in the United States. Excepting only in its west- ernmost part, in Texas, the coastal plain is pre- vailingly humid and warm, with precipitation about equal to, or commonly exceeding, the evap- oration and consumption of water by vegetation in all seasons. This region is perhaps potentially the most productive ground water region in the United States. Although some of its areas are almost fully developed, very large undeveloped ground water sources remain in most parts of the area. The question arises as to whether, in connec- tion with the future development of the region, comprehensive plans should not be made for utili- zation of the large undeveloped ground water resources in conjunction with surface waters to supplement the supplies of areas in which, due to concentrations of industry and population, the water resources have been fully developed. This may mean industry and population locating ad- jacent to undeveloped reserves, or water being conveyed larger distances-a matter of economy. Surface water supplies in the region are rela- tively large, although they vary rather widely from season to season, and floods are troublesome at numerous places. Serious erosion of the higher lands, organic and chemical pollution from sources upstream and in the region, and salt water encroachment into tidal reaches during low- flow periods all present stream management problems. 114 |