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Show cubic feet per second average surface flow of the Nation's streams falling 1,000 feet does the work of more than 175 million horsepower, night and day, all of the time. Thus the slow action of the erosion and solu- tion by water has given us the topography of our mountains, valleys, and drainage basins as we know them. Knowledge of geology and the man- ner in which valleys have been created is of great value in determining the location and avail- ability of ground water. In some localities ground water flows a thousand miles through porous sandstones, in others through the porous valley fill deposited by the changing course of the river, or the porous deposits left by the continental ice sheets during the glacial epochs in northern portions of the United States. Elsewhere ground water is found in cavernous limestones, or lavas and other fractural rocks. But always there must be an intake area where precipitation falling on the surface of the land can find its way into these underground aquifers, thus to percolate slowly to lower ground water basins or channels or to emerge again on the surface as rising water. Man's use of the land by felling forest, clear- ing land, and turning of the soil has done much to accelerate erosion. Fortunately knowledge now exists of corrective steps that can be taken by effective land management practices. The total problem is great because the areas are so large and so much of the land is in so many farm, grazing, and timber ownerships, all requiring training and cooperative effort to produce the desirable conservation results which should be attained. Storage: The First Principle We think of the Great Lakes as the greatest natural storage facilities for fresh water in the United States. They hold the equivalent of 2 y2 years' average rainfall over the whole of the Na- tion's land area, or 8 years' average runoff to the oceans. But the great unseen ground water reser- voirs, which, provide the water for the country's shallow- and deep-driven wells, are larger; they constitute the largest fresh-water storage naturally available to the Nation. Storage of water is of first importance because: 1. Rain does not fall regularly throughout the year or equally from year to year-it swings from tremendous downpours to periods of drought. 2. Water that falls as snow on frozen ground neither sinks in, nor runs off, until the return of the warm sunshine and rains of spring. 3. Man's need for water is not spread equally over the whole land due to his concentration in industrial and agricultural areas. In addition to that needed for forest, range, pasture, and crop growth, it is also a necessity in navigation chan- nels, urban areas, and centers of industry. 4. Some of man's needs require steadier sup- plies throughout the days and years than rain- fall would give, while others require supplies that can be controlled and delivered at specific hours. For all these reasons, man must provide intel- ligent management of his water resources con- tinuously from the time the raindrops strike the earth. Storage Begins With the Watershed All rain falls on watersheds, that is, on areas that slope toward a common land trough in which the runoff from rainfall becomes first a rill and then a brook and then a tributary stream and finally a river. Ultimately these rivers may con- verge into larger rivers, and these, with their tributaries, carve great river basins. Each one of us lives in a small watershed. Citi- zenship in that watershed makes us citizens of the larger river basin of which it is a part. Each one of us should feel a direct responsibility for the cooperative management of our watershed, to make sure that it plays its proper part in storing the water which falls upon it. This essential storage begins in the soil itself, if the soil of the watersheds is properly cared for. There the water is initially suspended within reach of root systems, constituting the temporary storage by which vegetation, both crop plants and natural cover, is sustained. The quantity varies greatly each year. Natural suspended water 110 |
