Page:Popular Science Monthly Volume 13.djvu/305

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291
WATER-SUPPLY OF RIVERS.

this, white poplar and white birch spring up, which, however, are liable to be burned at any time, as the fire runs freely through all deciduous timber in the spring, before the leaves are out, or during a very dry time in summer.

It is generally understood that the clearing away of the forests has the effect of causing low water during the summer season, and the reasons given for it are, the more rapid evaporation of water from the soil, on account of the greater exposure to the sun in cleared than in timbered land, and to this may be added the more rapid drainage, particularly in sandy soils, after the rotten logs, leaves, and other absorbents, have been removed; and it is also claimed that more rain falls upon a section of country when it is timbered than after the land has been cleared. The first of these reasons is undoubtedly correct, and there is a great deal to show that the second is correct also, though I do not think we know enough about the subject to justify us in stating, as a scientific fact, that the amount of rainfall is affected by the growth of timber.

I have never known the existence of the spruce "duff" to be recognized, as a fact of any importance, in governing our water-supply during dry seasons; but, unless I am greatly in error, it is a matter of the greatest importance, and the destruction of the "duff," with the destruction of the forests, will prove as damaging to our streams as the increased evaporation caused by the greater exposure of the land to the sun.

The waters from this immediate section of country flow into Lake Champlain, and thence into the St. Lawrence River. The country around the principal feeders of the Hudson River is almost identical with the country described above, and the same causes that affect the water-supply of the Saranac and Ausable govern the water-supply of the Hudson.

The water-supply of the Hudson is a matter of very great importance to the people of New York, and any facts tending to throw light upon the natural laws governing it should be received with interest by the intelligent people whose health, comfort, and prosperity, are partially dependent upon the quantity and purity of the water in this noble river. Hundreds of square miles of the country upon whose drainage the Hudson is dependent for its supply of water is covered with this "spruce-duff," which, in the early spring, is a solid body of ice, holding untold millions of gallons of the purest water, to be slowly thawed out and given up to this river during the summer. In many places, and in most seasons, part of this ice lasts through the whole summer; in most places it lasts well into the summer, and even after the ice is gone the "duff" absorbs and stores away the rain, and, like a prudent housewife with her confections, gives up her treasures in such a way as not to injure the health of her children with her lavishness, nor exhaust her larder before a fresh supply can reasonably be expected.