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Page:Popular Science Monthly Volume 54.djvu/55

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Grisons, were visited by floods of enormous magnitude. Such, was the devastation caused that an appeal was made to the generosity of the nation at large in behalf of the sufferers. This was responded to with such liberality that a large portion of the sum subscribed was put aside for the purpose of improving the water courses permanently. The fact that collective action was necessary in the attempts to control the turbulent streams became very apparent. This being the case, the state was called upon to take charge of this colossal enterprise. In July, 1871, by federal decree, the confederation declared that the correction and extinction of torrents was a matter of public utility, and worthy of the subsidies of the national Government. At the same time the relative burdens of the cantons and the confederation were settled. The importance of the improvement of the water courses and of the wooding of the regions where they rise was recognized in the Constitution of 1874. There the matter was definitely put under federal control and classed with the allied question of the conservation of the forests. The problem of keeping the waters under control in Switzerland ranges from the marshy lowlands to the summits of the passes. In spite of the varying conditions that this range entails, there are certain general principles that bear on all cases where the water is in movement. As the Swiss supplies his want of coal by harnessing his streams, so he makes the water do a large share of the work of correcting its erring ways and preparing itself to be harnessed. This he does by utilizing its power of carrying or depositing stones and soil, according as it is held within narrow banks or allowed to roam at will. As this power depends also on the steepness of the slope down which it runs, he uses this latter factor as well.

When he has got the water courses into what he considers good working condition and one that should be permanent, he tries to clinch matters. This is done by so combining the various conditions of cross-section, slope, and quality of soil that the action of the water is automatic—that is, it brings down no more earth and stones than it is capable of carrying below to safer places where the dangers of floods are small. Whenever the force with which the water moves along is stronger than the cohesion of the soil, erosion occurs. This erosion will continue, the channel of the stream becoming ever deeper, until a soil is encountered whose resistance is equal to the erosive action of the water. As the alluvion is carried on, the slope of the stream will become steeper and steeper the higher one goes. This circumstance would be of much greater importance if the gorges and gullies in which most of the streams run were not so well provided with rock. The power of the water to cause erosion is lessened in proportion to the amount of material it is carrying with