. Studies in French forestry . Forests and forestry. ROCK DRAINS 161 The drains must be large enough to insure the prompt runoff of water. Under exceptional circumstances the French have managed to dry ground to a great depth, sometimes up to 10 to 13 feet, but the expense is much greater. First-class drains are generally built where the slope is steep, in order to assure rapid runoff. They are less likely to be dislocated by soil movements. At the head of drains little walls are constructed as Fig. 12. graph.) - Paved drains at Bastan (Hautes-Pyrenees). (French official photo- When th
. Studies in French forestry . Forests and forestry. ROCK DRAINS 161 The drains must be large enough to insure the prompt runoff of water. Under exceptional circumstances the French have managed to dry ground to a great depth, sometimes up to 10 to 13 feet, but the expense is much greater. First-class drains are generally built where the slope is steep, in order to assure rapid runoff. They are less likely to be dislocated by soil movements. At the head of drains little walls are constructed as Fig. 12. graph.) - Paved drains at Bastan (Hautes-Pyrenees). (French official photo- When the drainage water is abundant it is often united in a paved trench built in the valley bottom to carry the water under the dams. Where the soil movements are due to a leaky canal it is often better to stop the cause of the infiltration rather than to take up the expensive work of drainage. To prevent running water from eroding the soil it is often advisable to collect it in little canals, about 20 inches in depth, which follow the slope and which are filled with little stones or fascines. These canals can be replaced by paved drains if the earth is in movement. Trees are planted. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Woolsey, Theodore Salisbury, 1879-; Greeley, William Buckhout, 1879-. New York : Wiley
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectforestsandforestry
