Water-power; an outline of the development and application of the energy of flowing water . the velocity, without giving thedam a profile greatly in excess of that called for by considera-tions of stability. Should such a dam be built under theimpression that water going over it would reach the bottomwith a low velocity, dispositions necessary to secure the bottomfrom abrasion would be likely to be neglected, to the increaseof the risk of disaster. This form of dam would be improvedby giving the tread between two consecutive steps an inclina-tion up-stream, forming a basin for stilling the com
Water-power; an outline of the development and application of the energy of flowing water . the velocity, without giving thedam a profile greatly in excess of that called for by considera-tions of stability. Should such a dam be built under theimpression that water going over it would reach the bottomwith a low velocity, dispositions necessary to secure the bottomfrom abrasion would be likely to be neglected, to the increaseof the risk of disaster. This form of dam would be improvedby giving the tread between two consecutive steps an inclina-tion up-stream, forming a basin for stilling the commotion andmoderating the shock of floating bodies. It is to be doubted,however, whether any form of dam has less to recommend itfor adoption than this. It will appear later that no form ofdam suffers more severeh than this from ice and logs. Inclination of Top of Dam.—It is usual to give the top ofthe dam an inclination, rising toward the down-stream side, tofacilitate the passage of ice and floating bodies, the portion 14, rising from 12 to 30 inches, according to the size of. Fig. 14. the bodies to be looked for. Blocks of ice on northern riversmay float to a depth of 40 inches, but such blocks would notmove at all unless there was some depth of water going overthe dam. Ice is liable to move in masses which make it DAMS CURVED IN CROSS-SECTION. 33 formidable even at low velocities. This arrangement is to berecommended for a low dam, but the necessity for it diminishesas the height of the dam increases. It is manifest that in thecase of a high dam, in any stage of water such that floatingbodies could strike the dam, they must approach it with avery low velocity. Dams of rectangular outline have sometimes been builtwith a sloping bank of earth or loose stone on the up-streamside. Whatever advantage may be expected from this arrange-ment, it certainly has one serious objection. It shoals thew^aterway approaching the dam, and increases the velocity withwhich floating bo
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Keywords: ., bookcentury1900, bookdecade1910, booksubjecthydraulicengineering
