Indian Storage Reservoirs with Earthen Dams; Being a Practical Treatise on Their Design and Construction (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1913 Excerpt: ...to provide for contingencies, it will be advisable to allow 25 per cent, over the observed maximum flood when estimating the discharge for which provision should be made. It is far safer to rely upon the results of observation than upon a mathematical formula, for the intensity and amount of the rain are not fixed quantities, nor are the original state of wetness of the ground (vide paragraphs 17 and 18) and the rate of travel of a storm always the same, but it is upon these variable factors that the variation in the rate of the flood discharge of any particular catchment entirely depends. In the case of a reservoir, however, it is not necessary, as in that of a drainage work, to provide for the absolutely maximum rate of flood which may occur, for the storage capacitor of the tank will act as a moderator of the intensity of the discharge, as is explained in paragraphs 182--184. Where drainage areas are liable to be visited by cyclones, it is not practicable to determine exactly what will be the discharge resulting from such storms, as their intensity is so abnormal. In such cases it is best to provide liberally for the ordinary maximum floods, and, in addition, to allow for these abnormal ones by designing breaching sections (vide paragraph 75) and safety flood cuts (vide paragraph 165). In paragraph 28 it has been stated that in twenty Bombay tanks the average cost of the waste-weir is only 945 per cent, of that of the whole reservoir. As a proper provision for this essential to safety is comparatively so cheap, and as the results of the bursting of a dam may be so disastrous, it is always more prudent to err on the side of safety and to make ample allowance for floods than to run any risk of failure by having insufficient waste-weir discharging capacity....