首页 / 官方藏书 / River and Canal Engineering, the characteristics of open flowing streams, and the principles and methods to be followed in dealing with them. / 4. Various Types of Weirs.—The type of weir shown in fig. 32 may be varied by steepening or flattening the slopes of one or both faces. Flattening increases the cost but gives a greater spread for the foundations. It may, however, be combined with a decrease in the width of the crest. Flattening of the downstream slope reduces the shock of the water on the floor, but the slope itself, especially the lower portion, has to stand a good deal of wear, and the length exposed to this is increased. Flattening the upstream slope facilitates the passage of floods. The same result is obtained by making the crest slope upwards (fig. 34). In a small stream or in an irrigation distributing channel, a weir may be a simple brick wall with both faces vertical and corners rounded.

4. Various Types of Weirs.—The type of weir shown in fig. 32 may be varied by steepening or flattening the slopes of one or both faces. Flattening increases the cost but gives a greater spread for the foundations. It may, however, be combined with a decrease in the width of the crest. Flattening of the downstream slope reduces the shock of the water on the floor, but the slope itself, especially the lower portion, has to stand a good deal of wear, and the length exposed to this is increased. Flattening the upstream slope facilitates the passage of floods. The same result is obtained by making the crest slope upwards (fig. 34). In a small stream or in an irrigation distributing channel, a weir may be a simple brick wall with both faces vertical and corners rounded.

River and Canal Engineering, the characteristics of open flowing streams, and the principles and methods to be followed in dealing with them. · E. S. Bellasis · 第 4 / 8 章