Journal of the Japan Society of Erosion Control Engineering
Online ISSN : 2187-4654
Print ISSN : 0286-8385
ISSN-L : 0286-8385
On Optimum Iuclination-Angle of the Spillway-Crown on the Steel-Dam
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1981 Volume 33 Issue 3 Pages 1-7


In this paper we describe an experimental study on the inclination-angle of the spillway-crown, which the sediment overflowing a Sabo-Dam are letten fly away maximum distance.
1. It seems to be quite all right to consider that the sediment which leave the spillway-crown, falling in the parabolic motion.
2. In figure-1, the relation of the falling distance (X) and other factors may be formularized following equation:
where υs is the velocity of the object on the point B, S is the length of slope (from A to B), α is the angle of slope, g is the acceleration of gravity, Y is the height of Dam. Then, We are able to rewrite this equation as follows:
υs=L/[2⋅g-1⋅cosα(H⋅cosα-L⋅sinα)]1/2, L=X-S⋅cosα, H=Y-S⋅sinα
where υs′ means the caluclated velocity by the experimental datd.
3. The velocity of the spherical objects which are roll down at the slope on the point B is estimated byfollowing equation:
where υ0 is the velosity on the point A and this υs is the theoretical value.
4. Useing several materials and sizes experiments were done and obtained the velocity ratio υs′/υs
such as following:
Steel ball: 89-98% average 96%
Porcelain ball and Glass ball: 80-95% average 91%
Cobbles in the river bed: 69-89% average 79%
5. We tryed same experiments which several sizescobbles were throwed into the flow of overflowing the Sabo-Dam in practice and made observation the same phenomena, above-mentioned.
From the results of our experiments, it may be conclude that the optimum angle of inclination for spillway-crown of the Steel-Dam seemes to be suitable for 25-35 degree.

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