This paper presents a comprehensive estimation of the sediment-control effect by sabo dam infocussing on the slope gradient of the deposited sediment at sabo dams. The field data at five dams in the Koshibugawa, a tributary of the Tenryu River were used for the analysis. Hydraulic-model experiments were also carried out to clarify the effects of the sediment concentration in flow of water on the slope gradient of the deposited sediment at sabo dams.
The following conclusions were obtained as a result of this investigation:
(1) In the case of a sabo dam with relatively large capacity has been built in upstream, little or only a little degradation of the river-bed can be seen in the downstream sabo dams after floods.
(2) The newly-built big sabo dam, however, gives a significant change in the period for restore the slope gradient of the deposited sediment after floods at the downstream sabo dams, because of the large impoundment of sediment and the big change in grain size at the new sabo dam.
(3) When the sedimentation-form is expressed by a quadratic equation,
y=
ax+
bx2, a linear relationship is observed between the coefficients
a and
b.
The coefficient
b reached the maximum several years after the new construction and then gradually decreased.
(4) The comparison between the results of our experiments and the given values in previous literature shows that the dimensionless slope gradient of the deposited sediment, slope gradient of the deposited sediment/ original river-bed slope gradient, is an increasing function of the concentration of debris flow as a first approximation, and that the slope gradient of the deposited sediment is substantially half the original gradient of the river-bed at a lower concentration of debris flow.
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