Abstract
The backsand phenomenon in a steep slope straight riverwith a compound section was experimentally studied and the following facts were found:
1) In the compound section of a straight and winding rivers, the eddy region appears at the connecting position of rivers and reservoirs, that is on the high-water channel of the direct downstream station of the jump. Owing to this phenomenon, the backsand mechanism differsfrom the rectangular section case and backsand occurs only with the undular type. The beginning of deposition moves more rapidly in the straight river case with a rectangular section and its speedlessens in order of the winding river case and the a straight river case with a compound section. And reversely, the front of the delta moves slowly in the former order. This order is same as the order for the area of the eddy region.
2) The vaious sedimentation characteristics are similar to thosein the case of the rectangular section except that the sedimentation begins at the downstream station separated from the jump in case of a large eddy area owing to the existence of the eddy region.
Assuming the formation rule for delta sedimentation based on thetest results, the movement at the beginning point of deposition and the front of the delta with a lapse of time were theoretically estimated.
3) The area of the eddy. region was affected mainly by dr (dr=d/h1, d: The difference of the elevation between high-water and low-water channel beds, h1: the depth of the low-water channel at the upstream station of the jump) When dr is less than the critical value, the eddy region disappears, and when dr is larger than the critical value, the eddy region expands its area with an increase in dr.
This critical value is shown by the equation that is strictly the function of the Froude number.And then, the mean width of the eddy region was theoretically estimated by the momentum equation.
