Abstract
As an erosion and sediment control method during and after reclamation work for sloping land, the authors proposed a graded temporary levee method to help with sediment control across a field slope in an effort to try to reduce the soil loss from field lots.
In this paper, the actual conditions causing sedimentation along the graded temporary levee were studied based on the results of a field test which was carried out in various sets of field slope degrees and levee gradients.
The results obtained were as follows.
1) The upper limit of the temporary levee gradient causing sedimentation was from 4 to 5 degrees, according to field slope of from 6 to 10 degrees (Fig. 4).
2) Along the high gradient temporary levee under the upper limit, sedimentation seldom progressed very effectively, but the temporary effect of sedimentation was expected in heavy storms soon after the construction of temporary levees (Figs. 5 and 6).
3) Temporary levee gradient causing effective sedimentation was under about 3.5 degrees for thefi eld slope under 10 degrees (Fig. 7), and effective sedimentation was caused in orthogonal sediment fans against temporary levees.
4) Along the low gradient temporary levee under about 1 degree, surface drainage was restricted because of irregular sedimentation, and as a result, levee failure occurred along the lower side of the temporary levee.
5) Grain size distribution of the sediment tended to be finer as the temporary levee gradient was increased over 2 degrees (Table 1).
6) Sedimentation phenomena along the graded temporary levee seemed to be complexly affected by the sediment transport characteristics of the various size grains and the shear stress which changed every moment and varied with location.
7) The most suitable gradient to help effective sedimentation and adequate drainage seemed to be from 2 to 3 degrees, with a field slope of 6 to 10 degrees.
