| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 1993: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1992: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 1991: ¥600,000 (Direct Cost: ¥600,000)
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| Research Abstract |
A large number of channels or rills are formed on a bare slope about the same time as surface flow is generated, and the sediment discharge rapidly increases as the development of rills grows.
The purpose of this study is to investigate the relationship between the rill patterns and soil run-off, At first, we describe an experimental studies of the process of growing rills which are formed on composite granite soil which is called "MASA-DO", by supplying artificial rainfall. We photographed the changes of rill patterns in plane and cross sectional patterns of rills each elapsed time and also measured sediment yield.
As rill networks have a irregular and complex pattens, it is difficult to express the patterns numerically by the classic geometircal concepts. The complexity of rill patterns was expressed numerically using the concept of fractal dimension. As a result of this analysis, the change in fractal dimension in each elapsed time was closely related to the change in sediment dischar
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ge and water discharge from the slope.
In addition to the fractal analysis, the applicability of Fourier analsys to plane patterns of rill was also considered. the degree of complication of rill patterns is described as entropy by applying the geometrical concepts of Spectrum. The entropy of rill patterns can be calculated from the power spectrum which can be obtained by decomposing the rill patterns into the several single harmonic function. the entropy and the fractal dimension of rill patterns were closely related to the number of bifurcations of the rill.
Subsequently, the process of formation of rill patterns was simulated with the aid of a random pattern model (for example, Diffusion-Limited-Aggregation model or DLA model), which is used in the fields of fractal geometry. As rill patterns have highy involved one, the classical simulation model, such as a random walk model which could be explained the patterns of river networks, could not be explained the rill patterns well. The concept of fractal geometry is the effective method of the quantification of natural figures, so rill patterns can be simulated by such method that is based on the fractal geometry. As a results of the simulation, the simulated patterns were very similar to the rill patterns that develop on-the-spot slopes. Less
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