Abstract
In order to study the resistance law of sheet flow, hydraulic experiments are carried out using the slopes of (1) an acrylic plate, (2) a masa sandy loam and (3) a weed, under the condition of constant inflow from the upstream end.
The results obtained by the experiments and other studies arranged in form of the h-q relations are as follows:
1) From the h-q relations, flows over a smooth surface (made of an acrylic plate, wood plate or veneer board) are considered as laminar flow, but this flow is regarded as turbulent when the inflow discharge increases.
2) Flows on a rough surface covered with natural particles or artificial particles are Darcy flow on condition that water flows through the particles, but this flow tends to become laminar when the inflow discharge increases and the depth of flow exceeds the heigit of the particles.
3) Flows on a vegetative surface are Darcy flow when the depth of flow does not exceed the height of vegetative elements, but this flow also tends to become laminar when the depth exceeds the element height.
In conclusion, considering these results from the standpoint of the runoff analysis of a natural basin, it is difficult to explain the behavior of overland flow on natural hillslopes by the resistance law derived from the experiments. Therefore, coefficient k and p of the natural basin cannot be easily decided by the experimental results.
It is said that the definition of the depth of flow in the experiment is difficult, and the sheet flow on natural hillslopes is quite different from those on experimental slopes.
