Theoretical considerations on the modes of surface run-off and erosion. Foundations for control. Application: determine spacing between anti-erosion devices

Abstract

The violence of rainfall acts upon the conditions of the soil surface, changes them and provokes run-off. The intensity and duration of rainfall are important factors of run-off.
The soil characteristics which affect run-off are as follows: the condition of the surface (liable to change under the action of downpour), its composition (grade, quantity of organic matter) and its hydrodynamic properties.
The run-off of waters at the surface of the soil was studied mathematically with the help of DARCY's method and the stream flow equation. The rational formulae obtained in a stable system show that:
- run-off and erosion depend on the length of the plot, the quantity of rainwater and the likelihood of infiltration of water into the soils,
- erosion also depends on the intensity and the duration of the rain, the slope and the roughness of the soil.
The hierarchical organization of these factors helps to determine the appropriate means of fighting these phenomena.
A method (PRI) which allows the spacing of anti-erosion devices to be determined has been suggested and compared with the various present methods. It takes into account a risk factor, the intensity of rainfall over thirty minutes and the roughness of the soil (vegetation and soil surface).