Physical measures are structures built for soil and water conservation. Some principles should be considered. They should aim to
- increase the time of concentration of runoff, thereby allowing more of it to infiltrate into the soil;
- divide a long slope into several short ones and thereby reducing amount and velocity of surface runoff;
- reduce the velocity of the surface runoff;
- protect against damage due to excessive runoff .
In most systems any physical measure can be built – check dams or contour ditches, for example .
For example, in the Gina River catchment in Ethiopia, walls and terraces are used. Both serve as control structures to prevent soil erosion processes - a major problem in this drainage basin.
Terraces are explained in more detail on the following learning page.