An interceptor ditch is an open channel which was covered in Lesson 4. The military engineer places the
interceptor ditch on the slope above the construction area to catch the runoff and carry it to a discharge point.
Terracing is a control measure designed to dissipate the energy of overland flow before it reaches the construction
area. A terrace consists of a low, broad-based earth levee constructed approximately parallel to the contours. It is
designed to intercept and hold the water until it infiltrates into the soil or to conduct it as overland flow to a
suitable discharge point. A hardy, vigorous turf should be established to hold the soil in place. Vertical spacing
and longitudinal gradients of terrace are given in figure 6-1.
Figure 6-1. Vertical spacing and longitudinal gradients of terraces
This subcourse has mentioned many times the value of turf and other vegetal covers. Turf is used to reduce the
velocity of flow and it retains a certain amount of runoff through interception.