If the slope is too steep, the swift water flow causes erosion and maintenance problems. If the slope is too flat, water stays in the ditch and can infiltrate the road base. Water in the base deteriorates the road from within. Lining Erosion creates sediment that is deposited in ditches and water bodies. The greater the erosion, the more maintenance needed.
Excessive erosion can weaken the sides of the road itself.
Ditch lining is the most common way to prevent erosion. Linings can be of natural soil, vegetative, or paved. The material used depends on flow velocity. The following table illustrates the types of lining appropriate for various flow velocities. Engineers use similar tables when designing waterways.