C6 Slope and Road Drainage

Abstract

Good drainage is a key element in the satisfactory functioning of all roads. In hilly and mountainous areas especially, drainage management is critical to the performance and stability of a road and its structures. Within very short periods of time intense rainfall can lead to landslides and extensive erosion on slopes, while sediment-laden storm runoff can cause blockage to drainage structures and scour of foundations and fill slopes. The control of surface water must therefore be uppermost in the minds of those responsible for the design, construction and maintenance of mountain roads. Slope drainage can be applied both as a routine precautionary measure to improve stability and reduce the incidence of landslides and erosion, and as a reactionary measure to assist in the stabilization of slopes that have already failed. Figures C6.1 and C6.2 and Table C6.1 outline the typical methods of slope drainage found on mountain roads. As a general point, it is recommended that every opportunity is taken to improve the natural drainage of slopes adjacent to roads. This should normally include: Fig. C6.1. Typical slope drainage measures. Fig. C6.2. Typical slope drainage details. View this table: Table C6.1. Types of slope drainage, their function and limitations In order to maximize the efficiency of surface drainage the following guidelines are recommended: ### C6.2.1 Routine slope drainage The main function of drainage in this context is to control surface runoff. A drainage ‘cut-off’ or catch-water drain is the …