Annex 3A: Guidelines for Local Gravel Road Rehabilitation 443 fully functional, effective and complete. Earth side drains Longitudinal drains are required along the side of the roadway to collect and transport water running off the cross-fall of the road surface. They should ideally resist erosion, be self-cleaning and discharge into established water ways or other areas where surface water run-off water may be accepted (adapted from IBRD, 2005). Ditches at the side of roads should ideally be wide and shallow. Minimum depth of ditches should be 0.3 to 0.4 m below the roadway, with a flat bottomed profile. For flat bottomed ditches, the side slope and back slope should ideally have less than 1:4 ratio. Where this is not possible, they should have no less than 1:2 ratio (IBRD,2005). Figure 4. Standard details for cross drain, earth ditch, and grouted riprap lined ditch