C7 Erosion control

Abstract

An important element in roadside slope management is the preservation and encouragement of the natural vegetation. However, the effects of road construction on erosion can often extend well beyond the right of way. In mountainous terrain, road construction itself often facilitates access to areas of forest that then become logged for timber as development takes place within the wider road corridor. The gradual depletion of forest cover can lead to increased runoff, causing slope erosion, gullying and downcutting in stream channels, which eventually increases the incidence of landslides. This process may be exacerbated by the indiscriminate dumping of excavation spoil during construction, creating debris hazards downstream (e.g. Kojan 1978; Hearn 1987; Zurick & Karan 1999; Hart et al. 2002; Campos et al. 2010 with respect to road corridors in Nepal, the Philippines and Brazil). However, even where these effects are minimized through good land use planning and engineering management practices, there is usually a significant potential for erosion to occur on unprotected cut and fill slopes, in stream channels and at other drainage discharge points (Section C6). Erosion on roadside slopes is sporadic and difficult to predict since it is related to rainfall events, slope drainage patterns and the characteristics of the ground. The largest volumes of erosion are usually generated from short-duration, intense rainfall events. Methods used to combat this erosion are described and discussed below in the context of slopes and streams. ### C7.2.1 Options Broadly, there are two main options for erosion control: A combination of the two is also often used. On low-cost roads, the desire to minimize costs may lead to an emphasis on the use of bio-engineering (Section C7.2.4). However, planting schemes can take some time to establish and should …