Roads Surface Erosion Part 1: Summary of effects, processes, and assessment procedures

Introduction Although resource roads provide economic and social benefits, they also pose a hazard to hydrologic, geomorphic, and ecologic processes (Trombulak and Frissell 2000; Gucinski et al. 2001). The ubiquity of roads in natural resource management areas makes understanding their potential impacts a fundamental element in assessing cumulative effects. Even welldesigned road systems can alter streamflow and sediment budgets (Gucinski et al. 2001). Resource roads can increase mass failures and act as chronic or episodic sources of sediment through surface erosion (e.g., Beschta 1978; Bilby 1985; Rice and Lewis 1991; Luce and Black 1999; Fransen et al. 2001; Wemple 2001; Doten et al. 2006). By altering the rate and location of erosion and sedimentation, roads can affect hydrology and geomorphology, as well as negatively impact water quality and aquatic habitat. Roads change natural drainage patterns and alter the amount and distribution of overland flow (Croke et al. 2005). Roads also have the potential to change stream channel networks by concentrating overland flow, which can instigate the development of small channels and gullies, increasing drainage density and stream flow flashiness (Harr et al. 1975; Montgomery 1994; La Marche and Lettenmaier 2001). In addition, roads can directly alter stream channel geometry at engineered road-stream crossings (Richardson et al. 1975), alter animal behaviour (Rost and Bailey 1979), act as barriers to animal and fish migration (Belford and Gould 1989), and facilitate the introduction of chemical contaminants and exotic species to a watershed (Trombulak and Frissell 2000).