Information on the processes of erosion and sedimentation, while sometimes sufficient for gross estimates of yield, remains inadequate for modern environmental management. Little is known about sequential processes involved in the systems of erosion and sedimentation, and practice and theory require attention to unsteady or discontinuous erosion and transportation as sediments move from source through channel systems with intermittent periods of storage. While climatic and hydrologic variations markedly affect yield, transport and deposition thresholds of erosion of cohesive materials and sequences of such effects remain unclear. Impact assessment requires understanding of the highly variable temporal and spatial character of sediment behavior, which is often correlative with pollutant behavior.