Toward a uniform theory of clastic sediment yield in fluvial systems

Sediment is delivered to streams by creep, slope wash, rill and gully erosi on, and collapse of oversteepened banks. The first three of these operate o n all transport-limited slopes. Their efficacy varies directly with precipi tation (or runoff) and inversely with vegetation cover. Sediment yield from these processes is also likely to increase with slope angle and, in the ca se of slope mash and rill erosion, with rainfall intensity and slope length . Sloughing from oversteepened banks, however, occurs where rivers are active ly cutting into valley sides. The frequency of occurrence of such locations increases with the mean slope angle, and the frequency of collapse increas es with runoff. Thus, this process is likely to be dominant in mountainous areas with high runoff. Expressing these effects analytically leads to a tentative general relation for specific sediment yield. If we had sufficient knowledge of the various parameters involved, this relation could be integrated over a basin to obt ain the total yield. At present, however, its main value is to draw attenti on to the numerous assumptions implicit in many much simpler equations in c ommon use.