| Three years of detailed measurements of erosion and sediment discharge in the 1.74 km('2) drainage basin of Lone Tree Creek, a small stream 14 km northwest of San Francisco, showed that debris slides and flows from colluvium-filled swales are the most important erosional agent and account for most of the current sediment yield from the basin. The bare scars are loci for sheetwash and gully development; they refill by backwearing of slide scarps and by soil creep. During the study period, only 53 per cent (2068 t/km('2)) of all sediment mobilized was discharged from the basin; the remainder was stored in slide scars, on footslopes, and in gully and channel banks and beds. Sediment is removed from storage by storms with recurrence intervals greater than 10 years. Comparison of present rates of sliding and refilling suggests that slide frequency has increased approximately tenfold in the past 50-150 years, and that slides are currently mining relicit colluvium. |
