The fallacy of stream equilibrium in contemporary denudation studies

Abstract

Contemporary stream sediment loads are dubious indicators of regional denundation. In many larger basins, sediment storage in the form of colluvium and alluvium appears to be much greater than sediment yield. Analysis of 10 large river basins in the southeastern United States indicates that while upland erosion was proceeding at about 95 mm/100 yrs, sediment yield were only about 5.3 mm/100 yrs, a delivery ratio of about 6 percent. Similar sediemt budgets exist int he Driftless Arca. In both regions much of the modern erosional debris is stored int eh stream systems as massive deposits in streams and valleys. Some of these deposits are presently being eroded and are now themselves sources of sediment yields. However, the transport of sediment is significantly impeded by extensive reservoir impoundments, especially in the southeast. Thus, present sediment yields may correlate poorly with upland erosional processes or phenomena such as lithology, climate, vegetation, and land use. Instead, sediment yields may be a reflection of channel efficiency, soil texture, basin morphology, and channel or bank erosion.