Seasonal sediment yield patterns of U.S. rivers

Abstract

The sedihydrogram is a double log plot of mean monthly sediment yield against mean monthly water yield. A line connecting consecutive months indicates the seasonal rhythm of erosion and runoff occurring in a drainage basin. Sediment regimes seen on the sedihydrogram are explained by a model that relates basin hydrology to the dominance of common air masses. Mediterranean and continental climate and erosion regimes are well expressed in U.S. rivers. Mediterranean regimes in the western United States have a dry summer and a wet winter with strong seasonal contrasts between early wet season floods and less turbid flow events later in the wet season. Large sediment yield values may be expected from basins in which seasonal desiccation alternates with heavy rains. Continental regimes in the central and eastern United States have a water yield event in late winter or early spring with a low sediment concentration. Summer storms produce high concentrations and a low water yield. The summer component of the sedihydrogram is dominant in dry regions but minor in humid areas, where vegetation offers effective protection from storms. Land use factors influence sedihydrogram patterns. Basins in eastern humid states have a sedihydrogram typical of arid regions if strip mining or urbanization has had an important effect on the basin hydrology. Most climate regimes show a seasonal shift in the parameters of the sediment transport curve, so that an analysis of seasonally grouped data results in improved equations for relating sediment movement to environmental controls. The prediction of sediment yield requires that separate consideration be given to those factors affecting runoff and those affecting sediment concentration.