ABSTRACT
Sediment origin and suspended sediment load data are examined for the large (43,000 km2) drainage basin of the Red Deer River in southcentral Alberta. Most of the basin lies within the semi-arid prairie environment though the headwaters are in the moist foothill and mountain section of the province. Fifty percent of the river’s mean annual discharge of 70 m3/s are derived from the headwaters region, or about six percent of the total basin area. The remaining runoff is derived from the prairies. Sediment supply from the headwaters region is comparatively small, accounting for perhaps 12 percent of the total suspended sediment load, and much of the prairie region contributes neither runoff nor sediment to the river. Detailed observations of erosion rates (4.50 mm/yr) and estimates of sediment yield (8,217 tonnes/km2/yr from a region of badlands, that form about two percent of the basin’s area, shows these supply about 90 percent of the total suspended load. Parallels are drawn between this situation and the partial area concept of runoff. It is concluded that the common practice of determining regional erosion rates is meaningless.
