SEDIMENT YIELD CONDITIONED BY GLACIATION IN A RURAL AGRICULTURAL BASIN OF SOUTHERN ONTARIO,CANADA

A sediment budget is constructed for the South Saugeen River, a sixth-order stream basin in southwestern Ontario. Input from eroding glacial embankments accounts for up to 68% of the fine (<63 μm) sediment outputs from the basin. Sediment derived from eroding alluvial banks in the main river contributes approximately 22% of sediment outputs and is approximately equivalent in magnitude to sediments stored in the floodplain. The remaining 10% is derived from sheet and rill erosion of uplands that have been modified by agriculture. However, specification of an appropriate sediment delivery ratio from individual fields to the low-order tributaries remains problematic. Small reservoirs confined by mill dams constructed around the time of land settlement in 1860 store about 3% of the basin sediment inputs. The results demonstrate the importance of downstream, non-alluvial (glacial) sediment sources and can be linked to the model of increasing specific sediment yields with drainage area found in several other river systems of Canada. The high frequency of tall glacial banks in several entrenched river valleys entering the Great Lakes in southern Ontario indicates that the model of dominantly agricultural sediment inputs needs to be adjusted for this region. Key words: sediment budget, glacial conditioning, reservoir sedimentation, bank erosion, agricultural erosion, southern Ontario, Canada.]