History of erosion from pre-European settlement to present and the historiceffects of anthropogenic structures

摘要

Sediment movement through the St. Joseph River Watershed has beensubject to significant human modification over the past 200 years. Thesemodifications include logging, development of agricultural land, dam construction,urbanization, river channel alteration, and the construction of harbor works. The firstmajor dam was constructed in 1850 and 65 large dams now exist in the 12,000 km2watershed. Only 13 % of the watershed now drains directly to the river mouth, anddams form a significant trap for sediment sources from the remaining 87 % of thewatershed. A variety of techniques were used to assess the roles of land-use change and damconstruction in altering sediment movement through the watershed. Watershedsediment yield and delivery under changing land uses were assessed using the SWATmodel. Historic dredging records of the navigable lower river over a 150-year periodwere evaluated to determine sedimentation rates. A two-dimensional hydrodynamicand sediment transport model (RMA2-SED2D) was used to examine the effects ofupstream sediment delivery on the morphodynamics of the harbor and river mouthand to use the dredging data to evaluate the sediment delivery model throughestablishment of historic harbor sediment trapping rates.