Floodplain Response to Historical Land Use Change on the Upper Baraboo River, Wisconsin
Krause, Austin Jena
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Since the 1840s, Euro-American settlement of Wisconsin's Baraboo River watershed has had lasting effects on the landscape. This study examines the longitudinal and lateral changes in connectivity on the Baraboo River floodplain. Results show that shear stress, hydraulic radius, stream power, and water surface elevation within the longitudinal profiles each differ from presettlement conditions to modern conditions. The direct impacts include the presence of roads and railroad grades that disrupt the lateral connectivity of the floodplain. Water surface elevations increased since presettlement due to the confinement. Floods as large as the 500-year recurrence interval were found to be unable to overtop many artificially elevated highway and railroad structures, reducing the width of the modern floodplain. Floods with recurrence intervals between 1-10 years are also influenced by cross channel disturbances including bridge crossings and a grade control structure. The bridges constrict flow, and the grade control structure causes a drastic change in water surface elevation, similar to a dam. Flow is slowed upstream of the structure, and downstream flow expansions produce radical changes in velocity and power. Elsewhere, straightening of the river channel may have induced channel incision and promoted increased sediment transport from conversion of natural vegetation to agricultural land use. Understanding the river response to land use change improves future policy decision making with respect to restoration and rehabilitation.