URBAN INFLUENCE ON OZARK STREAM MORPHOLOGY, SOUTH DRY SAC WATERSHED, MISSOURI

Urbanization typically increases runoff and sediment loads in streams which can cause geomorphic changes in channel size and planform. It is important to understand and predict these channel changes since they are often associated with flooding, sedimentation, water quality, and fish habitat problems. This study examines the influence of urbanization on channel geomorphology in the South Dry Sac Watershed (77 km2) located in southwestern Missouri on the Ozarks Plateau. Regression analysis is used to describe the spatial variations in channel morphology of 36 reaches using drainage area, watershed-scale land use and geology factors, and reach-scale buffer and bed conditions. Compared to rural streams, urban streams have straighter channels, shallower pools, and larger dominant channel areas. The magnitude of urban influence on channel form in this study is generally within 20% of the rural channel morphology, however, studies in other regions often report changes of 200% or more. The limited response of these Ozark streams to urban disturbance may be explained by pre-conditioning of the watershed by historical land clearing and row-crop agriculture, presence of cohesive banks with natural gravel armoring near the bed, bedrock bed and/or structural control within karst terrain, and vegetation buffer influence. The spatial distribution of geomorphic resistance factors and history of antecedent disturbance needs to be considered when evaluating downstream changes in geomorphic response to urban land uses in Ozark watersheds.