Natural channel designs often incorporate rigid in-stream structures to protectchannel banks, provide grade control, promote flow deflection, or otherwise improvechannel stability. The long-term impact of rigid structures on natural streamprocesses is relatively unknown. The objective of this study was to use long-termalluvial channel modeling to evaluate the effect of rigid structures on channelprocesses and assess current and future stream channel stability. The study wasconducted on Oliver Run, a small stream in Pennsylvania relocated due to highwayconstruction. Field data was collected along the 107 m reach to characterize thestream and provide model input, calibration, and verification data. FLUVIAL-12 wasused to evaluate the long-term impacts of rigid structures on natural channeladjustment, overall channel stability, and changing form and processes. Resultsindicated that the presence of rigid structures reduced channel width-to-depth ratios,minimized bed elevation changes due to short-term local scour and fill and long-termaggradation and degradation, limited lateral channel migration, promoted pool filling,and increased the mean bed material particle size throughout the reach. Results alsoshowed how alluvial channel modeling can be used to improve the stream restorationdesign effort.
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