WIT Press

Downstream Hydraulic Geometry For Incised Channels


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WIT Press


N. A. Hadadin


The DEC Project data was used to develop several regression relationships for incised channels (CEM Type IV or V). The shape factor that was developed for downstream hydraulic geometry regression analysis of CEM Types IV and V incised channel data is ψ= 0.206 0.114 29.39 s S d − . The shape factor (W/d) is directly proportional to the bed material size and inversely proportional to the slope. The effect of discharge on the shape factor is negligible. The physical meaning of this equation is that small slopes and coarse grain sizes produce large width/depth ratios, and steep slopes and fine grain sizes produce small width/depth ratios. Two regression equations were developed for the hydraulic geometry for top width and mean depth with 95% upper and lower confidence interval for incised channels (CEM Types IV and V) in the DEC Project. There were minor differences between the exponents of flow discharge and channel slope between this study and the study of other investigators. Keywords: shape factor, incised channel, hydraulic geometry, flow discharge, width depth ratio. 1 Introduction Downstream hydraulic geometry deals with variation in a cross section along a stream, where cross-section form adjusts to accommodate the discharge and sediment load supplied from the drainage basin, within the additional constraints imposed by boundary composition, bank vegetation, and valley slope. A single channel-forming discharge is assumed to represent the channel morphology at a location, for various sites along the channel. Channel dimensions are not arbitrary but are adjusted, through the processes of erosion and deposition, to the quantity of water moving through the cross section so that the channel contains


shape factor, incised channel, hydraulic geometry, flow discharge, width depth ratio.