Channel Configuration Control on Energy Dissipation
and Hydraulic Jump Regime at River Steps
Gregory B. Pasternack and Joshua R. Wyrick
Wyrick, J. R. and Pasternack, G. B. 2008. Modeling energy dissipation and hydraulic jump regime responses to channel nonuniformity at river steps. Journal of Geophysical Research 113, F03003, doi:10.1029/2007JF000873. (available upon request to either author)
The river step is an important driver for geomorphic evolution in bedrock rivers, but the effect that variations in channel geometry upstream and downstream of a river step have on hydraulic jump regime and energy dissipation has not previously been investigated.
The associated hydraulic jump is inherent to a river step and its regime is a primary control on step morphodynamics. In turn, the hydraulic jump regime is controlled by several variables as detailed in a new conceptual framework described by Wyrick and Pasternack (2008).
Wyrick and Pasternack (2008) described a new parsimonious semi-analytical numerical model of step hydraulics to quantify energy dissipation and delineate hydraulic jump regimes, accounting for discharge, jump submergence, and non-uniform channel geometry through a step. This model is called the Nonuniform Step Energy Analysis Model (NSEAM), version 1.0. Despite remaining limitations in step theory, NSEAM simulates how natural steps respond to a wide range of conditions. The model shows that hydraulic jump regime and energy dissipation exhibit greater sensitivity to channel non-uniformity as discharge increases and/or step height decreases. Also, channel conditions that create greater jump submergence lead to decreased energy dissipation, regardless of the discharge regime. The model also reinforces the common observation about gully erosion that downstream channel widening enhances upstream knickpoint migration. The new algorithm may be used to aid river engineering involving steps and could be useful for landscape evolution modeling.
NSEAM 1.0 is presently implemented in Mathematica and in Excel versions, but only the Excel version is polished for public distribution.
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