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[1] A depth-averaged two-dimensional numerical model has been developed to simulate flow, sediment transport, and bed topography in river channels with emergent and submerged rigid vegetation and large woody debris. The effect of helical flow in bends is considered by adopting an algebraic model for the dispersion terms in the depth-averaged two-dimensional momentum and suspended-sediment transport equations and by adjusting the bed load transport angle. The governing equations are discretized using the finite volume method on a nonstaggered, curvilinear grid. Model validity has been assessed using experimental data observed in both fixed-and movable-bed laboratory flumes and a natural channel with submerged and emergent rigid vegetation. In general, mean flow velocities, sediment transport rates, and changes in bed topography predicted by the model agree well with the experimental observations. For laboratory and field cases, root-mean-square relative errors for velocities were less than about 13% and 44%, respectively, and about 50% of errors for changes in bed topography were less than 14.5% and 8% of the flow depth, respectively.

River restoration and bank stabilization programs often use vegetation for improving stream corridor habitat, aesthetic and function. Yet no study has examined the use of managed vegetation plantings to transform a straight, degraded stream corridor into an ecologically functional meandering channel. Experimental data collected using a distorted Froude-scaled flume analysis show that channel expansion and widening, thalweg meandering and riffle and pool development are possible using discrete plantings of rigid, emergent vegetation, and the magnitudes of these adjustments depend on the shape of the vegetation zone and the density of the vegetation. These experimental results were verified and validated using a recently developed numerical model, and model output was then used to discuss mechanistically how rivers respond to the introduction of in-stream woody vegetation. Finally, a hybrid method of meander design is proposed herein where managed vegetation plantings are used to trigger or force the desired morphologic response, transforming a straight, degraded reach into a more functional meandering corridor. It is envisioned that such numerical models could become the primary tool for designing future stream restoration programs involving vegetation and assessing the long-term stability of such activities. Wu et al. (2005) developed a depth-averaged, two-dimensional numerical model to simulate flow, sediment transport and bed topography in mildly sinuous river channels with vegetation of various types. This model is based on the depth-integrated, Reynolds-averaged Navier-Stokes equations for shallow water flows as described by Wu and Wang (2004a, 2004b).Although the model described by Wu et al. (2005) is applicable to a wide range of hydraulic and geomorphic conditions with bedload and suspended load transport of sediment mixtures and with various configurations and types 894 S. J. Bennett et al.These effects can be seen from the topographic maps for the rectangular vegetation zone (Figure 3). Marked channel expansion occurs downstream and opposite the introduced vegetation zone in the form of bank toe erosion and bank failure (Figure 3(c)). Since flow stage is just below the threshold of sediment motion, this eroded and failed bank material is quickly deposited within the lower confines of the channel, and a migrating aggradational front is present in the mid-channel region upstream of the vegetation zone (see spatial coordinate x = 200 mm and y = 275 mm, herein denoted as [200,275], Figure 3(c)). As vegetation density increases, the magnitudes of bank erosion, channel widening and mid-channel aggradation increase. The greatest amount of bank erosion and channel widening occurs directly opposite and just downstream of the trailing edge of the vegetation zone. Given enough time, these zones of Figure 3. Contour maps of the measured bed surface topography for the rectangular vegetation zone with densities of (a) 0·77, (b) 2·94 and (c) 11·53 m −1 after run times listed in Table II. Flow is left to right. This fi...

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