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Two-dimensional habitat modeling is becoming more and more necessary because the eco-hydraulic information in longitudinal and lateral dimensions in rivers and wetlands is essential for habitat evaluation, especially in habitat restoration projects. A general habitat module based on the FVM-based CCHE2D model has been developed to reproduce and quantify the complex characteristics of flow in a river reach for better assessment of habitat. The established model has been applied to study the effect of large wood structures on fish habitat in the Little Topashaw Creek and the effect of sediment transport on fish habitat in a reach in the Mississippi River. Generally, the change of bed topography due to the addition of large wood structures can redistribute the water depth and flow velocity, which influence the distribution of habitat area. The usable habitat area is underestimated if vegetation is not considered, while it may be overestimated if sediment transport is not considered.

Results of two-dimensional (depth averaged) and three dimensional computations of a 1750m reach of the Sacramento River are compared with velocity data obtained in a large-scale, distorted physical model of the same reach. The aim was to predict the level of modeling required to predict the occurrence of bank erosion observed in the field. Further results are presented which show the outcome of deploying 5 groins to inhibit bank erosion upstream of a bridge abutment. The simulations are also compared with experimental data to assess the performance of alternative shear formulae. Truncation errors are estimated using two alternative techniques. The results suggest that the occurrence and mitigation of bank erosion in large natural river systems can be predicted to an acceptable degree of accuracy.

A willow post system is a type of bioengineering system used to reduce streambank erosion. In essence, a willow post system is a collection of rigid cylinders placed along a streambank. Herein, an analytical model that was developed to evaluate the hydrodynamics of newly constructed willow post systems is reviewed. The model is founded on wake theory and was originally developed for predicting depth-averaged velocities in straight trapezoidal channels with unsubmerged rigid cylinders. The model was recently modified and now includes a parameter for evaluating submerged vegetation and is referred to as the submergence ratio. Observed depth-averaged velocities from a physical model study are compared to predicted depth-averaged velocities from the original and the modified version of the analytical model. A comparison of coefficient of determination (r 2 ) values shows that the submergence ratio significantly improves the accuracy of predicted velocities in channels with submerged and unsubmerged vegetation.

Using dimensional analysis and experimental data from three previous studies, two relationships for predicting depth-averaged velocity distributions in straight trapezoidal channels were developed. The data had a range of discharges (8.0 to 4,248 l/s), velocities (0.10 to 1.03 m/s), bottom widths (0.30 to 3.6 m), flow depths (5.2 to 80.5 cm), and sideslopes (1.0 to 3.0, horiz./vert.). The first relationship is general and requires measured velocity data for calibration. When measured data are not available, the second model, for which specific coefficients are prescribed, must be used. The first model is more accurate and should be used when possible. The second model also yield s acceptable results. Among other things, the models can be employed in stable channel designs, streambank stability analyses, and to evaluate streambank stabilization designs including riprap and bioengineering designs. Brief reviews of the models are presented along with a demonstration application.

Two years of daily time exposure video images were analysed to examine the effect of incident wave conditions on the spacing and persistence of rip channels along a swell dominated, microtidal beach (Palm Beach, Sydney, Australia). The results indicated that rip channels do not have any preferred locations along the beach. Rip spacing did not increase or decrease with likewise variations in wave height. Once formed, rip channels migrated longshore under obliquely incident waves, while they were fixed in location under normal wave incidence. Gradients in longshore sediment transport caused by longshore currents due to obliquely incident waves appear to govern longshore migration of rip channels. A two-dimensional depth averaged hydrodynamic model (2DBEACH) was applied to idealised bathymetry to examine processes governing rip strength. The model results indicated that both rip velocity and transport increased with increasing wave height. Rip velocity also increased with falling tide levels, while rip transport initially increased and then decreased with falling tide levels. Centre for Natural Resources, Dept. of Land & Water Conservation, PO Box 2185, Dangar, NSW 2309, Australia. Phone: +61 2 4960 5033; E-mail: rranasinghe@dlwc.nsw.gov.au 2 School of Geography & Oceanography, Australian Defence Force Academy, Canberra, ACT 2600, Australia. E-mail: Graham.Symonds@adfa.edu.au 3 Department of Earth Sciences, University of Waikato, PB 3105, Hamilton, New Zealand. Email: kblack@ mailserv.waikato.ac.nz 4 College of Atmospheric and Oceanic Sciences, Oregon State University, 104 Ocean admin building, Corvallis, Oregon 97331-5503, USA. E-mail: holman@oce.orst.edu