Background

River2D is a two dimensional depth averaged finite element hydrodynamic model that has been customized for fish habitat evaluation studies. The River2D model suite actually consists of four programs: R2D_Bed , R2D_Ice, R2D_Mesh and River2D. All three programs have graphical user interfaces that are supported by any 32 bit version of Windows. R2D_Bed, R2D_Ice, and R2D_Mesh are graphical file editors. R2D_Bed was designed for editing bed topography data while R2D_Ice is intended for developing ice topographies to be used in the modelling of ice-covered domains. The R2D_Mesh program is used for the development of computational meshes that will ultimately be input for River2D.

These programs are typically used in succession. The normal modelling process would involve creating a preliminary bed topography file (text) from the raw field data, then editing and refining it using R2D_Bed. If an ice-covered domain were being modelled, R2D_Ice would be used to develop ice topography. The resulting bed topography file is used (inconjunction with an ice topography file where relevant) in R2D_Mesh to develop a computational discretization as input to River2D. River2D is then used to solve for the water depths and velocities throughout the discretization. Finally, River2D is used to visualize and interpret the results and perform PHABSIM type fish habitat analyses. An iterative approach at various stages, including modification of the bed topography (and ice topography), is usual.

R2D_Bed

Accurate representation of the physical features of the river channel bed is probably the most crucial factor in successful river flow modelling. In addition to accurate and extensive field data, judgement and experience are necessary to connect the scattered data points into a digital surface representation. The River2D model family is based on the Triangulated Irregular Network (TIN) methodology, including breaklines, for spatial interpolation of nodal parameters. The nodal values are usually measured points, but the breakline locations are judgemental. R2D_Bed allows interactive setting and deleting of breakline segments.

The relevant physical characteristics of the channel bed necessary for flow modelling are the bed elevation and the bed roughness height. R2D_Bed allows these values to be edited on an individual point basis or over irregular polygonal regions. R2D_Bed is also useful for editing channel index files, used in habitat analyses, with channel index replacing roughness height as the second nodal parameter.

R2D_Ice

The River2D is equipped to model flow under an ice cover of known geometry. Ice properties relevant to the 2D hydrodynamic calculations are ice thickness and ice roughness height at every node in the computational domain. R2D_Ice allows provides the user with an effective graphical environment for the development of ice topography files. Various commands allow the user to modify ice properties globally, regionally, or individually. Breakline can be inserted into an ice topography to define the edge of the ice in partially ice-covered domains.

R2D_Mesh

The purpose of R2D_Mesh is to provide a relatively easy to use but effective computational mesh generating environment for two-dimensional depth average finite element hydrodynamic modelling. To generate a mesh, the necessary input to the R2D_Mesh program is a bed topography file, possibly edited in R2D_Bed, defining the reach of interest using pointwise elevations and roughnesses. The points can be independent or connected in breaklines or featurelines. Once the bed topography is input, the user can graphically define the computation discretization and boundary conditions with the aid of various tools in the R2D_Mesh enviroment. When the user is satisfied, an input file for the River2D program can be generated.

River2D

The River2D model is a two-dimensional, depth averaged finite element model. It is intended for use on natural streams and rivers and has special features for accommodating supercritical /subcritical flow transitions and variable wetted area. It is basically a transient model but provides for an accelerated convergence to steady-state conditions.

The River2D environment has a number of options to aid the user in visualizing the progression and/or final results of the hydrodynamic computations including colour maps, contour maps and velocity vector fields.

The fish habitat module in River2D is based on the PHABSIM weighted usable area approach, adapted for a triangular irregular network geometrical description. The visual aids can also be used to display the results of habitat analyses.

In River2D, the user also has access to a few mesh editing commands so that adjustments can be made to the mesh without having to leave the River2D environment.

 

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