Rismo2D is a hydrodynamic numerical computer program to solve for the
depth-averaged shallow water equations by means of the Finite Element
Method. Rismo2D was developed during a research project funded by the
German Research Foundation (DFG) at the Institute of Hydraulic Enginee-
ring and Water Resources Management - Aachen University:

    The development of a numerical computational method
                for near-natural streams
                DFG-Project Ro 365 / 31

Rismo2D computes the water elevation and the depth-averaged velocity
for stationary or instationary streams. Based on a Finite Element
discretization the computation can be carried out for arbitrary water-
courses with complex geometrical and hydraulical boundary conditions.

Different laws may be used to account for bottom roughness. The friction
of submerged and non-submerged flood plain vegetation may be computed
by means of geometrical parameters.

The approximation of the (turbulent) Reynolds stresses is based on
Boussinesqs principle of eddy viscosity, where the eddy viscosity may
be computed with different closure models:

    constant elementwise eddy viscosity predefined by the user
    algebraic shear stress model (anisotropic / Elder)
    Prandtl's mixing layer model
    k-e-turbulence model

Furthermore, a Horizontal Large Eddy Simulation (H-LES) based on the
Smagorinsky model approach has been proved in some recent project
studies. Within the H-LES subgrid turbulence model both horizontal
velocity gradients (Prandtl's mixing length model) and bottom shear
stresses (Elder model) are taken into account.

After the solution of the flow field in one time step, the conservative
transport of matter in solution or suspension may be computed decoupled
by solving the depth-averaged advection diffusion equation. Also, the
transport of sediment as bed load may be computed based on the formulas
of Meyer-Peter-Mueller or van-Rijn. The computation of transport pro-
cesses is within the stage of development, and limited to one-fractional
transport. Bottom elevation changes are computed from the Exner equation
and incorporated within the next time step.

Michael Schroeder
25. April 2014