RiverFLO-2D

TWO-DIMENSIONAL FINITE-ELEMENT RIVER DYNAMICS MODEL

A.S.A.P. Modeling with RiverFLO-2D

Finite element mesh showing refinement around culvert crossing for a restoration project in the White River, WA, USA.

Advanced

RiverFLO-2D uses a state-of-the art finite element solution algorithm that solves most of the shortcomings of comparable models. The explicit time-stepping algorithm does not require solution of large matrix systems and provides flexibility for efficient parallelization.

Stable

RiverFLO-2D provides one of the fastest and more stable 2D finite element models commercially available for supercritical and subcritical flows. The computer code has been parallelized using OpenMP standard instructions providing considerable computer-time savings and taking advantage of multi-core computers (Duo/Quad) that use MS-Windows XP or Vista operating systems.

Accurate

RiverFLO-2D provides a mass conservative and robust dry-wet treatment method that allows to dry large mesh areas without generating artificial velocities or surging. The model reports on volume conservation allowing users to assess the model accuracy as the simulation progresses.

Productive

RiverFLO-2D minimizes time consuming model setup time letting you run more scenarios and concentrate in the actual model application and results analyses. RiverFLO-2D helps you be more productive allowing starting the simulation with the real initial conditions even if the whole river bed is dry.

detailed 2-D channel hydraulics and overbank flooding through the shorter project reach. RiverFLO-2D user interface is based upon Argus Open Numerical Environment (Argus ONE). This GIS-integrated software system provides interactive functions to generate and refine the finite element mesh. It also facilitates, assigning boundary conditions and

Model Applications

RiverFLO-2D can be applied to time-dependent and steady-state two-dimensional river simulations for either rigid bed or mobile bed applications. The model generates high resolution spatially variable results with a detailed depiction of the flow field. Typical model applications include:

Detailed in-channel river hydrodynamics;
River overbank flooding;
Levee removal;
Dam-break flood analysis;
Sediment transport – mobile bed;
Bank erosion protection design and analysis;
River restoration design.

Finite element mesh refined around Engineered Log Jams designed for a bank protection project in the Hoh River, WA, USA.

Model Formulation

Equations

RiverFLO-2D is based on the depth-averaged equations that govern free surface flow, sediment transport and bed evolution in rivers:

With the sediment transport module, users can select from six sediment transport capacity formulas for mobile bed applications, including, Meyer-Peter and Muller, Yang, Ackers-White, Karim-Kennedy, Toffaleti, and Wilcock-Crowe for gravel-bed rivers. Bed aggradation and degradation is tracked. As an example, RiverFLO-2D procedure based on the Meyer-Peter and Muller formulation uses the following equations:

Solution method

The Finite Element Method is the preferred numerical approach for detailed in-channel river analysis because the finite element mesh adapts to irregular channel geometry. The method is also supported by a solid mathematical foundation. RiverFLO-2D implements an efficient four-step explicit time-stepping scheme to solve the full dynamic wave momentum equations. RiverFLO-2D does not require adding artificial diffusion to stabilize the numerical solution. The spatial discretization uses triangular elements and since the solution method is explicit, it does not involve solution of large matrix systems. RiverFLO-2D has a robust mass (volume) conservative drying-wetting algorithm that permits portions of the mesh to become repetitively dry and wet during simulations. Some 2D channel models cannot simulate an initial dry river bed, and require a time-consuming mesh draining process until the actual dry bed conditions are reached. This is commonly known as model spin-down. In RiverFLO-2D, the river bed may be initially dry or it may become dry during the simulation and the model does not require the costly spin-down computational process.

Parallelization for multiple processor computers

RiverFLO-2D parallelized computer code, takes advantage of multi-core computers that use MS-Windows XP or Vista operating systems. Most 2D hydraulic models are either based on sequential codes that do not utilize multiple-threading programming techniques or have been parallelized in computer cluster environments that are often not accessible to many consulting engineering companies and government agencies. Tests in multi-core processor computers indicate that the RiverFLO-2D model is able to run up to 2.5 faster than the sequential code in single processor computers.

Verification

To verify RiverFLO-2D capabilities to simulate river hydrodynamics, the model has been tested following the procedures recommended by the ASCE 3D Flow Model Verification and Validation Committee. This validation process involved testing the model with analytical solutions and simplified cases, comparison against laboratory experiments and application to field scale projects with available data. RiverFLO-2D testing results have been published in peer-reviewed journals. Application to field scale problems, such as the well-known Malpasset dam-break event, reveals that the model accurately replicates wave travel times and measured water surface elevations on an initially dry river bed.