The document discusses the capabilities of HEC-RAS for two-dimensional flow modeling, highlighting features such as the ability to perform 1D, 2D, or combined modeling, and the use of an implicit finite volume algorithm for the 2D equation solver. It details the software's support for structured and unstructured computational meshes, as well as its pre-processing of terrain to create hydraulic property tables. Additionally, the document mentions the integration of flooding animations using RAS Mapper and the software's compatibility with multi-processor systems.

2. HEC-RAS Two Dimensional Flow Modeling
Capabilities/Advantages
1. The ability to perform 1D, 2D only, or Combined 1D and 2D modeling
2. The 2D equation solver uses an Implicit Finite Volume algorithm.
3. Can solve either 2D Diffusion Wave or 2D Full Saint Venant Eqns.
4. The 1D and 2D solution algorithms are tightly coupled on a time step by time step
basis (or even iteration by iteration).
5. The software was designed to use Unstructured or Structured Computational
Meshes. The outer boundary of the computational mesh is defined with a multi-
point polygon.
6. The underlying terrain and the computational mesh are pre-processed in order to
develop detailed Hydraulic Property Tables for the Cells and the Cell Faces.
7. Mapping of the combined 1D/2D inundation area, and animations of the flooding
can be done right inside of RAS, using RAS-Mapper.
8. The 2D flow computations take advantage of Multi-processors
9. 64 Bit and 32 Bit Computational Engines.
2

3. 2D Hydraulics
• Shallow Water Equations
 Mass Conservation (Continuity)
 Momentum Equation:
 Gravity and Friction
 Hydrostatic pressure
 Acceleration (local and convective)
 Turbulence Modeling - Eddy viscosity (optional)
 Wind Forces (optional)
 Mud and Debris flows (optional)
 Earths Rotation - Coriolis term (optional)
• Diffusion Wave Equations
 Mass Conservation (Continuity)
 Momentum Equation:
 Gravity and Friction
 Hydrostatic pressure
3