HR: 1330h
AN: H12B-0977    [PDF]
TI: MOD\_FreeSurf2D: a Surface Fluid Flow Simulation Model for Rivers, Streams, and Shallow Estuaries
AU: * Martin, N
EM: nmartin@pangea.stanford.edu
AF: Stanford University, Braun Hall, Bldg. 320 450 Serra Mall, Stanford, CA 94305-2115 United States
AU: Gorelick, S M
EM: gorelick@pangea.stanford.edu
AF: Stanford University, Braun Hall, Bldg. 320 450 Serra Mall, Stanford, CA 94305-2115 United States
AB: The MOD\_FreeSurf2D, Modular Free Surface Flow in Two-Dimensions, computer model simulates free surface fluid flow in streams, rivers, and shallow estuaries under the assumptions of a well-mixed water column, a small water depth to width ratio, and a hydrostatic pressure distribution. The dependent variables in the model are free surface elevation, which provides total water depth, and fluid velocity. Primary advantages of MOD\_FreeSurf2D relative to other two-dimensional models are a stable and computationally efficient numerical representation and a transparent representation of wetting and drying of the simulation domain. MOD\_FreeSurf2D approximates the depth-averaged, shallow water equations with a finite volume, semi-implicit, semi-Lagrangian numerical representation similar to the TRIM method (Casulli, 1990; Casulli and Cheng, 1992; Casulli, 1999). The semi-implicit, semi-Lagrangian approach is computationally efficient because time steps can exceed the Courant-Friedrich-Lewy (CFL) stability criterion without significant accuracy degradation (Robert, 1982; Casulli, 1990). The rectangular, Arakawa C-grid, finite-volume layout allows flooding and drying in response to changing flow conditions without prior channel specification or closed boundary specification. Open boundary conditions available in MOD\_FreeSurf2D are specified flux, specified total water depth, specified velocity, radiation free surface, and radiation velocity. MOD\_FreeSurf2D requires initial topography, undisturbed water depth, and Manning's roughness coefficient. MOD\_FreeSurf2D simulated results are shown to converge to the semi-empirical solution for a simple straight channel case. Two applications demonstrate the accuracy of MOD\_FreeSurf2D. The first application is the evolution of water depth in the dambreak-style flume experiment of Bellos et al. (1992). In this case, MOD\_FreeSurf2D accurately simulates the changing water depth in the flume during the experiment and models the wetting of the flume below the dam and the drying of the flume above the dam. The second application is simulation of a reach of the Kootenai River, ID studied by Lipscomb et al. (1998). Detailed 3D spatial measurements of water depth and velocity were numerically integrated and compared to the 2D values produced by MOD\_FreeSurf2D. Results indicate that MOD\_FreeSurf2D accurately simulates depth-averaged velocity and total water depth on the reach scale. Currently, MOD\_FreeSurf2D is a fully vectorized set of custom Matlab functions. References: Bellos, C.V., Soulis, J.V., and Sakkas, J.G., 1992, Experimental Investigation of Two-dimensional Dam-break Induced Flows, Journal of Hydraulic Research, v. 20, p. 47-63. Casulli, V., 1999, A Semi-Implicit Finite Difference Method for Non-Hydrostatic, Free-Surface Flows, International Journal for Numerical Methods in Fluids, v. 30, p. 425-440. Casulli, V., 1990, Semi-implicit Finite Difference Methods for the Two-Dimensional Shallow Water Equations, Journal of Computational Physics, v. 86, p. 56-74. Casulli, V. and Cheng, R.T., 1992, Semi-implicit Finite Difference Methods for Three-Dimensional Shallow Water Flow, International Journal for Numerical Methods in Fluids, v. 15, p. 629-648. Lipscomb, S.W., Berenbrock, C., and Doyle, J.D., 1997, Spatial Distribution of Stream Velocities for the Kootenai River Near Bonners Ferry, ID, June 1997. U.S. Geological Survey Open File Report 97-830, 174 p. Robert, A., 1982, A Semi-Lagrangian and Semi-Implicit Numerical Integration Scheme for the Primitive Meteorological Equations, Journal of the Meteorological Society of Japan, v.60, n. 1. p. 319-325.
DE: 1899 General or miscellaneous
SC: Hydrology [H]
MN: 2003 Fall Meeting