COSFLOW: A Finite Element Model Coupling One-Dimensional Canal, Two-Dimensional Overland, and Three-Dimensional Subsurface Flow

Abstract : This report presents the user's manual of COSFLOW, which is a three-dimensional Finite Element Model coupling one-dimensional (1-D) Canal, two-dimensional (2-D) Overland, and three-dimensional (3-D) Subsurface Flow. The 1-D channel flow is described by water budget under the assumption that equilibrium within each channel reach is achieved instantaneously. The 2-D overland flow is modeled with a diffusive wave approach. Retention ponds included in the overland flow are simulated with a water budget approximation. In this version, solute transport is not considered in the coupled system; but for the future consideration, the subsurface solute transport module is included in the computer code. In this report, however, emphasis is given to the coupling of flow between 3-D subsurface, 1-D channel, and 2-D overland retention pond systems. The details associated with solute transport in the subsurface, such as density-dependent transport and salt intrusion, can be found in the user's manual of 3DFEMFAT. In the channel module, the volumetric flow rates from the channel to the subsurface nodes, or vice versa, are computed within each channel time-step, and are accumulated within each subsurface time-step (one subsurface time-step usually includes many channel time-steps). The pumping from the channel can be directed to another channel reach, a subsurface node, or a retention pond, which is designed to store excess water in a canal.