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Modeling Surface and Groundwater Flow with FLO-2D

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Modeling Surface and Groundwater Flow with FLO-2D

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    1. Modeling Surface and Groundwater Flow with FLO-2D / MODFLOW Integration Reinaldo Garcia FLO-2D Software, Inc. May, 2009

    2. Outline MODFLOW Model link options Time-step syncronization Data input using GDS Applications

    3. MODFLOW U.S.G.S. MODULAR GROUND-WATER MODEL Finite difference layered 3D model

    4. Model Link Options Challenge: Synchronize time stepping between the two models. Two-way exchange of flow. MODFLOW uses stress periods and time steps. FLO-2D uses variable time steps

    5. MODFLOW 2005 All modifications done to the MODFLOW model were based on the model version code Version 1.4.00 updated last November 2007 and also known as MODFLOW 2005 (http://water.usgs.gov/nrp/gwsoftware/modflow2005/modflow2005.html)

    6. Models link The surface-subsurface water exchange is allowed to occur in any direction and is unsteady and spatially distributed. a particular time along the simulation, water may be infiltrating from the surface water to the groundwater while on other parts the opposite may be happening. the models are fully coupled and run simultaneously allowing modeling both groundwater recharge from surface water and river recharge from groundwater.

    7. Time step synchronization In MODFLOW the simulation is divided into a series of stress periods within which specified data (e.g. variable heads) are constant. Each stress period, in turn, is divided into a series of time steps. FLO-2D model works with variable time steps that are automatically adjusted internally based on stability criteria requirements. Because FLO-2D uses an explicit finite difference method to solve the surface water equations, usually its time step is much smaller than that defined for the MODFLOW model.

    8. Time-step synchronization

    10. Surface-subsurface water exchange The groundwater surface elevation is lower than the channel bed elevation, the computed infiltration volume is passed to the corresponding MODFLOW grid element. If there is no infiltration calculation in the FLO-2D channel component, the channel water surface elevation will be used to calculate the infiltration to MODFLOW element. If the groundwater head is higher than the channel water surface elevation, the flow will be toward the: QRIV = CRIV (HRIV – h(I,J,K)) Where: QRIV is the flow between the river and the aquifer HRIV is the water level (stage) in the stream or channel; CRIV is the hydraulic conductance of the stream-aquifer interconnection; and h(I,J,K) is the head at the grid element underlying the stream reach.  

    12. Data entry using GDS Writes a subset of MODFLO-2005 data files: Name File, Discretization File, Basic Package File, Time-Variant Specified-Head File, and Block-Centered Flow Package File. Allows creation of layers (confined and unconfined), stress periods (steady state and transient), and time-variant groundwater head cells.

    13. Data entry using GDS Manages the grid system to incorporate data layers, stress periods, and head cells. Allows defining top and bottom elevations of each layer of the groundwater model. Editing of MODFLO-2005 variables for the files listed above. Runs FLO-2D and MODFLOW-2005 as integrated models.

    18. FLO-2D MODFLOW model to simulate flooding, flow through hydraulic structures, and groundwater flow on the Avon Park Air Force Range (APAFR), FL.

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