Visual Modflow.ppt 6q5f2n

Brief Introduction of

Visual MODFLOW

Introduction  Visual MODFLOW is the USGS's three-dimensional (3D)

finite-difference groundwater model that was first published in 1984.  Visual MODFLOW is the most complete, and -friendly,

modeling environment for practical applications in threedimensional groundwater flow and contaminant transport simulation.

Characteristics

 Widely used ground-water flow simulation program that

runs on any platform (Windows, Unix, Linux,…);  Open source (Anyone can check and change the source

code);  A modular structure that allows it to be easily modified to

adapt the code for a particular application (‘Processes’ and ‘Packages’).

Some modules

Programs based on MODFLOW – Public domain/open source • MT3DMS (multi-species solute or heat transport, some

reactions, dual porosity) (Chunmiao Zheng, U Alabama) • MODPATH (particle tracking) (Dave Pollock, USGS) • SEAWAT (density-dependent transport using MODFLOW

and MT3DMS) (Chris Langevin, USGS)… – Commercial • MODHMS-Surfact (Integrated sw/gw/unsat) • GUI’s: Visual MODFLOW, Groundwater Vistas, GMS,

PMWin, …

Governing Equations Confined Aquifer  h  h  h h (K x )  (K y )  (K z )  Ss W x x y y z z t

S s   g ( + n )

Unconfined Aquifer  h  h  h h ( Kx ) ( Ky )  ( Kz )  Sy W x x y y z z t

Conceptual model . A simplified representation of the physical hydrogeological setting. • • • • •

The geologic and hydrologic framework; Media type; Hydraulic properties; Sources and sinks of flow; …

(a)

(b)

Conceptual representation of leakage through a riverbed into a cell (a) (b)

Cross section of an unconfined aquifer containing a stream Conceptual representative of streamaquifer interconnection in simulation

Recharge, discharge, and runoff of groundwater

Input of Visual MODFLOW .1. Boundary Mathematical statements specifying the dependent variable (head) or the derivative of the dependent variable (flux) at the boundaries of the problem domain.

Input of Visual MODFLOW •

1) Specified head boundaries (Dirichlet conditions) for which head is given.

•

2) Specified flow boundaries (Neumann conditions) for which the derivative of head (flux) across the boundary is given. An no-flow boundary condition is set by specifying flux to be zero.

•

3) Head-dependent flow boundaries (Cauchy or mixed boundary conditions) for which flux across the boundary is calculated given a boundary value.

Boundary Setting in Visual MODFLOW • Constant Head

• Drain

• River

• Lake

• Stream

• Wall

• General Head

• Recharge

• Evaporation

• ……

Input of Visual MODFLOW .2. Source and sink “Among the many problems in heat-conduction analogous to those in ground-water hydraulics are those concerning sources and sinks, sources being analogous to recharging wells and sinks to ordinary discharging wells.” --- C.V. Theis, 1935

Input of Visual MODFLOW .3. Grid The Grid module allows the to define and discretize the modeling domain. The can add or delete gridlines, change cell or layer elevations, or remove cells from the computations.

Input of Visual MODFLOW .Other Input •

Wells

•

Properties

•

Particles(MODPATH)

•

Leakage

•

Zone budget

•

……

Output of Visual MODFLOW The output allows the to visualize, print, and export the simulation results. Five types of maps:

Four types of graphs:

• Calibration Residual Maps • Contour Maps • Pathline Maps • Velocity Vectors Maps • Zone Budget Maps

• Calibration Graphs • Time-Series Graphs • Mass Balance Graphs • Zone Budget Graphs

Some useful website

USGS Software website: http://water.usgs.gov/ogw/modflow/MODFLOW.html

http://water.usgs.gov/nrp/gwsoftware/ Online Visual MODFLOW manual: http://water.usgs.gov/nrp/gwsoftware/modflow2000/MFDOC/guide.html

Thank you for your attention!