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r3.gwflow.1grass

NAME

r3.gwflow - Numerical calculation program for transient, confined groundwater flow in three dimensions

KEYWORDS

raster3d, voxel

SYNOPSIS

r3.gwflow
r3.gwflow help
r3.gwflow [-ms] phead=string status=string hc_x=string hc_y=string hc_z=string [q=string] s=string [r=string] output=string [velocity=string] dt=float [maxit=integer] [error=float] [solver=name] [relax=float] [--overwrite] [--verbose] [--quiet]

Flags:

-m

Use G3D mask (if exists)

-s

Use a sparse linear equation system, only available with iterative solvers

--overwrite

Allow output files to overwrite existing files

--verbose

Verbose module output

--quiet

Quiet module output

Parameters:

phead=string

The initial piezometric head in [m]

status=string

The status for each cell, = 0 - inactive, 1 - active, 2 - dirichlet

hc_x=string

The x-part of the hydraulic conductivity tensor in [m/s]

hc_y=string

The y-part of the hydraulic conductivity tensor in [m/s]

hc_z=string

The z-part of the hydraulic conductivity tensor in [m/s]

q=string

Sources and sinks in [m^3/s]

s=string

Specific yield in 1/m

r=string

Recharge raster map in m^3/s

output=string

The piezometric head result of the numerical calculation will be written to this map

velocity=string

Calculate the groundwater distance velocity vector field and write the x, y, and z components to maps named name_[xyz]. Name is basename for the new raster3d maps

dt=float

The calculation time in seconds
Default: 86400

maxit=integer

Maximum number of iteration used to solver the linear equation system
Default: 100000

error=float

Error break criteria for iterative solvers (jacobi, sor, cg or bicgstab)
Default: 0.0000000001

solver=name

The type of solver which should solve the symmetric linear equation system
Options: gauss,lu,cholesky,jacobi,sor,cg,bicgstab,pcg
Default: cg

relax=float

The relaxation parameter used by the jacobi and sor solver for speedup or stabilizing
Default: 1

DESCRIPTION

This numerical program calculates transient, confined groundwater flow in three dimensions based on volume maps and the current 3d region resolution. All initial- and boundary-conditions must be provided as volume maps.

This module calculates the piezometric head and optionally the groundwater velocity field. The vector components can be visualized with paraview if they are exported with r3.out.vtk.

The groundwater flow will always be calculated transient. If you want to calculate stady state, set the timestep to a large number (billions of seconds) or set the specific yield raster maps to zero.

NOTES

The groundwater flow calculation is based on Darcy's law and a finite volume discretization. The groundwater flow partial differential equation is of the following form:

(dh/dt)*S = Kxx * (d^2h/dx^2) + Kyy * (d^2h/dy^2) + Kzz * (d^2h/dz^2) + q

h -- the piezometric head im meters [m]

dt -- the time step for transient calculation in seconds [s]

S -- the specific yield [1/m]

b -- the bottom surface of the aquifer meters [m]

Kxx -- the hydraulic conductivity tensor part in x direction in meter per second [m/s]

Kyy -- the hydraulic conductivity tensor part in y direction in meter per seconds [m/s]

Kzz -- the hydraulic conductivity tensor part in z direction in meter per seconds [m/s]

q - inner source in [1/s]

Two different boundary conditions are implemented, the Dirichlet and Neumann conditions. By default the calculation area is surrounded by homogeneous Neumann boundary conditions. The calculation and boundary status of single cells can be set with the status map, the following cell states are supportet:

0 == inactive - the cell with status 0 will not be calulated, active cells will have a no flow boundary to an inactive cell

1 == active - this cell is used for groundwater calculation, inner sources can be defined for those cells

2 == Dirichlet - cells of this type will have a fixed piezometric head value which do not change over time

The groundwater flow equation can be solved with several solvers. Aditionally a direct Gauss solver and LU solver are available. Those direct solvers only work with quadratic matrices, so be careful using them with large maps (maps of size 10.000 cells will need more than one gigabyte of ram).

EXAMPLE

Use this small script to create a working groundwater flow area and data. Make sure you are not in a lat/lon projection.
# set the region accordingly
g.region res=25 res3=25 t=100 b=0 n=1000 s=0 w=0 e=1000

#now create the input raster maps for a confined aquifer
r3.mapcalc "phead=if(row() == 1 && depth() == 4, 50, 40)"
r3.mapcalc "status=if(row() == 1 && depth() == 4, 2, 1)"
r3.mapcalc "well=if(row() == 20 && col() == 20 , -0.00025, 0)"
r3.mapcalc "hydcond=0.00025"
r3.mapcalc "syield=0.0001"
r.mapcalc "recharge=0.0"

r3.gwflow --o -s solver=cg phead=phead status=status hc_x=hydcond hc_y=hydcond \
hc_z=hydcond q=well s=syield r=recharge output=gwresult dt=8640000 velocity=gwresult_velocity

# The data can be visulaized with paraview when exported with r3.out.vtk
r3.out.vtk -p in=gwresult,status vector=gwresult_velocity_x,gwresult_velocity_y,gwresult_velocity_z out=/tmp/gwdata3d.vtk

#now load the data into paraview

SEE ALSO

r.gwflow
r3.out.vtk

AUTHOR

Soeren Gebbert

Last changed: $Date: 2007-07-04 09:52:35 +0200 (mer, 04 lug 2007) $

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