r3.gwflow(1grass) GRASS GIS User's Manual r3.gwflow(1grass)
NAME
r3.gwflow - Numerical calculation program for transient, confined
groundwater flow in three dimensions.
KEYWORDS
raster3d, groundwater flow, voxel, hydrology
SYNOPSIS
r3.gwflow
r3.gwflow --help
r3.gwflow [-mf] phead=name status=name hc_x=name hc_y=name hc_z=name
[sink=name] yield=name [recharge=name] output=name [veloc-
ity_x=name] [velocity_y=name] [velocity_z=name] [budget=name]
dtime=float [maxit=integer] [error=float] [solver=name] [--over-
write] [--help] [--verbose] [--quiet] [--ui]
Flags:
-m
Use 3D raster mask (if exists)
-f
Use a full filled quadratic linear equation system, default is a
sparse linear equation system.
--overwrite
Allow output files to overwrite existing files
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog
Parameters:
phead=name [required]
Input 3D raster map with initial piezometric heads in [m]
status=name [required]
Input 3D raster map providing the status for each cell, = 0 - inac-
tive, 1 - active, 2 - dirichlet
hc_x=name [required]
Input 3D raster map with the x-part of the hydraulic conductivity
tensor in [m/s]
hc_y=name [required]
Input 3D raster map with the y-part of the hydraulic conductivity
tensor in [m/s]
hc_z=name [required]
Input 3D raster map with the z-part of the hydraulic conductivity
tensor in [m/s]
sink=name
Input 3D raster map with sources and sinks in [m^3/s]
yield=name [required]
Specific yield [1/m] input 3D raster map
recharge=name
Recharge input 3D raster map in m^3/s
output=name [required]
Output 3D raster map storing the piezometric head result of the nu-
merical calculation
velocity_x=name
Output 3D raster map storing the groundwater filter velocity vector
part in x direction [m/s]
velocity_y=name
Output 3D raster map storing the groundwater filter velocity vector
part in y direction [m/s]
velocity_z=name
Output 3D raster map storing the groundwater filter velocity vector
part in z direction [m/s]
budget=name
Output 3D raster map storing the groundwater budget for each cell
[m^3/s]
dtime=float [required]
The calculation time in seconds
Default: 86400
maxit=integer
Maximum number of iteration used to solve the linear equation sys-
tem
Default: 10000
error=float
Error break criteria for iterative solver
Default: 0.000001
solver=name
The type of solver which should solve the symmetric linear equation
system
Options: cg, pcg, cholesky
Default: cg
DESCRIPTION
This numerical module calculates implicit transient and steady state,
confined groundwater flow in three dimensions based on volume maps and
the current 3D region settings. All initial- and boundary-conditions
must be provided as volume maps. The unit in the location must be me-
ters.
This module is sensitive to mask settings. All cells which are outside
the mask are ignored and handled as no flow boundaries.
The module calculates the piezometric head and optionally the water
balance for each cell and the groundwater velocity field in 3 dimen-
sions. The vector components can be visualized with ParaView if they
are exported with r3.out.vtk.
The groundwater flow will always be calculated transient. For steady
state computation the user should set the timestep to a large number
(billions of seconds) or set the specific yield raster map to zero.
NOTES
The groundwater flow calculation is based on Darcy’s law and a numeri-
cal implicit finite volume discretization. The discretization results
in a symmetric and positive definite linear equation system in form of
Ax = b, which must be solved. The groundwater flow partial differential
equation is of the following form:
(dh/dt)*S = div (K grad h) + q
In detail for 3 dimensions:
(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/sinc 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 supported:
• 0 == inactive - the cell with status 0 will not be calculated,
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 piezomet-
ric head value which do not change over time
Note that all required raster maps are read into main memory. Addition-
ally the linear equation system will be allocated, so the memory con-
sumption of this module rapidely grow with the size of the input maps.
The resulting linear equation system Ax = b can be solved with several
solvers. An iterative solvers with sparse and quadratic matrices sup-
port is implemented. The conjugate gradients method with (pcg) and
without (cg) precondition. Additionally a direct Cholesky solver is
available. This direct solver only work with normal quadratic matrices,
so be careful using them with large maps (maps of size 10.000 cells
will need more than one Gigabyte of RAM). The user should always prefer
to use a sparse matrix solver.
EXAMPLE 1
This small script creates a working groundwater flow area and data. It
cannot be run in a lat/lon location.
# set the region accordingly
g.region res=25 res3=25 t=100 b=0 n=1000 s=0 w=0 e=1000 -p3
#now create the input raster maps for a confined aquifer
r3.mapcalc expression="phead = if(row() == 1 && depth() == 4, 50, 40)"
r3.mapcalc expression="status = if(row() == 1 && depth() == 4, 2, 1)"
r3.mapcalc expression="well = if(row() == 20 && col() == 20 && depth() == 2, -0.25, 0)"
r3.mapcalc expression="hydcond = 0.00025"
r3.mapcalc expression="syield = 0.0001"
r.mapcalc expression="recharge = 0.0"
r3.gwflow solver=cg phead=phead statuyield=status hc_x=hydcond hc_y=hydcond \
hc_z=hydcond sink=well yield=syield r=recharge output=gwresult dt=8640000 vx=vx vy=vy vz=vz budget=budget
# The data can be visualized with ParaView when exported with r3.out.vtk
r3.out.vtk -p in=gwresult,status,budget vector=vx,vy,vz out=/tmp/gwdata3d.vtk
#now load the data into ParaView
paraview --data=/tmp/gwdata3d.vtk
EXAMPLE 2
This will create a nice 3D model with geological layer with different
hydraulic conductivities. Make sure you are not in a lat/lon projec-
tion.
# set the region accordingly
g.region res=15 res3=15 t=500 b=0 n=1000 s=0 w=0 e=1000
#now create the input raster maps for a confined aquifer
r3.mapcalc expression="phead = if(col() == 1 && depth() == 33, 50, 40)"
r3.mapcalc expression="status = if(col() == 1 && depth() == 33, 2, 1)"
r3.mapcalc expression="well = if(row() == 20 && col() == 20 && depth() == 3, -0.25, 0)"
r3.mapcalc expression="well = if(row() == 50 && col() == 50 && depth() == 3, -0.25, well)"
r3.mapcalc expression="hydcond = 0.0025"
r3.mapcalc expression="hydcond = if(depth() < 30 && depth() > 23 && col() < 60, 0.000025, hydcond)"
r3.mapcalc expression="hydcond = if(depth() < 20 && depth() > 13 && col() > 7, 0.000025, hydcond)"
r3.mapcalc expression="hydcond = if(depth() < 10 && depth() > 7 && col() < 60, 0.000025, hydcond)"
r3.mapcalc expression="syield = 0.0001"
r3.gwflow solver=cg phead=phead statuyield=status hc_x=hydcond hc_y=hydcond \
hc_z=hydcond sink=well yield=syield output=gwresult dt=8640000 vx=vx vy=vy vz=vz budget=budget
# The data can be visualized with paraview when exported with r3.out.vtk
r3.out.vtk -p in=gwresult,status,budget,hydcond,well vector=vx,vy,vz out=/tmp/gwdata3d.vtk
#now load the data into paraview
paraview --data=/tmp/gwdata3d.vtk
SEE ALSO
r.gwflow, r.solute.transport, r3.out.vtk
AUTHOR
Sören Gebbert
This work is based on the Diploma Thesis of Sören Gebbert available
here at Technical University Berlin, Germany.
SOURCE CODE
Available at: r3.gwflow source code (history)
Accessed: unknown
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