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r.gwflow

Numerical calculation program for transient, confined and unconfined groundwater flow in two dimensions.

r.gwflow [-f] phead=name status=name hc_x=name hc_y=name [q=name] s=name [recharge=name] top=name bottom=name output=name [vx=name] [vy=name] [budget=name] type=string [river_bed=name] [river_head=name] [river_leak=name] [drain_bed=name] [drain_leak=name] dtime=float [maxit=integer] [maxit=integer] [error=float] [solver=name] [--overwrite] [--verbose] [--quiet] [--qq] [--ui]

Example:

r.gwflow phead=name status=name hc_x=name hc_y=name s=name top=name bottom=name output=name type=confined dtime=86400

grass.script.run_command("r.gwflow", phead, status, hc_x, hc_y, q=None, s, recharge=None, top, bottom, output, vx=None, vy=None, budget=None, type="confined", river_bed=None, river_head=None, river_leak=None, drain_bed=None, drain_leak=None, dtime=86400, maxit=10000, maxit=25, error=0.000001, solver="cg", flags=None, overwrite=False, verbose=False, quiet=False, superquiet=False)

Example:

gs.run_command("r.gwflow", phead="name", status="name", hc_x="name", hc_y="name", s="name", top="name", bottom="name", output="name", type="confined", dtime=86400)

Parameters

phead=name [required]
    Name of input raster map with initial piezometric head in [m]
status=name [required]
    Name of input raster map providing boundary condition status: 0-inactive, 1-active, 2-dirichlet
hc_x=name [required]
    Name of input raster map with x-part of the hydraulic conductivity tensor in [m/s]
hc_y=name [required]
    Name of input raster map with y-part of the hydraulic conductivity tensor in [m/s]
q=name
    Name of input raster map with water sources and sinks in [m^3/s]
s=name [required]
    Name of input raster map with storativity for confined or effective porosity for unconfined groundwater flow booth in [-]
recharge=name
    Recharge input raster map e.g: 6*10^-9 per cell in [m^3/s*m^2]
top=name [required]
    Name of input raster map describing the top surface of the aquifer in [m]
bottom=name [required]
    Name of input raster map describing the bottom surface of the aquifer in [m]
output=name [required]
    Output raster map storing the numerical result [m]
vx=name
    Output raster map to store the groundwater filter velocity vector part in x direction [m/s]
vy=name
    Output raster map to store the groundwater filter velocity vector part in y direction [m/s]
budget=name
    Output raster map to store the groundwater budget for each cell [m^3/s]
type=string [required]
    The type of groundwater flow
    Allowed values: confined, unconfined
    Default: confined
river_bed=name
    Name of input raster map providing the height of the river bed in [m]
river_head=name
    Name of input raster map providing the water level (head) of the river with leakage connection in [m]
river_leak=name
    Name of input raster map providing the leakage coefficient of the river bed in [1/s].
drain_bed=name
    Name of input raster map providing the height of the drainage bed in [m]
drain_leak=name
    Name of input raster map providing the leakage coefficient of the drainage bed in [1/s]
dtime=float [required]
    The calculation time in seconds
    Default: 86400
maxit=integer
    Maximum number of iteration used to solve the linear equation system
    Default: 10000
maxit=integer
    The maximum number of iterations in the linearization approach
    Default: 25
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
    Allowed values: cg, pcg, cholesky
    Default: cg
-f
    Allocate a full 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
--qq
    Very quiet module output
--ui
    Force launching GUI dialog

phead : str, required
    Name of input raster map with initial piezometric head in [m]
    Used as: input, raster, name
status : str, required
    Name of input raster map providing boundary condition status: 0-inactive, 1-active, 2-dirichlet
    Used as: input, raster, name
hc_x : str, required
    Name of input raster map with x-part of the hydraulic conductivity tensor in [m/s]
    Used as: input, raster, name
hc_y : str, required
    Name of input raster map with y-part of the hydraulic conductivity tensor in [m/s]
    Used as: input, raster, name
q : str, optional
    Name of input raster map with water sources and sinks in [m^3/s]
    Used as: input, raster, name
s : str, required
    Name of input raster map with storativity for confined or effective porosity for unconfined groundwater flow booth in [-]
    Used as: input, raster, name
recharge : str, optional
    Recharge input raster map e.g: 6*10^-9 per cell in [m^3/s*m^2]
    Used as: input, raster, name
top : str, required
    Name of input raster map describing the top surface of the aquifer in [m]
    Used as: input, raster, name
bottom : str, required
    Name of input raster map describing the bottom surface of the aquifer in [m]
    Used as: input, raster, name
output : str, required
    Output raster map storing the numerical result [m]
    Used as: output, raster, name
vx : str, optional
    Output raster map to store the groundwater filter velocity vector part in x direction [m/s]
    Used as: output, raster, name
vy : str, optional
    Output raster map to store the groundwater filter velocity vector part in y direction [m/s]
    Used as: output, raster, name
budget : str, optional
    Output raster map to store the groundwater budget for each cell [m^3/s]
    Used as: output, raster, name
type : str, required
    The type of groundwater flow
    Allowed values: confined, unconfined
    Default: confined
river_bed : str, optional
    Name of input raster map providing the height of the river bed in [m]
    Used as: input, raster, name
river_head : str, optional
    Name of input raster map providing the water level (head) of the river with leakage connection in [m]
    Used as: input, raster, name
river_leak : str, optional
    Name of input raster map providing the leakage coefficient of the river bed in [1/s].
    Used as: input, raster, name
drain_bed : str, optional
    Name of input raster map providing the height of the drainage bed in [m]
    Used as: input, raster, name
drain_leak : str, optional
    Name of input raster map providing the leakage coefficient of the drainage bed in [1/s]
    Used as: input, raster, name
dtime : float, required
    The calculation time in seconds
    Default: 86400
maxit : int, optional
    Maximum number of iteration used to solve the linear equation system
    Default: 10000
maxit : int, optional
    The maximum number of iterations in the linearization approach
    Default: 25
error : float, optional
    Error break criteria for iterative solver
    Default: 0.000001
solver : str, optional
    The type of solver which should solve the symmetric linear equation system
    Used as: name
    Allowed values: cg, pcg, cholesky
    Default: cg
flags : str, optional
    Allowed values: f
    f
        Allocate a full quadratic linear equation system, default is a sparse linear equation system.
overwrite: bool, optional
    Allow output files to overwrite existing files
    Default: False
verbose: bool, optional
    Verbose module output
    Default: False
quiet: bool, optional
    Quiet module output
    Default: False
superquiet: bool, optional
    Very quiet module output
    Default: False

DESCRIPTION

r.gwflow is a numerical program which calculates implicit transient, confined and unconfined groundwater flow in two dimensions based on raster maps and the current region settings. All initial and boundary conditions must be provided as raster maps. The unit of the current project's coordinate reference system must be meters.

This module is sensitive to mask settings. All cells which are outside the mask are ignored and handled as no flow boundaries.

Workflow of r.gwflow
Workflow of r.gwflow

r.gwflow calculates the piezometric head and optionally the water budget and the filter velocity field, based on the hydraulic conductivity and the piezometric head. The vector components can be visualized with paraview if they are exported with r.out.vtk.

The groundwater flow will always be calculated transient. For stady state computation set the timestep to a large number (billions of seconds) or set the storativity/ effective porosity raster map to zero.

The water budget is calculated for each non inactive cell. The sum of the budget for each non inactive cell must be near zero. This is an indicator of the quality of the numerical result.

NOTES

The groundwater flow calculation is based on Darcy's law and a numerical 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 2 dimensions:

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

  • h -- the piezometric head im [m]
  • dt -- the time step for transient calculation in [s]
  • S -- the specific storage [1/m]
  • Kxx -- the hydraulic conductivity tensor part in x direction in [m/s]
  • Kyy -- the hydraulic conductivity tensor part in y direction in [m/s]
  • q - inner source/sink in meter per second [1/s]

Confined and unconfined groundwater flow is supported. Be aware that the storativity input parameter is handled differently in case of unconfined flow. Instead of the storativity, the effective porosity is expected.

To compute unconfined groundwater flow, a simple Picard based linearization scheme is used to solve the resulting non-linear equation system.

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 must be set with a status map, the following states are supported:

  • 0 == inactive - the cell with status 0 will not be calculated, active cells will have a no flow boundary to this cell
  • 1 == active - this cell is used for groundwater flow calculation, inner sources and recharge can be defined for those cells
  • 2 == Dirichlet - cells of this type will have a fixed piezometric head value which do not change over the time

Note that all required raster maps are read into main memory. Additionally the linear equation system will be allocated, so the memory consumption 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 support 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). Always prefer a sparse matrix solver.

EXAMPLE

Use this small script to create a working groundwater flow area and data. Make sure you are not in a lat/lon projection. It includes drainage and river input as well.

# 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 confined and unconfined aquifers
r.mapcalc expression="phead = if(row() == 1 , 50, 40)"
r.mapcalc expression="status = if(row() == 1 , 2, 1)"
r.mapcalc expression="well = if(row() == 20 && col() == 20 , -0.01, 0)"
r.mapcalc expression="hydcond = 0.00025"
r.mapcalc expression="recharge = 0"
r.mapcalc expression="top_conf = 20.0"
r.mapcalc expression="top_unconf = 70.0"
r.mapcalc expression="bottom = 0.0"
r.mapcalc expression="null = 0.0"
r.mapcalc expression="poros = 0.15"
r.mapcalc expression="s = 0.0001"

# The maps of the river
r.mapcalc expression="river_bed = if(col() == 35 , 48, null())"
r.mapcalc expression="river_head = if(col() == 35 , 49, null())"
r.mapcalc expression="river_leak = if(col() == 35 , 0.0001, null())"

# The maps of the drainage
r.mapcalc expression="drain_bed = if(col() == 5 , 48, null())"
r.mapcalc expression="drain_leak = if(col() == 5 , 0.01, null())"

#confined groundwater flow with cg solver and sparse matrix, river and drain
#do not work with this confined aquifer (top == 20m)
r.gwflow solver=cg top=top_conf bottom=bottom phead=phead status=status \
  hc_x=hydcond hc_y=hydcond q=well s=s recharge=recharge output=gwresult_conf \
  dt=8640000 type=confined vx=gwresult_conf_velocity_x vy=gwresult_conf_velocity_y budget=budget_conf

#unconfined groundwater flow with cg solver and sparse matrix, river and drain are enabled
# We use the effective porosity as storativity parameter
r.gwflow solver=cg top=top_unconf bottom=bottom phead=phead \
  status=status hc_x=hydcond hc_y=hydcond q=well s=poros recharge=recharge \
  river_bed=river_bed river_head=river_head river_leak=river_leak \
  drain_bed=drain_bed drain_leak=drain_leak \
  output=gwresult_unconf dt=8640000 type=unconfined vx=gwresult_unconf_velocity_x \
  budget=budget_unconf vy=gwresult_unconf_velocity_y

# The data can be visulaized with paraview when exported with r.out.vtk
r.out.vtk -p in=gwresult_conf,status vector=gwresult_conf_velocity_x,gwresult_conf_velocity_y,null \
  out=/tmp/gwdata_conf2d.vtk
r.out.vtk -p elevation=gwresult_unconf in=gwresult_unconf,status vector=gwresult_unconf_velocity_x,gwresult_unconf_velocity_y,null \
  out=/tmp/gwdata_unconf2d.vtk

#now load the data into paraview
paraview --data=/tmp/gwdata_conf2d.vtk &
paraview --data=/tmp/gwdata_unconf2d.vtk &

SEE ALSO

r.solute.transport, r3.gwflow, r.out.vtk

AUTHOR

Sören Gebbert

This work is based on the Diploma Thesis of Sören Gebbert available here at Technical University Berlin in Germany.

SOURCE CODE

Available at: r.gwflow source code (history)
Latest change: Friday Mar 07 07:39:48 2025 in commit e1e37d8