## table of contents

r.solute.transport(1grass) | GRASS GIS User's Manual | r.solute.transport(1grass) |

# NAME¶

**r.solute.transport** - Numerical calculation program
for transient, confined and unconfined solute transport in two
dimensions

# KEYWORDS¶

raster, hydrology, solute transport

# SYNOPSIS¶

**r.solute.transport**

**r.solute.transport --help**

**r.solute.transport** [-**fc**] **c**=*name*
**phead**=*name* **hc_x**=*name* **hc_y**=*name*
**status**=*name* **diff_x**=*name*
**diff_y**=*name* [**q**=*name*] [**cin**=*name*]
**cs**=*name* **rd**=*name* **nf**=*name*
**top**=*name* **bottom**=*name* **output**=*name*
[**vx**=*name*] [**vy**=*name*] **dtime**=*float*
[**maxit**=*integer*] [**error**=*float*]
[**solver**=*name*] [**relax**=*float*]
[**al**=*float*] [**at**=*float*]
[**loops**=*float*] [**stab**=*string*] [--**overwrite**]
[--**help**] [--**verbose**] [--**quiet**] [--**ui**]

## Flags:¶

**-f**-

Use a full filled quadratic linear equation system, default is a sparse linear equation system. **-c**-

Use the Courant-Friedrichs-Lewy criteria for time step calculation **--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:¶

**c**=*name***[required]**-

The initial concentration in [kg/m^3] **phead**=*name***[required]**-

The piezometric head in [m] **hc_x**=*name***[required]**-

The x-part of the hydraulic conductivity tensor in [m/s] **hc_y**=*name***[required]**-

The y-part of the hydraulic conductivity tensor in [m/s] **status**=*name***[required]**-

The status for each cell, = 0 - inactive cell, 1 - active cell, 2 - dirichlet- and 3 - transfer boundary condition **diff_x**=*name***[required]**-

The x-part of the diffusion tensor in [m^2/s] **diff_y**=*name***[required]**-

The y-part of the diffusion tensor in [m^2/s] **q**=*name*-

Groundwater sources and sinks in [m^3/s] **cin**=*name*-

Concentration sources and sinks bounded to a water source or sink in [kg/s] **cs**=*name***[required]**-

Concentration of inner sources and inner sinks in [kg/s] (i.e. a chemical reaction) **rd**=*name***[required]**-

Retardation factor [-] **nf**=*name***[required]**-

Effective porosity [-] **top**=*name***[required]**-

Top surface of the aquifer in [m] **bottom**=*name***[required]**-

Bottom surface of the aquifer in [m] **output**=*name***[required]**-

The resulting concentration of the numerical solute transport calculation will be written to this map. [kg/m^3] **vx**=*name*-

Calculate and store the groundwater filter velocity vector part in x direction [m/s]

**vy**=*name*-

Calculate and store the groundwater filter velocity vector part in y direction [m/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* **error**=*float*-

Error break criteria for iterative solver

Default:*0.000001* **solver**=*name*-

The type of solver which should solve the linear equation system

Options:*gauss, lu, jacobi, sor, bicgstab*

Default:*bicgstab* **relax**=*float*-

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

Default:*1* **al**=*float*-

The longditudinal dispersivity length. [m]

Default:*0.0* **at**=*float*-

The transversal dispersivity length. [m]

Default:*0.0* **loops**=*float*-

Use this number of time loops if the CFL flag is off. The timestep will become dt/loops.

Default:*1* **stab**=*string*-

Set the flow stabilizing scheme (full or exponential upwinding).

Options:*full, exp*

Default:*full*

# DESCRIPTION¶

This numerical program calculates numerical implicit transient and
steady state solute transport in porous media in the saturated zone of an
aquifer. The computation is based on raster maps and the current region
settings. All initial- and boundary-conditions must be provided as raster
maps. The unit of the 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.

This module calculates the concentration of the solution and optional the
velocity field, based on the hydraulic conductivity, the effective porosity
and the initial piecometric heads. The vector components can be visualized
with paraview if they are exported with r.out.vtk.

Use r.gwflow to compute the piezometric heights of the aquifer. The
piezometric heights and the hydraulic conductivity are used to compute the
flow direction and the mean velocity of the groundwater. This is the base of
the solute transport computation.

The solute transport will always be calculated transient. For stady state
computation set the timestep to a large number (billions of seconds).

To reduce the numerical dispersion, which is a consequence of the convection
term and the finite volume discretization, you can use small time steps and
choose between full and exponential upwinding.

# NOTES¶

The solute transport calculation is based on a
diffusion/convection partial differential equation and a numerical implicit
finite volume discretization. Specific for this kind of differential
equation is the combination of a diffusion/dispersion term and a convection
term. The discretization results in an unsymmetric linear equation system in
form of *Ax = b*, which must be solved. The solute transport partial
differential equation is of the following form:

(dc/dt)*R = div ( D grad c - uc) + cs -q/nf(c - c_in)

- c -- the concentration [kg/m^3]
- u -- vector of mean groundwater flow velocity
- dt -- the time step for transient calculation in seconds [s]
- R -- the linear retardation coefficient [-]
- D -- the diffusion and dispersion tensor [m^2/s]
- cs -- inner concentration sources/sinks [kg/m^3]
- c_in -- the solute concentration of influent water [kg/m^3]
- q -- inner well sources/sinks [m^3/s]
- nf -- the effective porosity [-]

Three different boundary conditions are implemented, the Dirichlet, Transmission and Neumann conditions. The calculation and boundary status of single cells can be set with the 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 an inactive cell
- 1 == active - this cell is used for sloute transport calculation, inner sources can be defined for those cells
- 2 == Dirichlet - cells of this type will have a fixed concentration value which do not change over time
- 3 == Transmission - cells of this type should be placed on out-flow boundaries to assure the flow of the solute stream out

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. Several iterative solvers with unsymmetric sparse and quadratic matrices support are implemented. The jacobi method, the Gauss-Seidel method and the biconjugate gradients-stabilized (bicgstab) method. Additionally 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). Always prefer a sparse matrix solver.

# EXAMPLE¶

Use this small python script to create a working groundwater flow
/ solute transport area and data. Make sure you are not in a lat/lon
projection.

#!/usr/bin/env python3 # This is an example script how groundwater flow and solute transport are # computed within GRASS GIS import sys import os import grass.script as gs # Overwrite existing maps gs.run_command("g.gisenv", set="OVERWRITE=1") gs.message(_("Set the region")) # The area is 200m x 100m with a cell size of 1m x 1m gs.run_command("g.region", res=1, res3=1, t=10, b=0, n=100, s=0, w=0, e=200) gs.run_command("r.mapcalc", expression="phead = if(col() == 1 , 50, 40)") gs.run_command("r.mapcalc", expression="phead = if(col() ==200 , 45 + row()/40, phead)") gs.run_command("r.mapcalc", expression="status = if(col() == 1 || col() == 200 , 2, 1)") gs.run_command("r.mapcalc", expression="well = if((row() == 50 && col() == 175) || (row() == 10 && col() == 135) , -0.001, 0)") gs.run_command("r.mapcalc", expression="hydcond = 0.00005") gs.run_command("r.mapcalc", expression="recharge = 0") gs.run_command("r.mapcalc", expression="top_conf = 20") gs.run_command("r.mapcalc", expression="bottom = 0") gs.run_command("r.mapcalc", expression="poros = 0.17") gs.run_command("r.mapcalc", expression="syield = 0.0001") gs.run_command("r.mapcalc", expression="null = 0.0") gs.message(_("Compute a steady state groundwater flow")) gs.run_command("r.gwflow", solver="cg", top="top_conf", bottom="bottom", phead="phead",\

status="status", hc_x="hydcond", hc_y="hydcond", q="well", s="syield",\

recharge="recharge", output="gwresult_conf", dt=8640000000000, type="confined") gs.message(_("generate the transport data")) gs.run_command("r.mapcalc", expression="c = if(col() == 15 && row() == 75 , 500.0, 0.0)") gs.run_command("r.mapcalc", expression="cs = if(col() == 15 && row() == 75 , 0.0, 0.0)") gs.run_command("r.mapcalc", expression="tstatus = if(col() == 1 || col() == 200 , 3, 1)") gs.run_command("r.mapcalc", expression="diff = 0.0000001") gs.run_command("r.mapcalc", expression="R = 1.0") # Compute the initial state gs.run_command("r.solute.transport", solver="bicgstab", top="top_conf",\

bottom="bottom", phead="gwresult_conf", status="tstatus", hc_x="hydcond", hc_y="hydcond",\

rd="R", cs="cs", q="well", nf="poros", output="stresult_conf_0", dt=3600, diff_x="diff",\

diff_y="diff", c="c", al=0.1, at=0.01) # Compute the solute transport for 300 days in 10 day steps for dt in range(30):

gs.run_command("r.solute.transport", solver="bicgstab", top="top_conf",\

bottom="bottom", phead="gwresult_conf", status="tstatus", hc_x="hydcond", hc_y="hydcond",\

rd="R", cs="cs", q="well", nf="poros", output="stresult_conf_" + str(dt + 1), dt=864000, diff_x="diff",\

diff_y="diff", c="stresult_conf_" + str(dt), al=0.1, at=0.01)

# SEE ALSO¶

*r.gwflow*

*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.solute.transport source code (history)

Accessed: Saturday Jul 27 17:08:21 2024

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