Configuration file

The parameters of a simulation are given through a configuration file in a format similar to Microsoft Windows INI files. An example is given in the tutorial above. The file is separated in sections described below.


Simulation duration could be given by a combination of start time, end time and duration. If only the duration is given, the results will be written as a relative time STRDS. In case start time is given, the simulation will use an absolute temporal type.

Keyword Description Format
start_time Starting time yyyy-mm-dd HH:MM
end_time Ending time yyyy-mm-dd HH:MM
duration Simulation duration HH:MM:SS
record_step Time-step at which results are written to the disk HH:MM:SS

Valid combinations:

  • start_time and end_time
  • start_time and duration
  • duration only


Itzï does not support Lat-Long coordinates. A projected location should be used. The inputs maps could be given either as STRDS or single maps. First, the module try to load a STRDS of the given name. If unsuccessful, it will load the given map, and stop with an error if the name does not correspond to either a map or a STRDS.

The following inputs are mandatory:

  • Digital elevation model in meters
  • Friction, expressed as Manning’s n
Keyword Description Format
dem Elevation in meters map or strds
friction Manning’s n (friction coefficient) map or strds
start_h Starting water depth in meters map name
rain Rainfall in mm/h map or strds
inflow Point inflow in m/s (ex: for 20 m3/s on a 10x10 cell, velocity is 0.2 m/s) map or strds
bctype Boundary conditions type map or strds
bcval Boundary conditions values map or strds
infiltration Fixed infiltration rate in mm/h map or strds
effective_pororosity Effective porosity in mm/mm map or strds
capillary_pressure Wetting front capillary pressure head in mm map or strds
hydraulic_conductivity Soil hydraulic conductivity in mm/h map or strds
losses User-defined losses in mm/h (new in16.9, renamed in 17.7) map or strds

Deprecated since version 17.7: drainage_capacity is renamed to losses


If the selected input are located in another GRASS mapset than the current one (or the one specified in the [grass] section), you must define the full map ID (map@mapset) and add those mapsets to the GRASS search path with g.mapsets.

Boundary conditions type are defined by an integer as follow:

  • 0 or 1: Closed boundary (default)
  • 2: Open boundary: velocity at the boundary is equal to the velocity inside the domain
  • 3: Not implemented yet
  • 4: User-defined water depth inside the domain

The “open” and “closed” boundary conditions are applied only at the border of the GRASS computational region.


infiltration and any of the Green-Ampt parameters are mutually exclusives. Likewise, if any of the Green-Ampt parameter is given, all the others should be given as well.


Keyword Description Format
prefix Prefix of output STRDS string
values Values to be saved. Each one will be a STRDS comma separated list

The possible values to be exported are the following:

Keyword Description Format
h Water depth meters
wse Water surface elevation (depth + elevation) meters
v Overland flow speed (velocity’s magnitude) m/s
vdir Velocity’s direction. CCW from East degrees
qx Volumetric flow, x direction. Positive if going East m³/s
qy Volumetric flow, y direction. Positive if going South m³/s
boundaries Flow coming in (positive) or going out (negative) the domain due to boundary conditions. Average since the last record m/s
infiltration Infiltration rate. Average since the last record mm/h
rainfall Rainfall rate. Average since the last record mm/h
inflow Average user flow since the last record m/s
losses Average losses since the last record (new in 17.1, renamed in 17.7) m/s
drainage_stats Average exchange flow between surface and drainage model since the last record (new in 17.7) m/s
verror Total created volume due to numerical error since the last record (new in 17.1)

New in version 17.1: drainage_cap and verror are added.

Changed in version 17.7: drainage_cap is renamed to losses

Additionally to output a map at each record_step, h and v also produce a map of maximum values.


Water depth maps, apart from map of maximum values, do not display values under the hmin threshold (See below). When the exported map is totally empty, it is deleted at the end of the simulation.


Keyword Description Format
stats_file Statistics file CSV table

Statistics file

Changed in version 17.1: Mass balance calculation now takes into account the volume from losses. Created volume calculation is changed.

The statistic file is presented as a CSV file and updated at each record_step. The values exported are shown in the table below.

Water entering the domain is represented by a positive value. Water that leaves the domain is negative. Volumes are in m³.

Keyword Description
sim_time Elapsed simulation time
avg_timestep Average time-step duration since last record
#timesteps Number of time-steps since the last record
boundary_vol Water volume that passed the domain boundaries since last record
rain_vol Rain volume that entered the domain since last record
inf_vol Water volume that left the domain due to infiltration since last record
inflow_vol Water volume that entered or left the domain due to user inflow since last record
losses_vol Water volume that entered or left the domain due to losses since last record
drain_net_vol Water volume that entered or left the surface domain since last record due to exchanges with the drainage network
domain_vol Total water volume in the domain at this time-step
created_vol Water volume created due to numerical errors since last record record
%error Percentage of the domain volume variation due to numerical error. Corresponds to created_vol / (domain_vol - old_domain_vol) * 100

Changed in version 17.7: drain_cap_vol is renamed to losses_vol

New in version 17.7: drain_net_vol is added.


Keyword Description Format Default value
hmin Water depth threshold in metres positive float 0.005
cfl Coefficient applied to calculate time-step positive float 0.7
theta Inertia weighting coefficient float between 0 and 1 0.9
vrouting Routing velocity in m/s positive float 0.1
dtmax Maximum surface flow time-step in seconds. positive float 5.0
dtinf Time-step of infiltration and losses, in s positive float 60.0

When water depth is under hmin, the flow is routed at the fixed velocity defined by vrouting.


New in version 17.7.

This section is needed only if carrying out a simulation that couples drainage and surface flow.


This functionality is still new and in need of testing. It may be buggy. Use with care.

Keyword Description Default value
swmm_inp Path to the EPA SWMM configuration file (.inp)  
output Name of the output Space Time Vector Dataset where are written the results of the drainage network simulation  
orifice_coeff Orifice coefficient for calculating the flow exchange 0.167
free_weir_coeff Free weir coefficient for calculating the flow exchange 0.54
submerged_weir_coeff Submerged weir coefficient for flow exchange calculation 0.056

New in version 17.11: orifice_coeff, free_weir_coeff and submerged_weir_coeff are added.

The output maps are organised in two layers. The nodes are stored in layer 1, the links in layer 2.

The values stored for the nodes are described below. All are instantaneous.

Column Description
cat DB key
node_id Name of the node
type Node type (junction, storage, outlet etc.)
linkage_type Equation used for the drainage/surface linkage
linkage_flow Flow moving from the drainage to the surface
inflow Flow entering the node (m³/s)
outflow Flow exiting the node (m³/s)
latFlow SWMM lateral flow (m³/s)
head Hydraulic head in metre
crownElev Elevation of the highest crown of the connected conduits
crestElev Elevation of the top of the node in metres
invertElev Elevation of the bottom of the node in metres
initDepth Water depth in the node at the start of the simulation
fullDepth crownElev - invertElev (m)
surDepth Depth above crownElev before overflow begins
pondedArea Area above the node where ponding occurs (m²)
degree Number of pipes connected to the node
newVolume Water volume in the node
fullVolume Volume in the node when head - invertElev = crestElev

The values stored for the links are as follows:

Column Description
cat DB key
link_id Name of the link
type Link type (conduit, pump etc.)
flow Volumetric flow (m³/s)
depth Water depth in the conduit (m)
velocity Average flow velocity (m/s)
volume Water volume stored in the conduit (m³)
offset1 Height above inlet node invert elevation (m)
offset2 Height above outlet node invert elevation (m)
yFull Average water depth when the pipe is full (m)
froude Average Froude number


New in version 16.9.

Setting those parameters allows to run simulation outside the GRASS shell. This is especially useful for batch processing involving different locations and mapsets. If Itzï is run from within the GRASS shell, this section is not necessary.

Keyword Description Format
grass_bin Path to the grass binary string
grassdata Full path to the GIS DataBase string
location Name of the location string
mapset Name of the mapset string
region Name of region setting string
mask Name of the raster map to be used as a mask string

New in version 17.11: region and mask are added.

With GNU/Linux, grass_bin could be simply grass.

The region and mask parameters are optionals and are applied only during the simulation. After the simulation, those parameters are returned to the previous region and mask setting.