imod.evaluate.facebudget(budgetzone, front=None, lower=None, right=None, netflow=True)[source]#

Computes net face flow into a control volume, as defined by budgetzone.

Returns a three dimensional DataArray with in- and outgoing flows for every cell that is located on the edge of the control volume, thereby calculating the flow through the control surface of the control volume.

Front, lower, and right arguments refer to iMOD face flow budgets, in cubic meters per day. In terms of flow direction these are defined as:

  • front: positive with y (negative with row index)

  • lower: positive with layer (positive with layer index)

  • right: negative with x (negative with column index)

Only a single face flow has to be defined, for example, if only vertical fluxes (lower) are to be considered.

Note that you generally should not define a budgetzone that is only one cell wide. In that case, flow will both enter and leave the cell, resulting in a net flow of zero (given there are no boundary conditions present).

The output of this function defines ingoing flow as positive, and outgoing flow as negative. The output is a 3D array with net flows for every control surface cell. You can select specific parts of the control surface, for example only the east-facing side of the control volume. Please refer to the examples.

  • budgetzone (xr.DataAray of floats) – Array defining zones. Non-zones should be with a np.nan value. Dimensions must be exactly ("layer", "y", "x").

  • front (xr.DataArray of floats, optional) – Dimensions must be exactly ("layer", "y", "x") or ("time", "layer", "y", "x").

  • lower (xr.DataArray of floats, optional) – Dimensions must be exactly ("layer", "y", "x") or ("time", "layer", "y", "x").

  • right (xr.DataArray of floats, optional) – Dimensions must be exactly ("layer", "y", "x") or ("time", "layer", "y", "x").

  • netflow (bool, optional) – Whether to split flows by direction (front, lower, right). True: sum all flows. False: return individual directions.


  • facebudget_front, facebudget_lower, face_budget_right (xr.DataArray of floats) – Only returned if netflow is False.

  • facebudget_net (xr.DataArray of floats) – Only returned if netflow is True.


Load the face flows, and select the last time using index selection:

>>> import imod
>>> lower ="bdgflf*.idf").isel(time=-1)
>>> right ="bdgfrf*.idf").isel(time=-1)
>>> front ="bdgfff*.idf").isel(time=-1)

Define the zone of interest, e.g. via rasterizing a shapefile:

>>> import geopandas as gpd
>>> gdf = gpd.read_file("zone_of_interest.shp")
>>> zone2D = imod.prepare.rasterize(gdf, like=lower.isel(layer=0))

Broadcast it to three dimensions:

>>> zone = xr.ones_like(flow) * zone2D

Compute net flow through the (control) surface of the budget zone:

>>> flow = imod.evaluate.facebudget(
>>>     budgetzone=zone, front=front, lower=lower, right=right
>>> )

Or evaluate only horizontal fluxes:

>>> flow = imod.evaluate.facebudget(
>>>     budgetzone=zone, front=front, right=right
>>> )

Extract the net flow, only on the right side of the zone, for example as defined by x > 10000:

>>> netflow_right = flow.where(flow["x"] > 10_000.0).sum()

Extract the net flow for only the first four layers:

>>> netflow_layers = netflow_right.sel(layer=slice(1, 4)).sum()

Extract the net flow to the right of an arbitrary diagonal in x and y is simple using the equation for a straight line:

>>> netflow_right_of_diagonal = flow.where(
>>>    flow["y"] < (line_slope * flow["x"] + line_intercept)
>>> )

There are many ways to extract flows for a certain part of the zone of interest. The most flexible one with regards to the x and y dimensions is by drawing a vector file, rasterizing it, and using it to select with xarray.where().

To get the flows per direction, pass netflow=False.

>>> flowfront, flowlower, flowright = imod.evaluate.facebudget(
>>>    budgetzone=zone, front=front, lower=lower, right=right, netflow=False
>>> )