iMOD User Manual version 4.4 (html)

12.27ISG iMOD Segment package

The iMOD Segment package defines the surface water system with an ISG-file which contains all relevant information used by surface water elements which are in direct relation with groundwater. The ISG-file stores:

To store all these different types of information the ISG-file format consists of associated files that are connected by the ISG-file. The ISG package as is, is not available in MODFLOW, but it generates the input for the conventional RIV package. For the SFR package (see section Section 12.28), this type of an ISG file is expanded with more data, see section Section 9.9 for a detailed description of both types of ISG files.

The ISG package file format is based on vectors and time series and therefore has a much more efficient disk use than the RIV package. iMOD and iMODFLOW both, can handle those ISG files to generate model input. Within ISG Edit (see section Section 6.10.3) it is possible to compute IDF files from the ISG file for the different model parameters such as conductance, stage, bottom heights and infiltration resistances. Or, more efficient, it is possible to use the ISG directly in the RUN- and/or PRJ file and let iMOD/iMODFLOW grid the ISG file internally to a conventional/modified RIV-file, see section Section 10.11.

The way iMOD/iMODFLOW grids the vector based ISG file onto the simulation raster is as follows.


Figure 12.14: Example of the conductance (m\(^2\)/d) of a segment (red line) in an ISG file gridded on a model network.

The cross-sections in a ISG can yield different appearances of the conductance and therefore the outline of the segment in the model network. The following configurations might occur:


Figure 12.15: Example of the brush method; (left) showing the fractions for the first location of the brush; (right) showing the updated and new fractions when the brush is moved one row down.

Each of the above mentioned configuration yield a different assignment of conductances to the underlying model network, as shown in the following figure.


Figure 12.16: Example of different conductances for a segment in an ISG file gridded on different model network with and without local sub grid refinements and for different type of cross-sections.

The ISG file format also makes it more easy to convert a surface water model data from SOBEK into iMOD using the SOBEK import tool.