To initiate a groundwater flow model simulation using iMODFLOW a Runfile is required. This file describes:
• the location of the (sub)model;
• the simulation time (number of stress periods);
• the current distribution of computational nodes (grid size);
• the current number of model layers to be used;
• the collection of files that describe the model parameters;
• the desired output variables to be saved.
A Runfile gives an overview of the entire model configuration and is therefore easy to transfer and reproduce. A major difference between the input files necessary for other conventional simulators (e.g. standard Modflow) is that a Runfile does not contain any model data, unless a constant value is assigned to a model parameter. It consists mainly of references to other files (IDFs, IPFs, ISGs, GENs) that contain the actual model data.
The philosophy of using iMODFLOW and the concept of a Runfile is that all the referred files are constructed for a REGION of interest rather than for an AREA of interest. A REGION of interest can be extremely large (provinces, countries); an AREA of interest is often smaller (watersheds, water management areas). The central idea is that model data is collected for large regional areas at the finest scale available for that type of model data, e.g. land use observations at a resolution of 100 x 100 meter and precipitation distribution at a scale of 1000 x 1000 meter. These files are referred to in the Runfile and iMOD combines the different data to the desired AREA of interest and resolution at the moment a simulation will start. Simulations for different AREA‘s of interest can be performed using identical model data that need to be maintained at a single location.
This chapter covers the Runfile-related topics:
• section 10.1: the general structure of a Runfile.
• section 10.22: Runfile-history: any differences between Runfile-structures per iMOD release.
• section 10.23: all options of how a Runfile can be used to start a MODFLOW simulation.
• section 10.24: an example of printed MODFLOW output.
• section 10.25: a table containing the names and content of the output folders.