iMOD Python 1.0.0

iMOD Python has reached its first stable release 🎂

After 7 release candidates in 2025, we are happy to announce the first stable release of iMOD Python 1.0.0 🎉. The Deltares definition of a stable release is “Fully validated functionality with proven and reliable functionality for specific use cases and/or regions.” . The specific use cases in question here are the dutch national hydologic model (LHM) and a large solute transport model made for Flanders (Belgium). For iMOD Python, this means the following specifically:

• The API will be kept stable, and users will be warned in advance if we are going to break something.
• The software is tried and tested on 2 large, complex example models, for which we had to fix some additional bugs which we missed in small tests.
• Better stability when it comes to handling large models. We have now run weekly tests with large models. With this we can better avoid problems like performance degradation or exploding memory when working with large models.
• You can get a support contract with Deltares by contacting software@deltares.nl

The main goal of the iMOD Python 1.0.0 release was to be able to work with the dutch national hydrologic model (LHM). If you are not an LHM user, this might not sound so exciting, but you also benefit from this. The development team has worked a lot on reimplementing key features of iMOD5 and have backwards compatibility with existing iMOD5 models. To get a full overview of the current backwards compatibility with iMOD5, see this overview. The second goal of this release was to support recently added MODFLOW 6 features that can be used to achieve full feature parity with iMOD-WQ. These are parallel computation and adaptive time stepping based on the advection package.

Important highlights of features we worked on for the 1.0 release are:

• Performant regridding of entire MODFLOW 6 simulations, including regridding from structured to unstructured grids. See this user guide on all things considering regridding.
• Clip, mask, and split entire large MODFLOW 6 simulations. The latter is required to conduct parallel computations. See this example on how to split a regional model.
• Check and clean common mistakes in model input.
• Allocate topsystem packages to model layers.
• Import existing iMOD5 database and convert them to MODFLOW 6 simulations. See this example of importing an iMOD5 model and regridding it to an unstructured grid refined around the rivers
• Import MetaSWAP models from iMOD5 database. MetaSWAP is a model kernel to solve problems in the unsaturated zone, mostly used in the Netherlands.
• Write, edit and regrid MetaSWAP models on structured grids.
• Support for the AdaptiveTimeStepping (ATS) package and the ats_percel option in the Advection (ADV) package. This allows to restrict timesteps based on the Courant number in solute transport models, like was done in SEAWAT and iMOD-WQ.