The bed morphology of dynamic surface water systems has always fascinated people, not only for safety reasons related to e.g floods and environmental disasters, but also for the wish to understand and predict the impacts of the ever increasing human interference with these systems. Understanding and predicting biogeomorphological processes, however, involves a wide range of disciplines such as hydrodynamics, hydrology, geology, chemistry, biology, ecology, oceanography and civil- & environmental engineering. If new insights need to be implemented, disciplines like social sciences, public administration, law and economy also come into play.

The improved understanding of biogeomorphological systems shows that their behaviour is governed by complex interactions between a number of physical and ecological processes and the morphological changes they cause. Yet, knowledge gaps remain due to the complexity of the processes and their interactions in natural systems. Successful application of (numerical) biogeomorphological models in realistic situations therefore requires expertise and a good overview of what is known and where the uncertainties are.

Driven by the increasing insight into the role of biota in geomorphology, the interdiscipline biogeomorphology is developing and biogeomorphological models are being set up which integrate hydrodynamic, morphological, water quality and ecological processes and their interactions at relevant scale levels. The model system described herein belongs to this category. For the time being, it focuses on coastal and estuarine applications.The biogeomorphological coastal modelling system has been validated against typical analytical solutions, flume experiments and a practical application (Ye, 2012). Furthermore, the system was tested in various practical applications, as described below.

When using Delft3D-FLOW for the hydrodynamics, one can couple the Delft3D-WAQ module using the communication file from the flow model. The Delft3D-FLOW and Delft3D-WAQ models can be build separately, for instance in the associated graphical user interface (GUI). For online-coupling between Delft3D-FLOW and Delft3D-WAQ, first set up a flow model and tick the online-coupling box for WAQ. Furthermore, a coupling interval (indicated as the communication file interval) must be specified (see image). Activating the online coupling with Delft3D-WAQ initiates the WAQ-GUI upon execution of the flow model. This enables setting up the WAQ model like in a stand-alone or offline coupled case. Note that the specified coupling interval should be identical to- or a multiple of the communication file time interval.

More advanced options are available, for instance using keywords, etc. Here we refer to the various Delft3D manuals, for instance on the OSS-manual page page, as the entire biogeomorphological coastal modelling system is elaborately described in these manuals. The standard Delft3D release (trunk) contains a coupling program (with Delft3D-WAQ) for the biogeomorphological coastal modelling system. The bed state module, vegetation population dynamics module, sediment transport module and geomorphological bed updating module are part of the trunk Delft3D-WAQ release.

Delft3D is open source and can be obtained for free at the OSS-site. As of 01-01-2013, Delft3D-WAQ is open source as well, making the biogeomorphological coastal modelling system completely open source. The open-source version of Delft3D-WAQ is also available at the same location as the open-source version of Delft3D-FLOW. Currently, interested users can obtain a precompiled version of the entire Delft3D-suite (including FLOW, WAVE, WAQ, MOR, PART, etc.).

^{For Delft3D open-source users: the GUI can be be requested here.}

Relevant software

Delft3D:

• Source-code (OSS account required)
• Delft3D-Suite, a precompiled version of the entire Delft3D-suite (including FLOW, WAVE, WAQ, MOR, PART, etc.).
• D-Flow FM

• Schwarz, C., Ye, Q., van der Wal, D., Zhang, L., Ysebaert, T., Herman, M.J.P., 2013. 'Impacts of salt marsh plants on tidal channel initiation and inheritance' 
• Ye, Q., 2012. 'An approach towards generic coastal geomorphological modelling with applications', Delft University Institutional Repository