In previous years, a more generic version of the water quality model DELWAQ (module in Delft3D and SOBEK) had been developed. This version is different from the previous version due to the explicit modelling of sediment layers next to water segments. New process formulations were added and tested, in particular to improve the simulation of sediment diagenese and sediment-water exchange. One unique set of process formulations is applied for water and sediment. The extent to which and the way in which these processes are expressed depend on local conditions such as the oxygen concentration.
Improved DELWAQ offers higher simulation accuracy, more detailed water quality simulation, and much higher flexibility with regard to the processes included and spatial schematisation in an application. These innovations are important for all users of DELWAQ and for all clients who are provided with advice on the basis of DELWAQ applications.
This year, the water and sediment quality processes in new DELWAQ have been calibrated in an application for the western Wadden Sea on the basis of the GEM configuration for processes and a grid containing approximately 100 sediment compartments with 9 to 3 layers each. The initial composition of the sediment and sediment forcing functions has been imposed on the basis of zoning. All compartments that belong to the same zone are assigned the same composition and forcing functions, so that justice may be done to spatial heterogeneity in an efficient way. Literature study and evaluation of values used in previous model applications delivered ranges and starting values for all of the process coefficients. The calibration resulted both in good simulation results and a new, consistent set of coefficient values.
To enlarge the potential for the use of the model, new process routines for consolidation and erosion of fine cohesive sediment have been integrated in DELWAQ. The influence of microphytobenthos and deposit grazers on sediment stability has been included. The coupling with a new submodule for microphytobenthos submodule has also been established; the result is that DELWAQ has now become a very comprehensive framework for the ecological modelling of surface water systems. |
