Hydrodynamical Models

OD Nature studies the ecosystems of the North Sea using mathematical models. We translate the mechanisms (currents, waves, biological and sedimentation processes...) that regulate the action of the sea into mathematical formulas. These are then incorporated into a system of comparisons in a grid for the area we want to model. The comparisons are converted into computer programs for processing on powerful computers to obtain a faster calculation.

Hydrodynamical models
Models

The mathematical models are made for physical variables (water height, currents, waves, temperature, salinity), chemical variables (mainly hydrocarbons), biological variables (limited to the first links in the food chain), sediment transport and transport of other (potentially polluting) substances such as oil slicks, and for the calculation of changes in the form and composition of the sea bed. These variables are inter-related, the level of complexity and uncertainty increasing as you move from the physical to the biological and to the sediment.

The results of the models are then carefully compared with all the available observations made on trips to sea, by measuring instruments on the sea surface or the sea bed and satellite observations. This is the “validation phase”. If the results of the validation are insufficient, this means that the mathematical formulas selected to describe the processes are inadequate. If the validation results are sufficient, this means that the models can be used for sea management and in predicting parameters. This enables the reduction of uncertainties in the results calculated by the model by, for example, better adjusting the parameters. A more advanced technique is data assimilation whereby forecasts made by the model are adapted to the observations during the actual simulation. The method also enables the calculation of a margin of error.

The models are, above all else, research instruments with which to test scientific hypotheses in a virtual manner. In that case we speak of models in development. As soon as these models show an acceptable reliability we speak of operational models. These models can provide a variety of information on the sea (forecasts of water height, currents, waves, etc.); just as mathematical models can be used to forecast weather.

Waves
COHERENS

The hydrodynamic model that OD Nature has developed and is further refining is the three-dimensional COupled Hydrodynamic Ecological model for REgioNal Shelf seas (COHERENS) model. This model is designed especially for shallow waters, such as along our coast, and for estuaries and lakes. It is available free of charge to the scientific world and is already used in more than 90 countries! 

In spite of the complexity of the current generation of sea models and growing computer capacity we must always consider the results of the simulations as an approximation of the actual situation at sea, they do not replace observation. The major advantage is that digital simulations have a global dimension and as a consequence have a greater range in space (via a fine grid) and time (both in the past, the present and the future).  Specific applications are:

  • Operational forecasts of water height (at sea and along the coastline) and currents for the coming days;
  • The evolution of oil slicks;
  • Transport of fish larvae, which is important for the evolution of fish stocks in the future;
  • Erosion or sedimentation of coastal districts and channels;
  • Climate forecasts for the coming decades;
  • Algal bloom;
  • Studies of biodiversity in protected nature reserves;
  • Designs of specific scenarios such as the effect of a super storm, the consequences of a shipping accident at sea, the calculation of parameters for the design of coastal protection structures,…
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