The task The solution HDLite FlexSim Horsens fjord

1. FlexSim- a simple but flexible tool for ecological fjord modeling. • The task • The solution • HDLite • FlexSim • Horsens fjord

2. The task • Make a modeling tool to: • estimate fjord modification of loads from the Danish watersheds in different scenarios • assess the ecological state in Danish fjords in different scenarios • The tool must be: • easy to implement on new fjords • have computational times in the order of minutes for yearly simulations • Wish list: • Decouple physics and biology • Separate biological and programming expertise

3. The solution • FlexSIM • Model setup including the ecological equation system is inputted to a precompiled model engine. • Highly flexible enabling both very fast ‘box’ setups and high resolution 3D computational grids. • HDLite: Combined box model-3D model concept • Water volumes are exchanged between cells as in a box model • Fluxes between boxes are automatically calculated from the computational grid geometry and simple physical assumptions: • Stratification is created by freshwater runoff in the surface and penetration of denser salt water from the open boundaries by horizontal mixing. • Stratification is eroded by wind induced vertical mixing. • The timestep is limited only by the size of the cells and the mixing coefficients

4. Horsens fjord Bathymetry

5. Horsens fjord Salinity Course box model 1 year HDLite only in ~10 sec. Timestep = 3600 sec. Mixed mesh model 1 year HDLite only in <10 min. Timestep = 120 sec.

6. Modeling without programming… • Copy the model engine executable to your windoze computer • Use a text editor to create or modify mesh, bathymetry and setup files • Run the engine from the command prompt with your setup file as input