Focus

The mixing process on and above the structured permeable seabed is investigated in a defined laboratory experiment to foster our understanding of turbulence and mixing in shallow coastal waters. The resulting parameters regarding the fluid flow, scalar transport and mixing are provided as boundary conditions for the modeling of the large scale transport process.

State of the Art

The convective transport of substances with the ocean currents plays an important role for the balance of the ecosystem within the Baltic ocean. On the one hand the scalar transport has been intensely investigated with respect to the inflow mechanisms regarding the influence of the North Sea. On the other hand there is only little information available on the mechanisms of mixing due to waves and turbulence over sloped or structured seabeds near the coastline. In particular, the interaction between a permeable seabed with a permanent inflow of groundwater and the periodically oscillating bottom boundary layer has so far not obtained much attention. The interaction between these two fluid domains can be regarded as the gateway towards a mixing process, which explains the subsequent transport of substances into the water column that were transported from land to the pores of the seabed with the groundwater.

Work program

In the first phase we will develop and design a laboratory experiment with a permeable seabed which will allow measurements of the flow characteristics, turbulence and mixing properties. The experiment is based on our research on transition and turbulence in internal waves. A water channel, which provides a flow field over a modeled ocean floor with variable surface structures, is already in operation. The future experiment will use the laser optical methods PIV (particle image velocimetry) and LIF (Laser induced fluorescence) in the water column, with both measurement devices being already available. The flow field, turbulence and mixing data will be transferred between the projects within Baltic TRANSCOAST to allow a quantitative modeling of the flux of the substances, which were transported from the sources on land to the ocean currents of the Baltic Sea via the groundwater.