Satellite based dredge plume monitoring to protect coastal ecosystems

Dredging operations are essential to protect coastlines, safe navigation and ensuring access to harbours. With threats of sea level rise, flooding and more extreme storms, the need for dredging operations will only increase and their sustainable implementation will be key.

One of the key aspects to control during dredging, is the release of sediments in the water and increase of turbidity during dredging, which can degrade water quality and harm sensitive ecosystems. Imposing turbidity limits where dredging contractors have to comply with, is common in most parts of the world. However, there are various sources of turbidity near the dredging area: from resuspension, to dredged bottom sediments and outflows from rivers. Hence, a turbidity increase is not necessarily linked to a (nearby) dredging activity. It is therefore key to understand the extent of the dredge plume and natural background turbidity to avoid unacceptable ecological impacts, adhere to the directives in place but also to avoid unnecessary shutdowns.

We have developed a method for a dedicated dredge plume monitoring based on Earth Observation data. This method allows to assess the turbidity of the dredge plume but also its extent and impact on the nearby ecosystem. First, a satellite database of dredge plumes was compiled, including several large dredging sites around the world. The database is complemented with an automated Artificial intelligence based plume delineation. This plume delineation automatically recognizes the plumes in the images and derived the near field dredging plume. In a second step, optical properties of the dredge plumes are evaluated. This is done by developing a dredge plume spectral library from the database and by collecting field samples during dredging activities. These field samples are analysed and interpreted to understand their optical properties (light attenuation, absorption, scattering and backscattering, turbidity and fluorescence per units of suspended particulate matter and chlorophyll-a concentrations). Finally we will present the results of our new dredge plume algorithm, adapted for the specific conditions of a dredging site.