Modelling Dredge Plumes for Environmental Impact Assessments

Williams, J.J.; Price, D.M.; Atan, R., Del Est al Dominguez, N., and Wright, A.P., 2024. Modelling dredge plumes for environmental impact assessments. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 589-593. Charlotte (North Carolina), ISSN 0749-0208. Dredging activities release fine sediments into the water column, forming plumes that spread horizontally, potentially impacting sensitive seabed marine communities through sunlight attenuation and siltation. Various models, normally comprising coupled hydrodynamic and mud transport modules, simulate dredging processes. However, modelling dredge plumes is challenging owing to the complexity of advection, diffusion, settlement, and resuspension of sediments. Currently, there are no standardised methods for predicting dredge plume dispersion and the potential effects on receiving environments. Most modelling studies for environmental impact assessment (EIA) are precautionary and make conservative assumptions to reduce the uncertainties in defining the nature of the bed and suspended sediments, the dredging operation and sediment losses. This approach can result in predictions of dredge plume footprints that are significantly larger than those observed during the actual dredging, leading to misinterpretations of the likelihood of potential environmental impacts. The paper draws on practical experience in recent modelling studies of dredging operations for port expansions, navigation and electrical cable installations. It describes the issues around the model set-up, parameterisation and calibration and applies a simple light attenuation model to quantify the photosynthetic impacts of dredge plumes on sensitive receptors. It highlights the problems associated with interpreting dredge plume modelling evidence for EIA purposes.