Modelling and monitoring of dredged sediment dispersal Brightlingsea UK
CEDA Dredging Days 2017 - Sustainable Dredging - Continued Benefits
Coulet W., Rotsaert M., de Wit L., Manning W.
Abstract: The Waterside Marina located within the Colne Estuary, Essex, UK, is subject to sedimentation and in the last few years this has accumulated to approximately 11,000 m3 of sediment. Dredging on a regular basis is necessary to keep the marina accessible and operational.
The permit for the maintenance dredging had expired. Additionally, changes to regulations in combination with an ecologically sensitive environment; oyster fisheries and key sites for overwintering and breeding birds, make permit applications for dredging challenging. A study on the dispersal of dredged material within Brightlingsea Creek and the River Colne was required, as this has been highlighted as the most cost effective and environmental conscience method.
Environmental data was collected by completing hydrographic, topographical, oceanographic, climate, surveys and sediment characterisation. This data was then utilised for the numerical hydrodynamic model FINEL. This model simulates flow and transport processes in river and coastal waters. It encompasses robust procedures for ebbing and flooding tides on the intertidal sections and contains extensive parameterization of the sediment transport, thus allows modelling the morphology in the estuary.
The output of the model predicts the dispersal of dredged sediment on an ebbing tide from the discharge point. The modelling was helpful in determining a strategy that spares key oyster beds, which are one of the most sensitive receptors in the estuary, of the accumulation of sediment.
Through monitoring of the actual dredging and dispersal, the concentrations from the model were verified. The monitoring ensured that dredging and dispersal was carried out in an adaptive manner, enabling the movement of the discharge point to optimum positions in the tidal flow. The adjustment of the discharged sediment/water ratio also benefitted the dispersal process. The marina was successfully dredged in March 2016 on the basis of the predictive model and adaptive management of the dredging process.
Key words: modelling, adaptive management, monitoring, Environmental Impact Assessment, dispersal