Portsmouth Main Channel Dredge

Geomorphological desk assessment and numerical plume modelling to inform dredge EIA

The main entrance channel to Portsmouth Harbour required deepening to be able to accept the new Royal Navy Aircraft carriers.

ABPmer was contracted to undertake the geomorphological desk assessment and numerical plume modelling to inform the environmental impact assessment for the Portsmouth Main Channel Dredge and associated infrastructure (Middle Slip Jetty) for the new aircraft carriers.

The study involved determining a conceptual understanding of the flow and sediment regime of the harbour from existing data and field measurements across the entrance channel.

The data was then used to construct and calibrate numerical wave and flow models, used to assess the physical environmental impacts of the dredge and plume simulations of the dredging operations.

As part of the commission we also provided advice through the team to Defence Estates and Environment Agency on extreme water levels (flood risk) and predictions on long term habitat change (for the Habitat Regulations Appraisal).

As a follow on, ABPmer was employed to assess the effects of further modifications to the harbour, advise on the potential environmental effects of using Water Injection Dredging to assist the capital dredge, to remove soft sediment to aid the identification of and the safe removal of UXO.