Tracer Study to Optimise Dredged Material Disposal

Identifying a New Site for the Disposal of Dredged Material in the Bonny River

The Bonny Channel Company (BCC) are responsible or undertaking maintenance and capital dredging in

the Bonny River on behalf of Nigerian Ports Authority.

With the navigational channel over 100 kilometres, dredged material is discharged offshore or in an in-river disposal site. Using the in-river site substantially reduces the haul distance, sailing times, and cost of dredging.

However, as the disposal site requires periodic dredging (which is double handling) to provide space for dredged material disposal, CARES were tasked with identifying a new location for in-river disposal. To identify the sites CARES Group collated and reviewed historical data (including quarterly bathymetric surveys); deployed, collected, and analysed MetOcean data from sensors installed on buoys and other port infrastructure; completed boat-based CTD profiling surveys; and, analysed over 2,200 sediment samples collected from a high-risk area. CARES Group also released fluorescent silt tracers from six locations to track their movement, deposition, and secondary transport over days, weeks, and months over a wide area. This enabled the development of the overall understanding of the estuary, and to know if dredged material is disposed in a specific location, where it ends up. CARES Group provided BCC an optimised dredging methodology beneficial for habitat restoration and coastal protection in an area where there are erosional concerns.

Services Provided Included:

• Tracer Study to Assess the Fate of Dredged Material

• Conceptual Model of MetOcean and Sediment Transport

• Dredged Material Disposal Sites Identification

• MetOcean Sensor Deployment, Retrieval, and Analysis

• Sediment Sampling and Laboratory Analysis (>2,200 No.)

• Boat-Based CTD Profiling Surveys