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Estuary Sedimentation Management in Cowes Harbour

Sediment Management and Dredging

Cowes Harbour Commission (CHC) is committed to environmental management and protection of the natural estuary habitat. CHC's guiding policy on dredging management is to coordinate maintenance dredging activities to maintain a sustainable balance between navigational requirements and natural estuarial features. 

The plan to develop and agree a ‘Sustainable Maintenance Dredging Management Plan’ for the Medina Estuary was first proposed in the Commission’s Strategic Framework of 2011 and has been reiterated in CHC’s current Strategic Plan 2016-2021.

CHC's aim is to develop a new cost-effective 'Medina Estuary Sustainable Maintenance Dredging Management Plan' in partnership with stakeholders that is underpinned by long-term monitoring and promotes alternative dredging methods. Under the proposed plan, maintenance dredging activities would be coordinated to maintain, as far as is possible, a sustainable balance between navigational requirements, harbour improvements, and natural estuarial features. The plan could bring considerable benefits to stakeholders, including cost efficiencies through the roll-out of partnership surveying and a CHC-facilitated consenting process, as well as benefits to the environment with a review of dredging methods utilised.

In 2015, CHC commissioned an initial field-based study by an independent estuarine consultant scientist, Dr Rob Nunny, to provide further understanding and complementary advice to the extensive modelling studies already undertaken of how sediment is moving around the harbour. The study aimed to confirm the types of sediment present and the tidal and meteorological forces that may be controlling the processes of sedimentation. From this initial study, Cowes Harbour Commission decided to instigate a long-term project to constantly monitor the flux of fine sediment through the lower estuary and survey annually any changes to the estuary's form and depth.

The sediment monitoring programme analyses each year’s robust data collection. Data includes multi-beam surveys of the whole harbour that give a 3D image of the estuarine basin, and continuous sediment monitoring from selected monitoring stations around the estuary. Data from the monitoring stations confirms the actual amount of sediment in the water column at each station throughout the year. Dr Rob Nunny’s reports analyse the data and detail his findings and conclusions. The evidence and conclusions from these studies provide the Commission with a high level of confidence and understanding on how the Medina Estuary is functioning and developing, underpinned by robust monitoring and modelling. This level of sedimentary data, studies and understanding on how our estuary is functioning is probably unrivalled in the UK and places the Commission in a good position to start developing a Maintenance Dredging Management Plan. CHC has been consulting with the main dredging stakeholders in the harbour for the last few years on this project with significant support for this important environmental and sustainability project, however, there are currently still concerns from some dredging stakeholders with some of the alternative environmental management options, such as the Water Injection Dredging.

CHC has prepared a summary report entitled 'THE NATURAL ENVIRONMENT OF THE MEDINA ESTUARY AND COWES HARBOUR', which has been reviewed by Dr Rob Nunny. CHC’s report is aimed at providing an overview and understanding of how the estuary is functioning and developing, together with a high-level summary of this important project for the future sustainability and management of the Medina Estuary.

Sediment Flux Measurement in the Medina Estuary: Monitoring Results
(Author: Dr R. S. Nunny BSc. PhD.)
Year 4: 2019 Report
Year 3: 2018 Report
Year 2: 2017 Report
Year 1: 2016 Report

Sustainable Sedimentation Management in the Medina Estuary: Study Reports
Report: March 2018 (Dr R Nunny): 'Sustainable Sedimentation Management in the Medina Estuary: A Forward Look at Maintenance Dredging Needs, Practices and Management'
Summary of Report: April 2018 (CHC): 'Studies on Estuary Sedimentation Management'

Report: 2016 (Dr R Nunny): 'Sediment Management in the Medina Estuary Monitoring Results'
Summary of Report: May 2017 (CHC): 'Estuary Sedimentation Management & Development of a Maintenance Dredging Management Plan'

Sedimentary Processes: May 2016 (Dr R Nunny): 'Sedimentary Processes in the Medina Estuary'
Appendices: May 2016 (Dr R Nunny): 'Sedimentary Processes in the Medina Estuary'

Monitoring Initiation: February 2016 (Dr R Nunny): 'Medina Estuary Sediment Management Strategy: Monitoring Initiation'

Beneficial Use of Dredged Material
The work on sediment management and dredging also links with saltmarsh management in the Medina as there is evidence from other coastal areas that adding sediment and retaining it around the marshes will help to re-establish the habitat and reduce further loss. CHC is also working with the Solent Forum on a project to use dredged material beneficially within the Solent to assist with habitat re-creation and flood management. More information about beneficial use studies can be found on the Solent Forum’s website.

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