The Severn Estuary – A Challenging Environment – Jerry Stanford

Published on April 27, 2017 in 2017 Forum Reports, Economy, Energy, Environment, Presentation

Jerry Stansford - Bristol Port at Sustainable Severn Forum 2017Jerry Stanford, Haven Master, Bristol Port Company continued the talks on the session theme of Governance and collaboration.

During his talk he shared the role of Bristol Port and the challenging environment of the estuary and on how they need to manage mud on a grand scale and the marine operations involved and longer term changes and challenges.

In his talk, Jerry outlines that Bristol Port :

  • Major UK Port
  • Harbour Authority
  • Sustainable Developer
  • Decades of experience of operating in the challenging environment of the Severn Estuary.

The Severn Estuary – a challenging environment:

  • Third highest tidal range in the world (over 14.5m)
  • Strong tidal currents (4m/s or 8 knots at the Shoots/Severn Bridges).
  • Highly mobile sandbank features
  • Huge suspended sediments loads (estimated over 30 million tonnes in the Estuary on a Spring tide)
  • These muds settle on to the seabed on Neap tides
  • Over large areas of the Estuary average suspended sediment levels are >1,000 mg/l, while locally average bed levels can exceed 15,000mg/l

Managing mud on a grand scale!:

  • Muds are deposited in Portbury Entrance at a rate of around 0.1m/week
  • Muds are deposited in Avonmouth Entrance at a rate of around 0.1m/month
  • Around 1.5 million m3 of muds are dredged from the dock entrances each year and placed at nearby licenced disposal sites
  • Around 4 million m3 of muds per year are dredged from within the Docks and discharged via pipelines into the estuary.

Marine Operations – Maintenance Dredging:

  • Dredging is a statutory duty required to provide safe navigable depths for commercial shipping
  • High suspended sediment levels in the Estuary means that the Docks and their entrances require regular maintenance dredging
  • Dredging has taken place here for over a century
  • Dredging is highly localised to the docks and their immediate entrances (around 1km2)
  • The main navigation channel in the estuary is not dredged (it’s naturally scoured by tides)

Summary:

  • Challenges:
  • Large scale natural changes
  • Monitoring and evidence
  • Uncertainty and risk
  • Difficulty in predicting changes or trends/modelling
  • Unintended consequences
  • Sedimentation and dredging
  • Abrasion of marine structures

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