ALL AT SEA MARCH 2021
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THE CHANGING FACE OF MARINAS When we visit a marina, we notice the state-of-the-art facilities, the cleanliness of the marina and the quality of the pontoons. But what we do not see is what goes on below the surface.
Hamble Point Marina
M
DL Marinas has just finished dredging its Sparkes and Northney marinas in Chichester, the culmination of its £400K 2020/21 winter dredging programme. This year MDL dredged enough silt and mud from its marinas to fill 10 Olympic sized swimming pools, weighing 33,000 tonnes, which is the equivalent of 8,000 elephants or the Spinnaker Tower in Portsmouth. This amount of dredging, and much more in some years, is essential to providing year-round all tides access to MDL’s marinas for berth holders and visitors. As with many marinas globally, MDL’s marinas are subject to ongoing siltation and require regular dredging to maintain water depths. This ensures boats do not run aground on the approach and are able to berth safely and stay afloat once inside the marina. “The results of the investment in our comprehensive dredging programme Northney Marina
are probably the least visible of all our investments,” says Alex Beere, MDL’s director of technical services. “But it would soon be very noticeable if we did not complete this essential work annually, and would heavily impact on a customer’s experience of our marinas.” “Key to providing a second to none marina experience is the provision of excellent infrastructure, and 24 hour access to our marinas. Dredging is the core activity that allows MDL to maintain all tides access.”
Variable Requirements
Siltation is the natural process of sediment deposition, with a proportion of the sediment (or mud particles) suspended in the water settling on the sea or riverbed when water is static or slow moving. The issue is exacerbated by erosion of riverbanks further upstream or heavy rainfall depositing mud into the river, along with material washing in with the tide.
Dredging work at Northney Marina
Each of MDL’s marinas is situated in its own unique location meaning it is subject to its own individual range of tidal and physical factors. Therefore, the pattern and scale of siltation will differ between the marinas in MDL’s network, with no two marinas’ dredging requirements ever being the same.
Minimal Disruption
Excavating accumulated sediment requires a large dredge to be operated with extreme care within the marina, ensuring no boats, marina pontoons or piles are damaged. To minimise disruption to marina activities, MDL always schedules the dredging during the winter months, typically November to March when many boats are out of the water and visitor levels are reduced. MDL is able to further manage the disruption by rotating which marinas are dredged each season and mostly dredging specific sections only, rather than the entire marina. The selected sections are dredged on a cycle, with the whole marina being dredged over a three to five-year period. Cobbs Quay, Saxon Wharf, Hamble Point, Northney and Sparkes, including part of the navigation channel, featured in MDL’s 2020/21 dredging schedule.
Planning for Success
Due to strict legislative requirements, the dredging programme takes careful planning with extended lead times. First off, MDL applies for a marine licence from the Marine Management Organisation, which permits dredging and disposal activities. This licence can take up to 12 months to come through, depending on the scope of the project, and includes an environmental assessment, ensuring that MDL’s dredging proposal will not adversely affect the local marine environment.
MDL also obtains consent from the Harbour Authorities within whose areas it operates. They ensure, in addition to environmental protection within their boundaries, that safe navigation is not compromised during the dredging activity. Once the marine licence is in place, MDL starts planning the annual dredge campaign. This planning usually starts in June with hydrographic surveys of the marinas subject to high levels of siltation. These surveys provide a picture of the existing depths across the marinas and allows MDL to review potential dredging requirements. The hydrographic surveys also help to identify short to medium-term patterns in siltation across each marina, enabling MDL to plan dredging in future years. Dredging at MDL’s marinas based in the Solent area is carried out by local contractor, Jenkins Marine, while elsewhere it is tendered separately across different contractors depending on location. Now the dredging for this season is complete, a second hydrographic survey will be undertaken to ensure target depths have been reached and berth holders and visitors can enjoy unfettered access to their berths. MDL spent £400K on dredging this year to maintain the necessary depth in the marinas for all tides access, but some years the annual dredging requirements can be as high as £1m. To find out more about MDL’s marinas visit www.mdlmarinas.co.uk.
