Beneath the Surface: The Art of Dredging at MDL Marinas

Posted: 15th February 2017

Maintaining an exemplary marina which offers an efficient service is the utmost priority for all marina managers. Much of the work at a marina takes place under the surface and MDL Marinas is using comprehensive methods to maintain its marinas, particularly through its annual dredging strategy. Last year MDL dredged in excess of 50,000 m3 (65,000 tonnes) of material across its marinas, enough to fill more than 20 Olympic-sized swimming pools. In-house expert and Assistant Project Manager at MDL Marinas, Dr. Ben Carroll, shares his insight into the art of dredging and why this is an essential practice for all marinas.

Ben comments: “Marinas across the world are, for the most part, subject to constant siltation and many require regular dredging to maintain water depths, which ensures boats don’t run aground and have safe access when mooring. The pattern and scale of siltation at any given marina will depend on a unique range of physical factors, which will inherently differ between sites. Therefore, the dredging requirement of any two marinas will never be the same.

“MDL Marinas is the UK’s leading marina operator, with 18 marinas positioned in the UK. With this vast portfolio, dredging across the MDL network is an ongoing priority to ensure we continue to provide a second to none berthing and holiday experience. Each year MDL invests up to £1million into its dredging strategy, dependent upon the requirements across the marina group. Executing a comprehensive dredging programme in seamless conjunction with our additional services is a key factor to ensuring MDL offers a competitive and world-leading marina portfolio for boaters to enjoy.

“In many respects, dredging is seen as a necessary evil, with a degree of disruption inevitable when operating large mechanical equipment within a confined marina basin. Due care must be taken to ensure no damage occurs to customer boats or the marina infrastructure, whilst also minimising any potential disruption to marina activities. In order to minimise disruption, we always schedule the MDL dredging campaign for the winter period, between November and March, when the marina is usually quieter. However, one potential challenge of a winter dredge campaign is the risk of delay due to bad weather, whereby disposals to sea are hindered. This should always be factored in when undertaking a winter dredging programme and contingency plans should be considered in the event of unpredictable weather.

“The path to undertaking dredging requires meticulous planning as there are strict legislative requirements to adhere to. The first step of planning is the granting of a marine licence from the Marine Management Organisation, which permits dredging and disposal activities.  A marine licence can typically take between six and twelve months to come through, dependent upon the nature of the project, application requirements – which includes environmental assessments - and outcome of public consultation.

“Once a marine licence is in place, the planning of the annual dredge campaign usually starts in June, when hydrographic surveys are arranged for marinas subject to high levels of siltation. These surveys provide an invaluable picture of the existing depths across the marinas and allow MDL to review potential dredge requirements. The hydrographic surveys also enable us to identify short to medium-term patterns in siltation across each marina, allowing us to plan dredging in future years more accurately.
“Dredging at MDL Marinas in the Solent region is carried out by a single contractor, whilst elsewhere it is tendered separately to a number of contractors. Dredging tends to start in early November, typically at Cobb's Quay in Poole and then moves in an easterly direction towards Northney and Sparkes marinas in Chichester, completed by March. Once the dredging has been completed, a second hydrographic survey is undertaken to ensure the target depths have been reached.”