8 DREDGING STRATEGY


Beneath the surface: the art of dredging


By Dr Ben Carroll*


M


aintaining an exemplary marina, which off ers an effi cient 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 cu m (65,000 tonnes) of material across its marinas, enough to fi ll more than 20 Olympic-sized swimming pools. 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 diff er 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 across the Southern half


of England. With this vast portfolio, dredging across the MDL network is an ongoing priority to ensure each marina continues to provide a second-to-none berthing and holiday experience. Each year, MDL invests up to £1 million into its dredging strategy, dependent upon the requirements across the marina group. Executing a comprehensive dredging programme in seamless conjunction with the company’s additional services is a key factor in ensuring that it off ers 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 confi ned marina basin. Due care must be taken to ensure no damage occurs to clients’ boats or the marina infrastructure, whilst also minimising any potential disruption to marina activities. In order to minimise disruption, the MDL dredging campaign is always scheduled for the period between November and March as marinas are usually quieter during the Winter. However, one potential challenge of a dredge campaign at this


MARINA ASIA-PACIFIC • FEBRUARY 2017


time of year 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. In the UK, the fi rst 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 12 months to come through, dependent upon the nature of the project, application requirements – and this includes environmental assessments – and the outcome of public consultations. 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 short to medium- term patterns in siltation across each marina to be identifi ed, allowing the company to plan dredging in future years with greater accuracy. 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. The process tends to start in early November, typically at Cobbs Quay in Poole, and then moves in an Easterly direction towards Northney and Sparkes marinas in Chichester, with completion by March. Once dredging is fi nished, a second


hydrographic survey is undertaken to ensure that target depths have been reached.


MDL Marina Consultancy consultancy@mdlmarinas.com www.mdlconsultancy.com


*Resident coastal expert and Assistant Project Manager at MDL Marinas gives an insight into the art of dredging and why this is an essential practice for all marinas.


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