UK: LAWS Achieves Great Results in Lymington
As part of the habitat improvement and erosion protection works associated with Wightlink Ltd.’s investment into upgraded ferry facilities in Lymington -(Lymington to Yarmouth IOW Service), Land and Water Services Ltd (LAWS) were contracted for the first phase of the saltmarsh restoration works.
The works comprised the collection of dredged spoils from marinas’ within the Lymington Reach and their translocation by shallow drafted barges to the Boiler Marsh which was at the Estuary Mouth in a location that was relatively difficult to access. Here the sediments were discharged by a pontoon mounted pump-ashore unit, into a shallow basin of eroded marsh which LAWS had carefully placed sediment retention fences using natural materials.
This sediment recharge project was undertaken in February and March 2012 as part of a series of precautionary measures to ensure that the integrity of the Solent Maritime European Marine Site (EMS) was not adversely affected by the proposed operation of the Lymington to Yarmouth Wightlink W-Class ferry service. The delivery of the works was sensitively timed between the periods when overwintering and breeding birds were using the site and involved considerable liaison between the Regulators, the Client, The Harbour Master, ABP mer (advisory consultant) and LAWS.
Land and Water Services Ltd were employed as Principal Contractor by the client ‘Wightlink’ to carry out these works beginning in February 2012 using their experience in working in this often hostile and remote environment. Land and Water Services were able to supply all the specialist equipment and expertise necessary to complete the contract in-house.
The first challenge was the installation of the sediment retaining structures which were constructed using straw and heather bales secured with chestnut stakes. These structures were sensitively positioned across inlets and channels. These structures serve to retain the recharge materials that were pumped into the eroding marsh and in the future will help to encourage natural settlement and also to reduce the wave energy exposure of the eroding marsh habitat.
LAWS mobilised one of their specialist amphibious excavators to construct the retaining structures as described above. The low ground pressure machine travelled across the estuary and worked comfortably in the soft terrain with the minimum of impact. The excavator was also used to deploy and position the discharge pipeline across the saltmarsh.
Land and Water’s new river class tug, Clyde, and shallow drafted mud-hoppers were used to transport silts between the recovery and discharge sites, cross-navigating busy shipping lanes, requiring maximum communication during operations.
A pontoon mounted excavator and pumping system was then used to discharge excavated material, recovered from the marinas located on the opposite side of the marsh. The Pump-ashore unit was used to pump the dredged materials up to 900 meters onto the salt marshes. Innovative thinking was required by LAWS to overcome some difficult pumping conditions, with exceptionally cold weather conditions dropping as low as -12 degrees.
Works took place within difficult tidal ranges offering only small operational windows, requiring extreme attention to detail and awareness of the surrounding and tidal conditions. Some delays were experienced due to weather conditions and tidal conditions meaning that the site was often completely inaccessible (dry!). Even with these conditions Land and Water met all contractual and environmental deadlines.
Several regulatory, statutory and professional bodies had a keen interest in these highly sensitive saltmarsh works, including the Marine Management Organisation (MMO), the New Forest National Park Authority, the Environment Agency and Natural England.
Colin Scott, Managed Realignment and EIA Specialist, of ABP Marine Environmental Research (ABPmer) who advised throughout this project presented the initial findings from this work at the Central Dredging Association’s (CEDA’s) workshop on the use of Dredged Material on 8th May 2012. He commented that:
“Land and Water’s Senior Site Manager, Graham North, and his team did a superb job on the Boiler Marsh Sediment Recharge project at Lymington. The team worked in tough conditions in mid-winter to create what already (2 months later) is looking like an effective habitat restoration. However, the work will be subject to on-going monitoring to verify the findings and will be overseen by a specialist panel of regulators and stakeholders who will advise further on its effectiveness. I am confident though that this will provide valuable lessons for the future management of marshes in the Solent and the rest of the UK. ”
Dredging Today Staff, May 22, 2012; Images: land-water