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Quayside Suite
Medina Chambers
Town Quay
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2014
Beneficial use of dredged sediment
United Kingdom
Lymington Estuary (Hampshire)
-1.5056473
50.748649
Mudflat
1.5 Hectares
Demonstration or Pilot Project
Flood Risk Management
Habitat Protection
From 2014 onwards, Lymington Harbour Commissioners have carried out ‘bottom-placement’ recharge work in front of Boiler Marsh at the mouth of the Lymington Estuary. This is an alternative to placing it at a licensed offshore disposal ground.
For this recharge work, dredged material (silt) is loaded into barges by back hoe at the dredge areas (channel and mooring site in the inner Estuary). Then, the barges move to the new disposal ground and discharge the sediment by opening the hopper doors before then returning to the dredging site(s) to collect more sediment.
The aim of these campaigns is to place sediment as high up the intertidal area as is feasible, so that it has the greatest chance of either feeding the adjacent marsh or acting as a gradually eroding ‘sacrificial bund’ feature to temporarily shield this part of the inner marsh from erosion.
To help achieve these aims and to extend the amount of time that the deposited sediment remains in situ, the disposal is undertaken only on the larger high tides.
To also help with these objectives, an effort is made to place each new deposit as close as possible to, or even on top of, previous ones. This approach is also designed maximise the amount of sediment that can be placed within the deposit ground. To achieve this, the barges are guided into their deposit location by post markers. The deposition process itself lasts only a few minutes.
The results of regular bathymetric and LiDAR monitoring show that much of the sediment is remaining in situ at the placement site and there is a progressive build-up of sediment at the site.
There are losses of sediment between the winter campaigns as expected. The extent of these losses varies between years and is influenced by the composition of the sediment and the deposit location. In total, around 40,000 m³ have been placed here over the seven years From 2014 to 2021 and around half of this was still in place in early 2021.
NB THE VIDEO ON THIS PAGE DOESN'T SHOW THE BENEFICIAL USE ITSELF BUT IS A GOOD DESCRIPTION OF THE TYPICAL DREDGING AND DISPOSAL WORK AT LYMINGTON
ABPmer
Quayside Suite
Medina Chambers
Town Quay
Southampton
SO14 2AQ