Medmerry Realignment Scheme

Medmerry Copyright of the Environment Agency

The above image is Copyright of The Environment Agency 2013.

Medmerry is one of the stretches of coastline most at risk of flooding in southern England. The overall scheme involves building major new sea defences inland and allowing a new intertidal area to form between Selsey and Bracklesham in West Sussex.

Salix, working as a specialist sub contractor and supplier to Team Van Oord, have created important new wildlife habitat for the endangered water vole.

In order to allow the existing shingle shoreline to be breached, large areas of water vole habitat would become inundated by sea water. Salix were tasked with creating new compensation habitat for the water voles located behind the new flood bank which was set inland. In total, over 4km of new ditches were dug and 3 hectares of reedbeds and online wetlands created.

The greatest challenge was to establish mature water vole habitat before the existing shingle defenses were breached. A Natural England license would only allow a breach if suitable compensatory water vole habitat was ready to re-home the water voles. The habitat had to be ready within 12 months in order for the breach to occur in September 2013. Salix devised a range of vegetation establishment techniques based on a priority system.

In high priority areas we translocated wetland vegetation and sediments from the existing ditch network. Vegetation from the centre of existing water vole habitat ditches was carefully removed under close supervision. The vegetation was translocated into the newly created ditch network at average water level. Each particular plant species or community of vegetation was dug at different depths, translocated and placed in the new channel differently to reflect the species specific needs.

Summary of Salix Specialist Involvement

  • Establish the maximum amount of habitat within a fixed budget
  • Focus techniques within key/priority areas
  • Limited donor sites of aquatic macrophytes for translocation with a very short time frame. Therefore pre-established Coir Pallets were used in high priority areas
  • High density wetland plug planting was required to make up the shortfall in lower priority areas where establishment of mature habitat was targeted over a longer timescale

Establishment of 3,000 metres of translocated material, supplemented with over 2,500 metres of mature Coir Pallets, has been a great success, creating 8km of new mature bank habitat within a single growing season. Natural England approved the habitat for release of water voles in July 2013 allowing the scheduled breach to occur in September 2013. The reedbed planting has established and will evolve over time to create a mature reedbed.

Coir Pallets installed April 2012Coir Pallets after installationNew ditches for water vole created using pre-established Coir Rolls and plantingCoir Pallets in August after 4 monthsCoir Rolls after 18 months creating mature water vole habitatReedbed planting after 6 weeks using pre-established Coir Pallets and plug plantsReedbed planting after 12 monthsTranslocation taking vegetation from donor site March 2012Placing translocated vegetation in the new channels March 2012Regrowth in new channel August 2012Translocation after 18 monthsWhole site aerial 19.09.13 Copyright of the Environment AgencyWater vole tagging Photo Courtesy of Rowenna Baker
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Reedbed planting after 6 weeks using pre-established Coir Pallets and plug plants

 

A number of YouTube videos show the overall scheme