Description • Monitoring • Effectiveness of the scheme • Further information

Horsey Island, Hamford Water (northeast)

Description

Horsey Island (see picture below) lies within the inlet of Hamford Water and is part of the Walton Backwaters and Essex Estuaries SAC. The island is strategically important in that it provides protection against wave action to the Backwaters, thereby reducing erosion. Recharge of the foreshore was first carried out in the early 1990’s and represented the first application of dredged material for beneficial purposes in the UK. In total, a volume of 18000m³ of coarse dredged material was sprayed onto the mid intertidal area by rainbow discharge from a self-load, self-empty discharge vessel at high water on spring tides. The material was used to fill the gaps between a line of disused Thames Lighter barges that were grounded on the foreshore.

Recharge scheme at Horsey Island (Environment Agency)

Monitoring

Pre- and post-monitoring surveys were carried out to ascertain the effects of the scheme. Five replicate 10cm diameter cores were sampled before and after mud placement on the upper, middle and low shore and on an adjacent control site. As predicted, the coarser nature of the recharge material led to a complete change in the sediment character of the site. Similarly, the deposition of material led to localised changes in foreshore bathymetry and benthic invertebrate surveys showed marked changes in the community type, resulting in a switch in dominance from species associated with muds to those associated with coarser material. In particular the king ragworm, Nereis virens, was shown to significantly increase in abundance. Pollution surveys revealing no increase in sediment contaminant levels.

Generally, however, the erosion of the foreshore has been arrested and the wetland is being restored.

Effectiveness of the scheme

The Horsey Island recharge scheme is considered to be one of the most successful projects of its type carried out in the UK in terms of providing the coastal defence function for which is was designed. The abundance of the ragworm Nereis, supports a thriving Sea Bass fishery and bird populations. A new marsh habitat also formed behind the recharged material.

Further information

Ian Black
Site Manager
Colchester Office, Harbour House
Hythe Quay
Colchester
Essex
CO2 8JF
01206 796666

Environment Agency (1999). Monitoring foreshore recharge works, Essex 1998- 2002. Contract 0031: Post-placement monitoring studies. Unpublished report.