Beneficial use of dredged sediment
Hamford Water (Essex)
Improve Flood Protection
At Horsey Island, a number of different measures were undertaken from 1998 to 2006 to protect the island’s badly deteriorating seawalls and/or to restore eroding habitats. This work was carried out by the Environment Agency in partnership with Harwich Haven Authority (HHA) and the landowner. The recharge materials were derived from capital and maintenance dredging work undertaken in the navigation approaches and ports of Harwich and Felixstowe. A recent review by ABPmer (in 2016) summarised the quite complex set of initiatives (and associated studies, evidence collation exercises and assessments) that has been carried here over several years. In simple terms the works can be distilled down to six key elements (retrospectively referred to here as Phases 1 to 6): 1) Phase 1 1988: Installation of Thames Lighter Barges to act as wave energy breaks; 2) Phase 2 Early 1990s: Importation of shingle and sand (148,000 m³) over several phases (starting with 18,000 m³ in 1990) to create a new barrier along the alignment of the lighter barges; 3) Phase 3 1992 Small-scale trial of silt recharge onto saltmarsh (<1,000 m³) undertaken at the south-east corner of the island; 4) Phase 4 1998: First major importation of silt (20,000 m³) over 2.7 ha of mudflat behind the sand and shingle barrier to raise intertidal levels, stabilise the barrier and create marsh habitat; 5) Phase 5 2001 and 2003: Second and third importation of silt in 2001 (15,750 m³) and 2003 (25,000 m³) to ‘top up’ intertidal area behind the sand and shingle barrier; 6) Phase 6 2005/06: Importation of silt (47,000 m³) over two phases in November 2005 (21,000 m³) and January 2006 (26,000 m³) on to a separate area of deteriorating saltmarsh to the west of the sand/shingle barrier to raise and restore this degraded habitat and protect the sea wall. These projects have demonstrated how coarse and fine-grained dredged sediments can be used effectively to build up and restore intertidal habitats and enhance coastal protection. They have also shown that such benefits can persist over decades (including a period which has seen major storm events) and provide a cost effective flood defence mechanism.