Beneficial use of dredged sediment
Hamford Water (Essex)
Improve Flood Protection
At Horsey Island, a range of different projects were done between 1998 and 2021, to protect the island’s badly deteriorating seawalls and/or to restore eroding habitats. These were implemented by the Environment Agency and the RSPB, in partnership with Harwich Haven Authority (HHA) and the landowner, using sediment from capital and maintenance dredging work at the ports of Harwich and Felixstowe.
A review by ABPmer (in 2016) summarised the quite complex set of initiatives (and associated studies, evidence collation exercises and assessments) carried out from 1998 to 2006. These were divided into six separate 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.
In the years that followed this work, the barrier became the most important place for nesting little terns in Essex. It held 100% of all Essex nests in 2019 (33 pairs; 11 young fledged). This is in addition to protecting this wave-exposed corner of the island.
Then in 2020, the RSPB received MMO marine licence consent for a new Horsey Island recharge proposal. This project was implemented in October 2021 (SEE VIDEO LINK). For this campaign around 50,000 m³ of sand and gravel were used to further raise and recharge the barrier and make it more sustainable.
These projects show how coarse and fine-grained dredged sediments can be used to build up and restore intertidal habitats and enhance coastal protection. They also show that such benefits can persist over decades (including a period which has seen major storm events).