Description • Monitoring • Effectiveness of the scheme • Further information

Abbotts Hall Farm, Salcott Estuary

Description

Abbotts Hall farm is situated on the northern bank of the Salcott estuary, a tributary of the Blackwater estuary in Essex . The managed realignment scheme developed from a regulated tidal exchange scheme initiated in April 1996. Abbotts Hall is an 80ha site and was purchased in 2001 with the assistance of the following: a legacy from the late Joan Elliot, Trust Members, WWF, English Nature, Environment Agency and the Heritage Lottery Fund. It represents a multifunctional flood management scheme incorporating ecological, compensatory habitat creation, conservation, flood defence and economic functions.

Abbots Hall Farm, before breach and after breach (Environment Agency)

The scheme involved breaching the existing defences at 5 strategic locations in September 2002 to create intertidal mudflats, saltmarsh and saline lagoons and also freshwater, brackish water and grazing marsh habitats. No new defences were created as the naturally higher ground behind provided an adequate secondary defence. However, two small walls were constructed at the edges of the site to protect adjoining sites from saline intrusion. The largest breach was taken down to 1.65m ODN, enabling it to act as a sill at the end of the receding tide and to reduce the amount of sediment “stirred up” near low water on the adjacent mudflat and, thereby, reduce the suspended sediment levels potentially arriving at the oysterbeds downstream.

The site has a natural creek system and sloping topography suitable for saltmarsh development; the 3-4m contour is reached on high spring tides, and mud and silt is deposited with every tide, successfully contributing to saltmarsh and mudflat development.

Monitoring

Baseline monitoring began in the autumn of 2000 in anticipation of breaching taking place in 2001. Due to delays in acquiring the necessary permits and the outbreak of Foot and Mouth disease, breaching did not occur until 2002. Consequently, baseline monitoring continued for a further year, giving two years of pre-breach data.

The program of monitoring work involved the following:

• Hydrographic parameters (tides, waves, currents and suspended solids).
• Bathymetry.
• Bed sediment characteristics.
• Scour monitoring.
• Meteorological data.
• Bird counts.
• Macroinvertebrate counts.

Effectiveness of the scheme

No major hydrodynamic changes have been observed in Salcottt Channel in the period immediately following breaching of the sea defences; this being the time when such changes would be expected to be most apparent were they to have occurred. By spring 2003 the site had become colonised by several pioneer saltmarsh species and over 10 different species of fish were using the site. On one occasion, approximately 2,000 Herring/Sprat were caught using a seine net in one tidal pool, some of which are commercially fished. Ongoing monitoring by the Environment Agency continues.

Further information

Dave Smart Farm Warden Abbots Hall Farm Maldon Road Essex, Great Wigborough Essex CO5 7RZ

Carol Reid Conservation Officer English Nature Hertfordshire & London Team Colchester Office, Harbour House Hythe Quay Colchester CO2 8JF

Environment Agency (2003). Sustainable Flood Defences – Monitoring of the Managed Realignment Scheme at Abbots Hall, Essex. Unpublished report.