Case study:Long Eau (Great Eau)

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Location: 53° 21' 22.58" N, 0° 6' 55.08" E

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Project overview

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Status	Complete
Project web site
Themes	Flood risk management, Habitat and biodiversity, Land use management - agriculture
Country	England
Main contact forename	Nick
Main contact surname	Elbourne
Main contact user ID
Contact organisation
Contact organisation web site
Partner organisations
Parent multi-site project
This is a parent project encompassing the following projects	No

Long Eau floodplain 2005

Project summary

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Flowing from the Lincolnshire Wolds to the North Sea, the Long Eau drains a small catchment of 22.3 km2, but together with the Great Eau has a catchment area of 112.3 km2. Before restoration, the river had become embanked and channelised to protect adjacent agricultural land from flooding. The flood banks were steeply sloped directly into the channel. Dredging and removal of bankside vegetation was part of the maintenance regime, which had removed morphological features, in channel habitats and natural substrate. Historically the Long Eau had a history of washlands, regularly flooding the land adjacent to the river. Three sites were chosen along the Little ands Great Eau to demonstrate the relocation of flood banks and the provision of flood storage areas on neighbouring land. A secondary objective was to enhance habitats. An environmental stewardship scheme offered a ten year grant scheme to farmers/landowners, some of whom were already supportive of the idea of nature conservation. Long Eau at Manby- Left floodbank was lowered to just above ground level. The adjacent field was widened and flattened to act as an over spill area (1 in 10 slope). Material generated from embankment removal was used to infill and Internal Drainage Board drain which ran through flood storage area. This drain was re located behind the new embankment to maintain land drainage. The new embankment slopes were 3:1 to a height of 2.5-2.7 meters. Ledges and berms were created along the channel to increased habitat potential. Performance 1995-2001- Since completion flood protection has increased, as water spills onto new floodplain when channel reaches 2.6m or above. Below this level 75% of floodplain will retain water up to 0.5m for up to 4 months. This provides an important habitat for wetland birds. Lapwing and redshank have bred at the site. The Environment Agency estimates a saving of £400-500 a year on the previous maintenance regime.

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Catchment and subcatchment

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Site

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Name	Long Eau at Manby
WFD water body codes
WFD (national) typology
WFD water body name
Pre-project morphology	Embanked, Over-widened, Over deepened
Reference morphology	Set back defence
Desired post project morphology
Heavily modified water body	No
National/international site designation
Local/regional site designations
Protected species present	No
Invasive species present	No
Species of interest
Dominant hydrology	Artificially regulated
Dominant substrate
River corridor land use	Intensive agriculture (arable), Improved/semi-improved grassland/pasture
Average bankfull channel width category
Average bankfull channel width (m)
Average bankfull channel depth category
Average bankfull channel depth (m)
Mean discharge category
Mean annual discharge (m3/s)
Average channel gradient category
Average channel gradient
Average unit stream power (W/m2)

Project background

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Reach length directly affected (m)	900900 m <br />0.9 km <br />90,000 cm <br />
Project started	1992
Works started	1995/05/01
Works completed	1995/07/01
Project completed	1996/01/01
Total cost category	50 - 100 k€
Total cost (k€)
Benefit to cost ratio
Funding sources	environmental stewardship scheme

Cost for project phases

Phase	cost category	cost exact (k€)	Lead organisation	Contact forename	Contact surname
Investigation and design
Stakeholder engagement and communication
Works and works supervision	50 - 100 k€
Post-project management and maintenance
Monitoring

Reasons for river restoration

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Mitigation of a pressure	Flood risk management
Hydromorphology
Biology
Physico-chemical
Other reasons for the project	secondary objective of habitat improvement

Measures

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Structural measures
Bank/bed modifications
Floodplain / River corridor	setback flood defences
Planform / Channel pattern	Backwaters created
Other	Embankments lowered
Non-structural measures
Management interventions
Social measures (incl. engagement)
Other

Monitoring

Hydromorphological quality elements

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quality elements

Element	When monitored		Type of monitoring		Control site used	Result
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quality elements

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Physico-chemical quality elements

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quality elements

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Any other monitoring, e.g. social, economic

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Monitoring documents

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Additional links and references

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Supplementary Information

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