Case study:Long Eau (Great Eau)

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Location: 53° 21' 23", 0° 6' 55"
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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 Lincolnshire Chalk Streams
Contact organisation web site http://www.lincswolds.org.uk/chalk-streams/lincolnshire-chalk-streams
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

Catchment

River basin district Anglian
River basin Witham

Subcatchment

River name Long Eau
Area category 10 - 100 km²
Area (km2)
Maximum altitude category 100 - 200 m
Maximum altitude (m) 110
110 m
0.11 km
11,000 cm
Dominant geology Calcareous
Ecoregion Great Britain
Dominant land cover Arable and Horticulture
Waterbody ID GB105029061670



Site

Name Long Eau at Manby
WFD water body codes GB105029061670
WFD (national) typology
WFD water body name Long Eau
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

Reach length directly affected (m) 900
900 m
0.9 km
90,000 cm
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

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


Measures

Structural measures
Bank/bed modifications
Floodplain / River corridor Displacement of flood defences, Lowering of embankments
Planform / Channel pattern Creation of backwater
Other
Non-structural measures
Management interventions
Social measures (incl. engagement)
Other


Monitoring

Hydromorphological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Biological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Physico-chemical quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Any other monitoring, e.g. social, economic

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative


Monitoring documents



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Supplementary Information

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