Case study:Long Eau (Great Eau)
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Project overview
| 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 |
Project summary
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.
Monitoring surveys and results
Lessons learnt
Catchment and subcatchment
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(affects all case studies in this subcatchment)
Site
| 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
| 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
| 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 | 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
| 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
Image gallery
Additional documents and videos
Additional links and references
| Link | Description |
|---|
Supplementary Information
Edit Supplementary Information