Case study:Manthorpe Floodplain Reconnection

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Location: 52° 55' 44.86" N, 0° 37' 44.24" W

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Project overview

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Status	Complete
Project web site
Themes	Flood risk management, Habitat and biodiversity
Country	England
Main contact forename	Matt
Main contact surname	Parr
Main contact user ID
Contact organisation	Enviroment Agency
Contact organisation web site	http://www.gov.uk/government/organisations/environment-agency
Partner organisations	Wild Trout Trust, Lincolnshire Wildlife Trust.
Parent multi-site project	Upper Witham Restoration
This is a parent project encompassing the following projects	No

Project after completion.

Project summary

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There were five components to the scheme:

• Removal of redundant flood bank, and lowering of the floodplain to create a terraced floodplain with a lower more frequently connected floodplain and a higher terrace of un-lowered floodplain. This gives maximum benefit to the river and natural processes whilst providing some variation in flood event storage and habitat evolution and variety.

• Addition of riffles and gravel supply in the form of point bars and islands and splitting of channel into multiple threads creating a more natural form and allowing the river space to adjust to changes in flow but also allow natural processes like silt deposition, channel evolution, less intensive management, woody material to be retained in channel and on flood plain. The gravel raises the bed helping to connect the river into the floodplain reducing the amount of spoil generated to lower floodplain as well as providing rich habitats for riverine wildlife.

• Creation of floodplain ponds and terrestrial habitat features like habitat piles, stone piles for hibernacular, and woody material on the floodplain to encourage further hydraulic roughness in high flow events

• Spreading of spoil over the top of the valley sides outside of the floodplain, this was then reseeded with appropriate wildflower grassland mix and provides pollinator benefits.

Monitoring surveys and results

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Brown trout have already been observed spawning on the new limestone gravels. Crayfish monitoring was carried out pre works and showed a very low baseline population with only 6 individuals caught, repeat monitoring of this will be carried out along with repeat bird surveys of the site.

Lessons learnt

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4200 m3 of earth was removed from the floodplain during the lowering and removal of embankments. Reconnecting the floodplain has created 19,500m3 of space for water which now reconnects to the lower floodplain frequently after intense rainfall events at a 1 in 2 event magnitude.

Image gallery

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New channel evolving.

Catchment and subcatchment Select a catchment/subcatchment Site Edit site Name WFD water body codes WFD (national) typology WFD water body name Pre-project morphology Reference morphology Desired post project morphology Heavily modified water body National/international site designation Local/regional site designations Protected species present Invasive species present Species of interest Dominant hydrology Dominant substrate River corridor land use 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 Edit project background Reach length directly affected (m) Project started Works started Works completed Project completed Total cost category Total cost (k€) Benefit to cost ratio Funding sources 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 Post-project management and maintenance Monitoring Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Hydromorphology Biology Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Floodplain / River corridor Planform / Channel pattern Other Non-structural measures Management interventions Social measures (incl. engagement) Other Monitoring Hydromorphological quality elements Edit Hydromorphological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Biological quality elements Edit biological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Physico-chemical quality elements Edit 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 Edit Other responses Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Monitoring documents Upload monitoring documents Additional documents and videos Upload additional documents Additional links and references Edit links and references Link Description Supplementary Information Edit Supplementary Information