Case study:River Witham Great Ponton

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Location: 52° 51' 32.39" N, 0° 37' 4.63" W

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Project overview

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Status	Complete
Project web site
Themes	Habitat and biodiversity
Country	England
Main contact forename	Matt
Main contact surname	Parr
Main contact user ID
Contact organisation	Environment Agency
Contact organisation web site	http://www.gov.uk/government/organisations/environment-agency
Partner organisations	Wild Trout Trust and Grantham Angling Association Fly Fishing Section
Parent multi-site project	Upper Witham Restoration
This is a parent project encompassing the following projects	No

By-pass channel under construction.

Project summary

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Channel narrowing and flow deflection to create flow variation and beneficial bed scour using a variety of techniques: log flow deflectors (vanes), open and enclosed log/faggot and brushwood mattresses (silt-traps); increasing in-stream woody habitat by securing existing deadwood and hinging and pinning (layering) live riverside trees; creation of sections of 2-stage channel and enhancing marginal wetland habitat by excavating of bays/berms; and the reduction of sediment inputs by ford refurbishment and riverside fencing. The final phase involved major works to restore a section of the river to a more natural planform.

Project Objectives The initial downstream phases were primarily designed to

Stabilise eroding river banks to reduce sediment inputs caused by fluvial processes and livestock.
Trap mobile fine sediments already in the river.
Improve conveyance during higher flows and reduce flood risk.
Improve in-stream habitats for fish and invertebrates, including white-clawed crayfish.

The final phase, at Grange Farm, set out to restore a degraded section of the river to its original course, such that the naturalised section of river would function in an ecologically and geomorphologically improved form.

Monitoring surveys and results

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For all phases, visual inspections and regular fixed-point photographs are being undertaken to monitor the integrity and performance of the enhancement works and record any changes they are making to river morphology. Specific to Phase 2, modifications to the channel profile as a result of the woody material introduction upstream of Dunkirk Cottage can be determined by comparison with a baseline cross-section in this location and the effects on turbidity and invertebrate populations will also be monitored here. For phase 3, in addition to an annual redd (trout spawning “nest”) survey of the new riffles, the established annual fish monitoring downstream of Easton Walled Garden and invertebrate sampling at Easton Lane Bridge will be used to detect any changes as a result of the works.

Lessons learnt

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The importance of gravel and floodplain connectivity to drive significant change. Need for wood in by-pass channel. Where the constraints have been addressed by realigning and re-naturalising the channel at Grange Farm, habitat improvement has been more successful, although further intervention is required. Introduced gravel has been displaced in high flows and needs to be replaced with larger calibre material which will remain stable and restore the designed pool-riffle sequence. The abrupt change in valley floor gradient at this site constrained the design of the new channel and caused this situation; this is unusual and should not be a deterrent to similar river restoration schemes elsewhere.

Image gallery

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Catchment and subcatchment Select a catchment/subcatchment Edit the catchment and subcatchment details (affects all case studies in this subcatchment) Site Edit site Name River Witham Great Ponton WFD water body codes GB105030051570 WFD (national) typology WFD water body name Upper Witham Headwater to confluence Cringle Brook Pre-project morphology Reference morphology 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 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) 2.72.7 m <br />0.0027 km <br />270 cm <br /> Project started 01/02/2013 Works started Works completed Project completed Total cost category Total cost (k€) 141141 k€ <br />141,000 € <br /> Benefit to cost ratio Funding sources EA 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 Land Drainage Hydromorphology Biology Fish Physico-chemical Phosphates Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Tree Hinging, Faggot Mattresses, Flow Deflectors Floodplain / River corridor Fencing, cattle access points Planform / Channel pattern Weir Bypass, new meandering channel planform 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 Project Case Study Additional links and references Edit links and references Link Description Supplementary Information Edit Supplementary Information