Case study:Meander reinstatement on the River Wensum at the Ryburgh Loop

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Location: 52° 48' 11", 0° 55' 8"
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Project overview

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Status Complete
Project web site http://www.therrc.co.uk/rrc_case_studies1.php?csid=76
Themes Fisheries, Habitat and biodiversity
Country England
Main contact forename Rob
Main contact surname Dryden
Main contact user ID
Contact organisation Environment Agency
Contact organisation web site http://www.environment-agency.gov.uk
Partner organisations Wensum River Restoration Strategy
Parent multi-site project

Case_study:Wensum River Restoration Strategy

This is a parent project
encompassing the following
projects
No
The reconnected meander - the Ryburgh Loop

Project summary

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Site background The River Wensum is a chalk SSSI and SAC river currently stated as being in unfavourable condition. Located to the southeast of the Norfolk town of Fakenham the meander loop at Great Ryburgh Common was bypassed in the 1950’s when the River Wensum was straightened, widened and deepened as part of a land drainage improvement scheme.

The river restoration work undertaken involved reinstating a former meander, increasing channel sinuosity and flow diversity. The work was part of the wider River Wensum Restoration Project.

Objectives To re-instate the natural river form and function by re-connecting the old meander. It was designed so that at normal flows all the flow would go down the old meander and at high flow, part of the flow would be diverted into the straightened channel. To re-connect the old meander by removing the silt layer from the old channel whilst retaining the existing gravel substrate where it still existed.

Design The old meander was carefully excavated leaving the riverbed gravels intact where they already existed. In addition new gravels were added to create shallow glides. Deeper pools were dug to provide refuge ares for fish and other aquatic species. The existing straightened channel was plugged such that in normal flow conditions, the river flows around the re-connected meander. The straightened channel therefore acts as a flood relief channel at times of high flow and as a quiet backwater during normal flow. In addition, channel narrowing was achieved by creating a bund along the line of the new bank, and this was covered with coir matting and was planted up with live plants.

Subsequent performance – RRC’s views (2011) Eighteen months on, the site is fully vegetated and functioning well as a re-connected meander. The original gravel bed was exposed during excavation and the use of adaptive management allowed these original features to be incorporated into the on-the-ground works. The Environment Agency OPS team was used to do the works as they had experience of doing similar work(at Bintree further down the catchment). Prior to re-meandering, the channel was straightened and over-wide. The project has recreated the natural chalkstream habitat, with pool and riffle sequences. The substrate now has macrophytes growing along much of its length. By allowing high flows to pass down the old straightened channel the flood capacity has been increased, and during normal flows the old straightened channel acts as a backwater habitat.

Monitoring surveys and results

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Image gallery


Ryburgh Common pre works
Ryburgh Common pre-works
Ryburgh Common before works
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Catchment and subcatchment

Catchment

River basin district Anglian
River basin Broadland Rivers

Subcatchment

River name Wensum US Norwich
Area category 100 - 1000 km²
Area (km2)
Maximum altitude category Less than 100 m
Maximum altitude (m) 98
98 m
0.098 km
9,800 cm
Dominant geology Calcareous
Ecoregion Great Britain
Dominant land cover Arable and Horticulture
Waterbody ID GB105034055881



Other case studies in this subcatchment: Great Ryburgh End Restoration Scheme, River rehabilitation on the River Wensum at Swanton Morley, Sculthorpe Moor Restoration Scheme, Wensum River Restoration and Floodplain Enhancement, Wensum River Restoration and Floodplain Enhancement, Pensthorpe


Site

Name Ryburgh Loop
WFD water body codes GB105034055881
WFD (national) typology
WFD water body name River Wensum
Pre-project morphology
Reference morphology
Desired post project morphology
Heavily modified water body No
National/international site designation EU - Special Area of Conservation
Local/regional site designations UK - Site of Special Scientific Interest
Protected species present Yes
Invasive species present No
Species of interest
Dominant hydrology
Dominant substrate
River corridor land use 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) 600
600 m
0.6 km
60,000 cm
Project started 2010/10/01
Works started
Works completed
Project completed 2010/12/31
Total cost category 1 - 10 k€
Total cost (k€) 10.5
10.5 k€
10,500 €
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

Supplementary funding information

paid in pound 105,000



Reasons for river restoration

Mitigation of a pressure
Hydromorphology Channel pattern/planform
Biology
Physico-chemical
Other reasons for the project


Measures

Structural measures
Bank/bed modifications
Floodplain / River corridor
Planform / Channel pattern Reconnection of cutoff meander
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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Additional links and references

Link Description
http://www.therrc.co.uk/rrc case studies1.php?csid=76 RRC case study

Supplementary Information

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