Case study:Narborough Rehabilitation Project

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Location: 52° 41' 16", 0° 34' 41"
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Project overview

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Status Complete
Project web site
Themes Habitat and biodiversity
Country England
Main contact forename Nigel T.H.
Main contact surname Holmes
Main contact user ID
Contact organisation
Contact organisation web site
Partner organisations Environment Agency, River Restoration Centre, Natural England
Parent multi-site project
This is a parent project
encompassing the following
projects
No
just post works

Project summary

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River excavations and modifications took three days, the majority of one of these being import of the gravel to the ‘runs’.

Work was implemented in c1km of river. There was absolutely no gradient within the sections modified, with the river being deep and sluggish throughout. Work carried out:

    • created greater diversity of habitat by modifying both the long and cross-sections;
    • locally narrowed the channel to improve self-cleansing of the bed in these locations, and accelerated flow into pools created immediately downstream;
    • removed the unsightly deflectors by replacing them with ‘living’ features that already are doing a much more effective job than the deflectors were attempting to do;
    • the one main difference from the Castle Acre stretch was that some of the upstream ‘runs’ had a thin layer of gravel spread over them too.

Differences in character were primarily determined by the character of the river bed where pools were excavated, and the extent of reed/sedge available from adjacent to the river to add to the channel.

Where the bed was hard, and reed/sedge was plentiful, upstream narrowing could be more extensive. In all cases where the bed was hard (predominantly chalky clay), very distinct pools and upstream ‘runs’ were formed. Where-ever possible the bed of the narrowed channel upstream of the pools was shallowed by adding material dug from the pools – this could only be done where flints or firm clay formed the substrate.

Where the bed was pure soft peat, the distinction between the narrowed channel upstream, and the deepened channel downstream, was much less. Had deflectors not already been present in the channel, it would have been difficult, or impossible, to establish narrowing upstream......the deflectors now form the downstream edges of the shoulders. Without reeds/sedge from adjacent to the river being added to these areas, they could not have been expected to be retained in the long term.

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Lessons learnt

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Catchment and subcatchment

Catchment

River basin district Anglian
River basin North West Norfolk

Subcatchment

River name Nar to confl with Blackborough Drain
Area category 100 - 1000 km²
Area (km2)
Maximum altitude category Less than 100 m
Maximum altitude (m) 95
95 m
0.095 km
9,500 cm
Dominant geology Calcareous
Ecoregion Great Britain
Dominant land cover Arable and Horticulture
Waterbody ID GB105033047791



Other case studies in this subcatchment: Castle Acre Rehabilitation Project, Nar SSSI project, River Nar Restoration Project, River Nar, Mileham River Restoration Project, West Lexham Rehabilitation Project


Site

Name Narborough
WFD water body codes GB105033047791
WFD (national) typology
WFD water body name Nar to confl with Blackborough Drain
Pre-project morphology Single channel, Straightened
Reference morphology Single channel, Pool-riffle, Sinuous
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
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Average bankfull channel width (m)
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Average bankfull channel depth (m)
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Average channel gradient
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Project background

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Reasons for river restoration

Mitigation of a pressure
Hydromorphology
Biology
Physico-chemical
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Measures

Structural measures
Bank/bed modifications
Floodplain / River corridor
Planform / Channel pattern
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Non-structural measures
Management interventions
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Monitoring

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