Case study:Castle Acre Rehabilitation Project

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Location: 52° 41' 59.91" N, 0° 41' 24.59" E

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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	River Restoration Centre
Contact organisation web site	http://www.therrc.co.uk
Partner organisations	Environment Agency, River Restoration Centre
Parent multi-site project
This is a parent project encompassing the following projects	No

River Nar SSSI at Castle Acre

Project summary

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Work was considerable, affecting about 65% of the channel within a stretch of c300m. Work was undertaken to create greater diversity of habitat by modifying both the long and cross-sections (formation of pools and fast ‘run’ habitat); narrow the channel to improve self-cleansing of the bed and thus reduce sand and silt deposition as well as ‘weed’ growth in the future; improve the landscape quality of the area by replacing the unsightly deflectors with ‘living’ features that would do a more effective job than the deflectors were attempting to do. This section of river has more gradient than the other two sites, and this tended to recede on passing downstream. In habitat terms it primarily suffers badly from historic widening, and attempts to narrow it with deflectors have been generally ineffectual due to the inability of marginal plants to encroach and become firmly established – some deflectors have, however, established some habitat diversity.

The key to being able to carry out the works as desired was the presence of large patches of sedge (Carex acutiformis) and reed (Phalaris arundinacea). In several places the river was narrowed by over 4m simply by transferring large ‘sods’ of sedges; these imports were placed within the inside the existing bank, and will now form the new bank. In the upstream straight section to the first bend, three pools and upstream deflectors were created. As the bed of the newly created two downstream pools of this sequence (photos 2-5) had flinty-gravel present, this was sprinkled on the bed of the narrowed channel upstream to accentuate the improved speed of flow into the pools, and improve the habitat variability within the reach. Material dug from pools to form the upstream shoulders that narrowed the channel were blinded by sedge/reed from the adjacent field. These features were enlarged by further sedge/reed sods.

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Lessons learnt

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Catchment and subcatchment

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Catchment

River basin district	Anglian
River basin	North West Norfolk

Subcatchment

River name	Nar
Area category
Area (km2)
Maximum altitude category
Maximum altitude (m)
Dominant geology
Ecoregion
Dominant land cover
Waterbody ID

Site

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Name	Castle Acre
WFD water body codes
WFD (national) typology
WFD water body name
Pre-project morphology	Single channel, Impounded, 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
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

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Reach length directly affected (m)	300300 m <br />0.3 km <br />30,000 cm <br />
Project started
Works started	2011/03/01
Works completed	2011/03/31
Project completed
Total cost category
Total cost (k€)
Benefit to cost ratio
Funding sources	Environment Agency/Norfolk Rivers Internal Drainage Board

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

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Mitigation of a pressure
Hydromorphology	Width & depth variation
Biology
Physico-chemical
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Measures

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Structural measures
Bank/bed modifications	Creation of pools and riffles
Floodplain / River corridor
Planform / Channel pattern	Channel narrowing
Other
Non-structural measures
Management interventions
Social measures (incl. engagement)
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Monitoring

Hydromorphological quality elements

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quality elements

Element	When monitored		Type of monitoring		Control site used	Result
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Biological quality elements

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quality elements

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Physico-chemical quality elements

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quality elements

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Any other monitoring, e.g. social, economic

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Monitoring documents

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Image gallery

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Additional documents and videos

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River Nar Rehabilitation summary report by Nigel Holmes

Additional links and references

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Supplementary Information

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