Case study:Castle Acre Rehabilitation Project

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Location: 52° 42' 0", 0° 41' 25"
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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, Natural England
This is a parent project
encompassing the following
projects
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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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: Nar SSSI project, Narborough Rehabilitation Project, River Nar Restoration Project, River Nar, Mileham River Restoration Project, West Lexham Rehabilitation Project


Site

Name Castle Acre
WFD water body codes GB105033047791
WFD (national) typology
WFD water body name Nar to confl with Blackborough Drain
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

Reach length directly affected (m) 300
300 m
0.3 km
30,000 cm
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

Mitigation of a pressure
Hydromorphology Width & depth variation
Biology
Physico-chemical
Other reasons for the project


Measures

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)
Other


Monitoring

Hydromorphological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Biological quality elements

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Physico-chemical quality elements

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Monitoring documents



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Supplementary Information

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