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, 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 Select a catchment/subcatchment Edit the catchment and subcatchment details (affects all case studies in this 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) 9595 m <br />0.095 km <br />9,500 cm <br /> 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 Castle Acre Common WEG project, River Nar Restoration Project, River Nar, Mileham River Restoration Project, West Lexham Rehabilitation Project Site Edit 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 Edit project background 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 Edit reasons for restoration Mitigation of a pressure Hydromorphology Width & depth variation Biology Physico-chemical Other reasons for the project Measures Edit 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 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 River Nar Rehabilitation summary report by Nigel Holmes Additional links and references Edit links and references Link Description Supplementary Information Edit Supplementary Information