Case study:West Lexham Rehabilitation Project

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Location: 52° 43' 9.81" N, 0° 43' 14.84" 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
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Partner organisations	River Restoration Centre, Environment Agency, Norfolk County Council, Natural England
This is a parent project encompassing the following projects

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Project summary

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A half day work to remove the impounding influence of a weir, and in the channel upstream four pools and runs were dug. A second weir, between two bridges c35m downstream of the one shown in the images, was also removed. This structure had minimal impact on habitat, but was an impediment to easy migration of fish etc. wishing pass upstream.

The structure within the meadow that was impounding the Nar upstream had some archaeological interest. For this reason there was a ‘watching brief’ from Norfolk County Council to ensure there was no damage done to any known existing interest features, and to record anything else of interest should this be revealed during the removal of the impounding structure. To minimise damage to the historical elements of the bridge, the concrete ‘boards’ were removed with great care, leaving the central pillar and upper lintel in place, yet drawing the bed down to the required level.

The effect of centuries of impoundment has been to create a sluggish/non-existent flow in the river upstream with the resultant deposition of thick layers of mud. Pools were created by widening the channel locally. To help keep the pools clear in the future, the channel was narrowed upstream. Due to the extreme depth of soft mud, narrowing was achieved by pushing in one side of the existing river edge with the back of the bucket, and the void created behind this was filled with the arisings from creating the pools. Four pools and upstream ‘runs’ were created, with the run formed upstream of the second pool from the top having a small amount of gravel spread on the bed – this was won from the bed of the river in the pool downstream.

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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 Area category Area (km2) Maximum altitude category Maximum altitude (m) Dominant geology Ecoregion Dominant land cover Waterbody ID Site Edit site Name West Lexham 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 Edit project background Reach length directly affected (m) Project started 2011/02/28 Works started Works completed Project completed 2011/03/04 Total cost category Total cost (k€) 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 Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Hydromorphology Biology Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Floodplain / River corridor Planform / Channel pattern 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