Case study:Chelmer Valley Local Nature Reserve

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Location: 51° 44' 41.26" N, 0° 28' 26.23" E

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Project overview

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Status	Complete
Project web site	http://www.therrc.co.uk/sites/default/files/projects/6_chelmer.pdf
Themes	Flood risk management, Habitat and biodiversity, Hydromorphology, Social benefits, Water quality
Country	England
Main contact forename	Trev
Main contact surname	Bond
Main contact user ID
Contact organisation	Environment Agency
Contact organisation web site
Partner organisations	Essex Wildlife Trust
Parent multi-site project
This is a parent project encompassing the following projects	No

Project picture

Project summary

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Restoration of the River Chelmer upstream of Chelmsford City Centre by re-profiling the banks to increase in-channel morphological diversity, create additional marginal aquatic habitats, improve floodplain connectivity and create additional backwater habitats. The River Chelmer has historically been heavily modified to improve flood protection and land drainage. This has led to a uniform wide, straight, deep channel upstream of Chelmsford City Centre. This in tern has resulted in reduced plant diversity, and there has recently been deterioration in fish status. The Chelmer Valley Local Nature Reserve (LNR) is a much loved open space situated to the north of Chelmsford city centre (Map 1). Approximately 2.5km long, the Chelmer Valley LNR consists of parkland, green spaces, unimproved grassland, ponds, wet margins, riparian woodland and the River Chelmer itself (Photo 1). As part of this project, informal embankments created through years of dredging were lowered and the won material was used within the river to construct earth berms. This improved floodplain connectivity, created marginal habitat for plants and restricted the width of the active river channel, encouraging geomorphic processes. In addition, flood risk modelling of the scheme has shown flood risk benefits emerging from the project during particular flood frequencies. Flood risk modelling indicated that the scheme would lead to a small, net decrease in lateral flood extent during both 10% and 1% annual exceedance probability (AEP) events. Modelling also suggests reduced flood depths of up to 0.3m in some locations during a 10% AEP event and reduced flood depths of 0.15m in some locations during a 1% AEP. The reduced flood risk is believed to be due to the improved connectivity between the main river channel and the floodplain, which means water evacuates onto the floodplain earlier and the flood peak is marginally reduced.

Monitoring surveys and results

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Increasing the diversity of the channel provide different habitats to support a wider diversity of plants and animals. Fish bays provide shallow, slower flowing, warmer water preferred by small fish and fry. Blackwater habitats increase habitat diversity, whilst providing a refuge for fish and invertebrates from high flows. The banks and channel of the main river were re-profiled at 9 locations. The river bank was lowered to re-connect the river to its natural floodplain, improving marginal and riparian wetland habitats. Improving connectivity between the river and floodplain allows sediment to settle out on the floodplain, and fish and invertebrates to escape from the highest flows in flood events By storing water on the floodplain sooner, downstream flood risk can also be reduced. The bank material was pushed into the channel, creating earth berms. These narrow the channel during low flows, increasing water velocity. This helps other river processes such as sediment transfer, erosion and depositing and oxygenation of the water, which creates habitats and improves water quality. The berms also create diversity of marginal and aquatic habitats, which was previously very uniform. In addition, shallow bays were created and a backwater improved to provide additional habitat for fish and fry.

Lessons learnt

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Early communication with permitting bodies and involvement of local communities is essential to deliver successful projects in a short timescale.

Image gallery

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Catchment and subcatchment Select a catchment/subcatchment Site Edit site Name WFD water body codes GB105037033950 WFD (national) typology WFD water body name Pre-project morphology Reference morphology 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 Works started Works completed Project completed 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 more than 10000 k€ 2500025,000 k€ <br />25,000,000 € <br /> 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 Additional links and references Edit links and references Link Description Supplementary Information Edit Supplementary Information