Case study:Chelmer Valley Local Nature Reserve
Project overview
| 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 | http://www.gov.uk/government/organisations/environment-agency |
| Partner organisations | Essex Wildlife Trust |
| Parent multi-site project | |
| This is a parent project encompassing the following projects |
No |
Project summary
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 on project webpage). 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
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
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
Site
Project background
Cost for project phases
Reasons for river restoration
Measures
MonitoringHydromorphological quality elements
Biological quality elements
Physico-chemical quality elements
Any other monitoring, e.g. social, economic
Monitoring documents
Additional documents and videos
Additional links and references
Supplementary InformationEdit Supplementary Information
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