Case study:Chelmer Valley Local Nature Reserve

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Location: 51° 44' 41", 0° 28' 26"
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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 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 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 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

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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.


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Catchment and subcatchment



Site

Name Chelmer
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

Reach length directly affected (m)
Project started
Works started
Works completed
Project completed
Total cost category
Total cost (k€) £25k
"£" is not declared as a valid unit of measurement for this property.
Benefit to cost ratio
Funding sources Catchment Partnership Action Fund

Cost for project phases

Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname
Investigation and design more than 10000 k€ 25000
25,000 k€
25,000,000 €
Stakeholder engagement and communication
Works and works supervision
Post-project management and maintenance
Monitoring



Reasons for river restoration

Mitigation of a pressure Flood risk management
Hydromorphology
Biology
Physico-chemical
Other reasons for the project


Measures

Structural measures
Bank/bed modifications Creation of berms
Floodplain / River corridor Lowering of embankments, Floodplain reconnection, Riparian habitat restoration
Planform / Channel pattern
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

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

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

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


Monitoring documents



Additional documents and videos


Additional links and references

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Supplementary Information

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