Case study:Little Waltham Meadows Back Channel creation

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Location: 51° 46' 26", 0° 28' 51"
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Project overview

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Status Complete
Project web site
Themes Habitat and biodiversity, Hydromorphology
Country England
Main contact forename Kieren
Main contact surname Alexander
Main contact user ID User:KierenAlexander
Contact organisation Essex Wildlife Trust
Contact organisation web site http://www.essexwt.org.uk
Partner organisations Essex and Suffolk Water (Northumbrian Water), Chelmer and Blackwater Catchment Partnership, Natural England, Environment Agency, Chelmer and Blackwater Navigation (Essex Waterways Ltd), Parish Councils and the Rural Communities Council for Essex, Landowners and farmers, Rivers Trust, Essex County Council, Essex Farming and Wildlife Advisory Group
Parent multi-site project
This is a parent project
encompassing the following
projects
No
Project picture

Project summary

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This is a multi-benefit project aimed at improving in channel morphological diversity, reducing the amount of diffuse pollution and sedimentation entering the main river Chelmer. It will also increase the amount of riparian habitat along the River Chelmer and enhance the resilience of the wet woodland.

This project was funded by the Catchment restoration fund, as part of the Essex Healthy headwaters scheme. The earthworks were undertaken in late Summer, early Autumn 2014.

The aims of this project were achieved in the first instance by the creation of a new 280 backwater channel with three settling ponds and a sluice structure. The back channel connects with the river and an existing culvert/drainage point off the nearby main road. The ponds and back channel in the first instance allow for any nitrate and phosphate heavy water coming through the culvert to be settled and filtered. The back channel is also excellent in times of high flows at providing fish refuges, especially for fish fry which are in danger of being washed downstream in flood events. It will also provide an interface between the river and the bank side which will allow some interesting and diverse flora to develop. Finally, by connecting the river with the floodplain it creates additional riparian habitat and has a small but meaningful impact on flooding by increasing storage in the floodplain, outside of Chelmsford.

The other aim of the project, namely to increase the resilience of the wet woodland. Was created by installing a sluice at the far end of an existing ditch. Unlike the other sluice this captures rain water and holds it back on the landward side, this has been set at a level that is higher than previous levels and will effect a raise in water off approximately 50 centimeters. The increased water levels have also allowed for additional planting to be undertaken that will extend the water by over half a hectare, there has also been some limited earthworks to spread the water over a wider area.

These works will keep the woodland wetter in the summer months, keeping Bramble under control and allowing a further establishment of the flora normally associated with wet woodlands.

Monitoring surveys and results

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There has been a full pre-works survey conducted by Essex Ecological Consultancy service which has established a baseline index of key invertebrates and flora.

Post works it is hoped that this survey can repeated once the site has settled down to allow an accurate summary of the effect of the works. There will also be adhoc surveys of any flora development in time.

Lessons learnt

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The sluice at the Wet woodland presented some issues post project, with an unacceptable level of water loss through the frame. This was rectified and is now operating at a normal level. However, some thought must be given to the purpose of the sluice and this should inform the design of the sluice. Holding water back requires a strong but not particularly flexible structure.

Any back channel is relies heavily on the correct levels being established, this relies on understanding the local conditions i.e. any local impoundments this may not be easily recognized so early and often discussions with the EA or the local Drainage board are necessary.


Image gallery


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Little Waltham After.jpg
Work begins on the Back channel.jpg
The back channel comes together.jpg
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Catchment and subcatchment

Catchment

River basin district Anglian
River basin Combined Essex

Subcatchment

River name Chelmer (Upper)
Area category 10 - 100 km²
Area (km2)
Maximum altitude category 100 - 200 m
Maximum altitude (m) 124
124 m
0.124 km
12,400 cm
Dominant geology Calcareous
Ecoregion Great Britain
Dominant land cover Arable and Horticulture
Waterbody ID GB105037041200



Site

Name
WFD water body codes GB105037041200
WFD (national) typology
WFD water body name Chelmer (Upper)
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) 400
400 m
0.4 km
40,000 cm
Project started 2012/10/01
Works started 2014/09/22
Works completed 2014/11/21
Project completed 2015/03/31
Total cost category 50 - 100 k€
Total cost (k€) 90
90 k€
90,000 €
Benefit to cost ratio
Funding sources Defra Catchment Restoration Fund

Cost for project phases

Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname
Investigation and design Essex Wildlife Trust Kieren Alexander
Stakeholder engagement and communication Essex Wildlife Trust Kieren Alexander
Works and works supervision Essex Wildlife Trust Kieren Alexander
Post-project management and maintenance Essex Wildlife Trust Kieren Alexander
Monitoring Essex Wildlife Trust Kieren Alexander



Reasons for river restoration

Mitigation of a pressure
Hydromorphology Channel pattern/planform
Biology Fish, Invertebrates, Macrophytes
Physico-chemical Reduce diffuse pollution, Specific synthetic pollutants
Other reasons for the project Biodiversity, Landscape enhancement, flood alleviation


Measures

Structural measures
Bank/bed modifications New sluice structures
Floodplain / River corridor Creation of backwaters, Creation of wet woodland, Protect/restore riparian zone
Planform / Channel pattern
Other
Non-structural measures
Management interventions
Social measures (incl. engagement) Volunteer 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

Link Description
http://http://www.essexrivershub.org.uk/ For more information on this and other projects in Combined Essex catchment

Supplementary Information

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