Case study:Little Waltham Meadows Back Channel creation

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Location: 51° 46' 26.36" N, 0° 28' 50.59" E

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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
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.

This 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.

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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 Combined Essex Subcatchment River name Chelmer (Upper) Area category 10 - 100 km² Area (km2) Maximum altitude category 100 - 200 m Maximum altitude (m) 124124 m <br />0.124 km <br />12,400 cm <br /> Dominant geology Calcareous Ecoregion Great Britain Dominant land cover Arable and Horticulture Waterbody ID GB105037041200 Site Edit site Name WFD water body codes WFD (national) typology WFD water body name Pre-project morphology Reference morphology Desired post project morphology Heavily modified water body National/international site designation Local/regional site designations Protected species present Invasive species present 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) 400400 m <br />0.4 km <br />40,000 cm <br /> Project started 2012/10/01 Works started 2014/09/22 Works completed 2014/11/21 Project completed 2015/03/31 Total cost category Total cost (k€) Benefit to cost ratio Funding sources 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 Works and works supervision Post-project management and maintenance Monitoring Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Hydromorphology Reduce diffuse pollution Biology Physico-chemical Other reasons for the project Biodiversity, Landscape enhancement, flood alleviation Measures Edit Measures Structural measures Bank/bed modifications New sluice structures Floodplain / River corridor Creation of backwaters, Creation of wet woodland, Riparian enhancement Planform / Channel pattern Other Non-structural measures Management interventions Social measures (incl. engagement) Local volunteers planted the trees and learnt about Natural Flood Management 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