Case study:Saving Chiswick Eyot

Project overview

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Status	In progress
Project web site	http://www.savingchiswickeyot.com
Themes	Economic aspects, Environmental flows and water resources, Estuary, Fisheries, Flood risk management, Habitat and biodiversity, Hydromorphology, Land use management - forestry, Monitoring, Social benefits, Urban, Water quality
Country	England
Main contact forename	Martin
Main contact surname	Richardson
Main contact user ID	User:Mobilitydream
Contact organisation	Natural History Museum
Contact organisation web site	http://www.royalholloway.ac.uk/
Partner organisations	DHI, Fullers Brewery, Imperial College London., MOLA, Port of London Authority, Royal Holloway University of London, University of Leicester, Thames21, Thames Tideway, The British Geological Survey
This is a parent project encompassing the following projects

Surface of the Eyot showing features and elevation

Project summary

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Project team

• Martin Richardson, PhD student RHUL & NHM.
• Therese Tobin, Old Chiswick Protection Society, OCPS.
• Thames21.
• Dr. Chris Vane, British Geological Survey.
• Dr. Jamie Standing, Imperial College, University of London.
• Heena Sheth, MSc. student Imperial College University of London.

Site Designations

Old Chiswick Conservation Area, London Borough of Hounslow, 1969; Metropolitan Green Belt; Site of Metropolitan Importance for Nature Conservation, Greater London Authority (GLA),1990; Local Nature Reserve, London Borough of Hounslow, 1993; London Basin Natural Area, 1997; Strategic Nature Conservation Site, London Borough of Hounslow,1999;

Selection of Reports

1990 Chiswick Eyot, The London Ecology Unit; 1996 The Chinese mitten crab in the Thames Catchment, Environment Agency, Thomas and Yeomans; 1998 Effects of burrowing Chinese mitten Crabs (Eriocheir sinensis) on the Thames Tideway Dutton & Conroy, Environment Agency; 1999 Erosion assessment using flags, BSc. Dissertation, University of Westminster; 1999 MSc. Thesis: Burrow distribution of the Chinese mitten crab (Eriocheir sinensis) at Syon park flood meadow (SSSI), Zucco, UCL; 2000 Chiswick Eyot, River Thames, London Borough of Hounslow. A foreshore earthwork survey, Museum of London Archaeology; 2000 Chiswick Eyot Management plan 2001-2005, London Borough of Hounslow; 2002 Survey of Chiswick Eyot,Thames explorer trust; 2011 Chiswick Eyot Habitat Management Plan,Thames21; 2013 Chiswick Eyot Local Nature Reserve report, Ecology Department, Carillion integrated Services

Description

Island habitat in the Thames is rare and several, as with the lost rivers of the Thames catchment, have been degraded over time, all are now threatened by rising sea-levels. Indeed at one point there may have been more, small eyots which have now disappeared. Chiswick Eyot is a historically important island close by Chiswick Mall. What was, before the introduction of plastics, an economically important willow holt of several hundred trees has been maintained since the middle ages. Husbandry has lapsed at times with the island showing periods of low growth particularly when the area became industrialised with heavy barge traffic, gravel pits at Barnes and the Thonycroft shipyard at Chiswick for example. Later, a survey by Dr Oliver Natelson conducted in 2002 found 554 living and 319 dead trees. However, the OCPS has managed and funded annual pollarding of the willows since the 1950's. A complete biological survey funded by Defra, Thames Water and the OCPS, was carried out by Brian Wurzell and others for the Thames Explorer Trust in 2001-2002 as a follow-up to a previous survey by the London Ecology Unit in 1990.

Erosion first became a concern in the mid-1940's when it was realised that the surface area had declined by nearly 40%. Both ends of the island had receded and overall length decreased by nearly '100 yds.' Restoration work has continued since that time and several ecological studies have been conducted by the Environment Agency, Hounslow Council, and the Thames Explorer Trust. We are working with an ‘ecosystem’ of partners to address the problem of maintaining the island employing best practice techniques. Restoration work is being conducted by Thames21 and a variety of survey techniques are being used to understand processes affecting the island. An initial 3D scan of almost the entire eyot was conducted in 2016 in association with the University of Leicester and Leica Geosystems. The scan was repeated in 2017. Analysis of the data will provide greater understanding of the processes at work and enable visualisation of any changes occurring as well as determination of the rate of erosion. In addition, several hundred digital photographs were taken of areas of particular interest over a 3-year period to provide a visual record, these will also be used to develop point clouds as supplementary data.

Bi-monthly conventional topographic surveys of part of one bank were undertaken by MoLA in 1999 and 2000 allowing for decadal scale assessment of the erosion. High resolution aerial photographs and digitized historical Ordnance Survey maps are available dating back to at least the 1930s and these will be used to assess changes in surface area and any migration of the banks generally. We have engaged with the local community and formed partnerships with other commercial, charitable, academic and volunteer organisations including Thames21, the River Restoration Centre, Leica Geosystems, DHI, MoLA, and Royal Holloway University of London.

Monitoring surveys and results

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Very accurate baseline surveys have been completed. Preliminary assessment indicates a current rate of retreat of the banks at around 1m per decade, or approximately 10cm annually. A large amount of material has accumulated behind the spiling and facines which are being well maintained. Additional work, installation of supporting posts and fascines, has commenced on the east side of the island.

Lessons learnt

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Restoration work using traditional willow withies has resulted in improved overall appearance and accretion to some areas of the bank. Vegetation is not growing in the silt perhaps because of a lack of oxygen. Seepage from the bank toe area is keeping the silt mobile in some areas. The current approach employed by Thames21 of incremental maintenance appears to be successful and demonstrates good cost vs. benefit, especially since partners have started to make contributions towards costs. Withies planted on the flat surface of the island by the Old Chiswick Protection Society are growing well and the willow holt, which is pollarded annually, appears to be in good condition. The withies produced by the pollarding are bundled by the OCPS and volunteers and used to provide structure behind the spiling and fascines.

It might be useful at this point to consider additional techniques such as rolls of rocks (rocks bundled into mesh 'socks') at the areas of the bank toe with seepage. Thames21 has also mentioned using different species of aquatic plants.

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Location: 51° 29' 15.00" N, 0° 14' 45.00" W

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Image gallery

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Old Chiswick Conservation Area. London borough of Hounslow

Thames21 volunteer poster

Environment Agency flood risk level around the island

Flatness of the island surface or plateau

Volume calculation using 5m contour

Bathymetry and scans combined

3-dimensional model of the west bank

Historical records of burrowing animal species in the Thames tideway

New work in 2018 to the east side

Photo capture using remote cameras

File:Soil sampling

Jamie Standing and Dave Morritt collecting cores

Catchment and subcatchment Select a catchment/subcatchment Edit the catchment and subcatchment details (affects all case studies in this subcatchment) Catchment River basin district Thames River basin London Subcatchment River name Thames Middle Area category Less than 10 km² Area (km2) Maximum altitude category Maximum altitude (m) Dominant geology Ecoregion Great Britain Dominant land cover Urban Waterbody ID GB530603911402 Other case studies in this subcatchment: Barking Creek near A13, Barking Creekmouth, Chambers Wharf, Cuckolds Haven Nature Area, Greenwich Peninsula, Lower River Roding Regeneration Project, Mill Pool, Wandsworth Riverside Quarter Site Edit site Name Chiswick Eyot WFD water body codes GB530603911402 WFD (national) typology Intertidal WFD water body name Thames Middle Pre-project morphology Long, narrow island Reference morphology Desired post project morphology Maintained Heavily modified water body Yes National/international site designation UK - Local Nature Reserve Local/regional site designations Old Chiswick Conservation Area, Metropolitan Green Belt, Site of Metropolitan Importance for Nature, London Basin Natural Area, Strategic Nature Conservation Site Protected species present Yes Invasive species present Yes Species of interest Himalayan balsam (Impatiens glandulifera ), Smelt, Chinese mitten crab, European eel (Anguilla anguilla), Veronica anagallis aquatica, Garden angelica, Marsh Ragwort, Phragmites australis, buttercup (Ranunculus sp.) Dominant hydrology Dominant substrate River mud River corridor land use Urban 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) 290290 m <br />0.29 km <br />29,000 cm <br /> Project started 2014/12/23 Works started Works completed Project completed Total cost category 50 - 100 k€ Total cost (k€) Benefit to cost ratio High"High" is not a number. Funding sources Commercial partners, Local charities Cost for project phases Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname Investigation and design 1 - 10 k€ Natural History Museum Paul Clark Stakeholder engagement and communication Less than 1 k€ Royal Holloway University of London Martin Richardson Works and works supervision 100 - 500 k€ Thames21 Viv Richardson Post-project management and maintenance 1 - 10 k€ Natural History Museum Paul Clark Monitoring 1 - 10 k€ Natural History Museum Martin Richardson Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Invasive species Hydromorphology Structure & condition of intertidal zone Biology Historical willow holt Physico-chemical Restrict sediment mobilization Other reasons for the project Maintenance of local nature reserve Measures Edit Measures Structural measures Bank/bed modifications Bank stabilisation, Restoration of natural vegetation, Removal of invasive plants, Removal of invasive species, Bank improvement Floodplain / River corridor Planform / Channel pattern Other Non-structural measures Management interventions Reducing bank side collapse (source of sediment) Social measures (incl. engagement) Awareness raising, Community involvement, Citizen participation in the restoration project, the site is used by several schools and Thames Explorer Trust 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