Case study:Saving Chiswick Eyot

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

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Project overview

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Status	In progress
Project web site	http://www.savingchiswickeyot.com
Themes	Economic aspects, Environmental flows and water resources, Habitat and biodiversity, Hydromorphology, Land use management - forestry, Monitoring, Social benefits, Urban
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.nhm.ac.uk
Partner organisations	Royal Holloway University of London, MoLA, University of Leicester, Thames21, Carillion, Port of London Authority, DHI
This is a parent project encompassing the following projects

Eyot erosion

Project summary

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Project team

Dr. Dave Morritt, Royal Holloway University of London. Dr. Paul Clark, Natural History Museum, London. Martin Richardson, PhD student RHUL & NHM.

Project

Chiswick Eyot (meaning island) is a small, historically important island in the Thames near Chiswick Mall that is subject to erosion caused in part by burrowing mitten crabs. Crab burrows occur in high densities at the site in excess of 30 per square metre. Individual burrows may be complex structures 70 cm in length and 5 cm in diameter so the amount of soil excavated is significant and the banks of the island are considerably weakened as a result thereby accelerating erosion. We have established an ‘ecosystem’ of partners to address the problem of maintaining the island employing best practice techniques. An initial 3D scan of the entire island was conducted in 2016 in association with the University of Leicester, the Museum of London Archaeology (MoLA), and Leica Geosystems. Subsequent, annual scans will permit calculation of the rate of erosion with analysis of the contribution made by mitten crab burrowing. A conventional topographic survey of part of one bank was undertaken by MoLA in 2000 and this will allow decadal scale assessment of the erosion rate caused by mitten crab burrows. 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 migration of the Eyot back and forth across the river, and permit analysis of changes to the island itself in terms of long term erosion. Additional remote sensing and environmental data sets are available and will be used to conduct a 3 dimensional analysis of the area around the Eyot within the context of the Thames catchment as a whole. Ecological changes will be inferred from analysis of the models and verified through species recording data from the NBN. We have engaged the local community and formed partnerships with other organisations including Thames 21, the River Restoration Centre, Leica Geosystems, DHI, MoLA, and Royal Holloway University of London. Additionally we plan to include international partners: the California department of fish and wildlife as well as several international researchers involved in invasive mitten crab work in Poland, Germany, China and elsewhere.

Monitoring surveys and results

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The first surveys have been completed. The island has decreased in size by over 40% since the 1930's and there is evidence of correlation with populations of Chinese Mitten crabs burrowing into the banks. The population dynamics of the crabs are characterized by large fluctuations related to environmental factors including temperature and rainfall. Larval development in the Thames requires a residency time of over a month which only occurs when flow rates are low. The burrows are long and wide which means that considerable quantities of sediment are mobilized during excavation but also the damage caused by burrowing is long-lived as the burrows continue to accelerate slumping for several years after the crabs have gone.

A second series of surveys will be conducted over the winter of 2017 and these will be used to assess the current rate of erosion and changes in the morphology of the island.

Lessons learnt

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Restoration work using traditional withes (willow saplings) has resulted in accretion to some areas of the bank with development of stabilizing vegetation. However, changes to the flow of the river caused by barriers made of withes have evidently caused some scouring in others, possibly because the barrier is too far from the bottom of bank at these points.

Image gallery

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Tree and slumping bank

Detail of entrance to mitten crab burrows in the banks of Chiswick Eyot.

Using the Leica P40 scanner

Accretion behind defence structures on the north bank of the Eyot

mitten crab burrows

Comparison 2002 to 2010 bottom of bank

Detail from a laser scan

LiDAR data

Photogrammetry of part of the bank

Photogrammetry point cloud of restored bank

Photogrammetry model made this year of the Easr bank

More detail of the East bank. Photogrammetry 2017

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 WFD water body codes GB530603911402 WFD (national) typology Intertidal WFD water body name Thames Middle 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 Yes Species of interest Chinese mitten crab (Eriocheir sinensis) Dominant hydrology Dominant substrate 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 2015/06/01 Works completed Project completed Total cost category 50 - 100 k€ Total cost (k€) Benefit to cost ratio 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€ Natural History Museum Diana Catovan Post-project management and maintenance 1 - 10 k€ Natural History Museum Paul Clark Monitoring 1 - 10 k€ Natural History Museum Diana Catovon Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Invasive species Hydromorphology Structure & condition of intertidal zone Biology Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Bank stabilisation, Restoration of natural vegetation, Removal of invasive plants, Removal of invasive species Floodplain / River corridor Planform / Channel pattern Bank restoration Other Non-structural measures Management interventions reducing bank side collapse (another main source of sediment) Social measures (incl. engagement) Awareness raising, Community involvement, volunteer engagement, Citizen participation in the restoration project 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