Case study:Holnicote multi-objective flood risk management demonstration project

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Location: 51° 12' 23.64" N, 3° 33' 33.43" W

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Project overview

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Status	In progress
Project web site	http://www.nationaltrust.org.uk/holnicote-estate/
Themes	Economic aspects, Environmental flows and water resources, Flood risk management, Habitat and biodiversity, Hydromorphology, Land use management - agriculture, Land use management - forestry, Monitoring, Social benefits, Water quality
Country	England
Main contact forename	Nigel
Main contact surname	Hester
Main contact user ID
Contact organisation	National Trust
Contact organisation web site	http://www.nationaltrust.org.uk/
Partner organisations	Penny Anderson Associates Ltd, University of Exeter, Environment Agency, Defra, JBA Consulting, JBA Trust
Parent multi-site project
This is a parent project encompassing the following projects	No

© Gene Hammond, Penny Anderson Associates Ltd

Project summary

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The National Trust Holnicote Estate is situated adjacent to the uplands of Exmoor and comprises around 40km2 of land draining the catchments of the Aller and Horner Water from Exmoor northwards through woodland, grassland and arable areas towards Porlock Bay. The key flood risk receptors in the catchments are the villages of Allerford, West Lynch and Bossington. There is nearly 100 properties in these villages at risk of flooding from the watercourses, which are influenced by a legacy of flow constrictions within the drainage networks, such as narrow historic stone bridges, and the lack of undeveloped channel and floodplain capacity through the built-up areas.

Driven by Defra, supported by the Environment Agency and managed by the National Trust, this project hopes to demonstrate that by looking at whole catchments and strategically targeting shifts in rural land management practices, sustainable support to flood management may be achieved. In addition, it is recognised that through rural land management change and intervention comes the opportunity to enhance the provision of a range of other ecosystem services within catchments. These include landscape quality, biodiversity, carbon stewardship, water quality, amenity and recreation.

The principal objectives of the Holnicote project, which is currently scheduled to run until 2015, are:
- To establish a robust hydrological monitoring programme across the study area
- To identify potential catchment (hillslope and floodplain) interventions that may contribute to managing flood risk
- To demonstrate the practical implementation of catchment interventions (e.g. changes to land use, land management practices, and hydrological connectivity)
- To assemble evidence, both from recorded datasets and hydrological/hydraulic modelling, about the impact of the catchment interventions on runoff and flood dynamics
- To assess what the evidence reveals about the potential or actual benefits, in terms of flood risk management and the delivery of a range of other ecosystem services

Monitoring surveys and results

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The ecosystem services assessment being undertaken for the project aims to provide an evaluation of the various goods and services provided by the existing ecosystems across the Holnicote Estate, and those anticipated following the range of expected habitat modifications scheduled as part of the catchment interventions. In addition, based on the most robust information available, the assessment will provide an evaluation of the value of these anticipated goods and services relative to the capital investment.

The National Trust is also co-funding a PhD student at Exeter University to establish whether the catchment management interventions being implemented can help to improve water quality. The research will complement the catchment-wide hydrological monitoring taking place with some additional chemical, biological and physical water quality monitoring to examine the effectiveness of the intervention measures to also meet water quality objectives.

For more information, refer to http://ccmhub.net/wp-content/uploads/2013/01/Holnicote-Position-Paper-v9.pdf

Lessons learnt

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Image gallery

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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 South West River basin South and West Somerset Subcatchment River name Aller Area category 10 - 100 km² Area (km2) Maximum altitude category 200 - 500 m Maximum altitude (m) 426426 m <br />0.426 km <br />42,600 cm <br /> Dominant geology Calcareous Ecoregion Great Britain Dominant land cover Arable and Horticulture Waterbody ID GB108051020230 Site Edit site Name Holnicote estate WFD water body codes GB108051020230 WFD (national) typology Aller 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 Edit project background Reach length directly affected (m) Project started Works started Works completed Project completed Total cost category Total cost (k€) Benefit to cost ratio Funding sources Cost for project phases Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname Investigation and design 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 Biology Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Floodplain / River corridor Planform / Channel pattern Other Non-structural measures Management interventions Social measures (incl. engagement) 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 http://ccmhub.net/wp-content/uploads/2013/01/Holnicote-Position-Paper-v9.pdf An analysis of the impacts of rural land management change - A position paper http://www.youtube.com/watch?v=3MbkfVQs8Z8 Video: Going with the flow - how the National Trust manages water and flooding on the Holnicote estate http://ccmhub.net/case-studies/holnicote-case-studies/holnicote/ Catchment change management hub - Holnicote case study http://ccmhub.net/wp-content/uploads/2013/01/Holnicote-final.pdf Holnicote case study summary Supplementary Information Edit Supplementary Information