Case study:Knepp Rewilding Project

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Location: 50° 58' 40.98" N, 0° 21' 33.26" W

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Project overview

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Status	Complete
Project web site	http://knepp.co.uk
Themes	Environmental flows and water resources, Flood risk management, Habitat and biodiversity, Hydromorphology, Land use management - agriculture, Social benefits, Water quality
Country	England
Main contact forename	Penny
Main contact surname	Green
Main contact user ID	User:Penny Green
Contact organisation	Knepp Castle Estate
Contact organisation web site	http://knepp.co.uk
Partner organisations	Environment Agency, Sussex Wildlife Trust, Royal HaskoningDHV, West Sussex County Council and Natural England
Parent multi-site project
This is a parent project encompassing the following projects	No

View of the river from the tree platform

Project summary

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Jointly funded by Natural England and the Knepp Estate, the restoration of the upper reaches of the River Adur lies at the heart of the largest rewilding project in lowland UK.

The work, carried out by the Environment Agency, has involved removing 4 weirs, returning 2.4km of canalised river to its original meanders and linking it to 5.5kms of restored floodplain upstream.

It is part of a landscape-scale conservation enterprise aimed at restoring the full range of hydrological processes from the moment raindrops fall on the land, filtering through vegetation and the soil, to their passage into watercourses towards the sea.

This reach of the River Adur was enlarged and diverted to the edge of the floodplain at least two hundred years ago, in an attempt to improve land drainage and allow the land to be farmed more productively. This extensive modification created a deep, uniform trapezoidal channel that supported very little flow or habitat diversity and was largely cut off from its floodplain in all but the largest floods. The extent of channel enlargement meant that flows became very low during dry summer periods, with parts of the river resembling a series of connected ponds rather than a flowing channel. A sluice and two stepped weirs were installed in an attempt to maintain depths of flow, but these impounded flows, encouraged sedimentation and limited fish passage. As a result of these modifications, natural river processes were limited and the river did not support the range of habitats that would be expected, resulting in a failure to reach Good Ecological Status under the Water Framework Directive.

The main aim of the restoration project was therefore to physically modify the existing channel to restore natural river processes, reconnect the river to its floodplain, and create the conditions that are required to support a rich and varied range of habitats for plants, invertebrates and fish. The project formed part of the wider Knepp Castle Rewilding Project, which aims to produce a large scale minimal-intervention landscape.

Creation of 1 km of new meandering river channel with naturally variable bed and bank profiles. Re-naturalisation of an additional 1.5 km of channel through bank re-profiling. The uniform, high banks were “pushed” into the channel to create a low flow channel with natural bank profiles that support a range of emergent and marginal habitats.

The new channel has a much smaller capacity than the modified channel that it replaced, concentrating low flows and improving floodplain connectivity during periods of higher flow. Blocking and diversion of floodplain drains and creation of scrapes to retain water on the floodplain.

Works included: Realignment of 1km river channel to its former naturally meandering course. Removal of four obsolete in-channel structures to restore natural flow and sediment transport processes and allow the free passage of fish. Creation of two backwaters to provide valuable habitats for aquatic plants and invertebrates.

Monitoring surveys and results

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Image gallery

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Completed works

Pre-works – canelised river with former meanders visible in floodplain

Completed works with LWD

River restoration in progress

Completed works

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 East River basin Adur and Ouse Subcatchment River name Adur Area category 10 - 100 km² Area (km2) Maximum altitude category Less than 100 m Maximum altitude (m) 6969 m <br />0.069 km <br />6,900 cm <br /> Dominant geology Calcareous Ecoregion Great Britain Dominant land cover Improved grassland Waterbody ID GB107041012270 Site Edit site Name WFD water body codes GB107041012270 WFD (national) typology WFD water body name Knepp Rewilding Project 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) 10001,000 m <br />1 km <br />100,000 cm <br /> Project started 2006/01/01 Works started 2011/09/01 Works completed 2013/12/31 Project completed 2013/12/31 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 Barriers to fish migration, Land drainage, Impoundments (not hydropower) Hydromorphology Freshwater flow regime, Continuity of sediment transport, Quantity & dynamics of flow, Structure & condition of riparian/lake shore zones, Substrate conditions Biology Fish, Invertebrates Physico-chemical Other reasons for the project This reach of the River Adur was enlarged and diverted to the edge of the floodplain at least two hundred years ago, in an attempt to improve land drainage and allow the land to be farmed more productively. This extensive modification created a deep, uniform trapezoidal channel that supported very little flow or habitat diversity and was largely cut off from its floodplain in all but the largest floods. The extent of channel enlargement meant that flows became very low during dry summer periods, with parts of the river resembling a series of connected ponds rather than a flowing channel. A sluice and two stepped weirs were installed in an attempt to maintain depths of flow, but these impounded flows, encouraged sedimentation and limited fish passage. As a result of these modifications, natural river processes were limited and the river did not support the range of habitats that would be expected, resulting in a failure to reach Good Ecological Status under the Water Framework Directive. The main aim of the restoration project was therefore to physically modify the existing channel to restore natural river processes, reconnect the river to its floodplain, and create the conditions that are required to support a rich and varied range of habitats for plants, invertebrates and fish. The project formed part of the wider Knepp Castle Rewilding Project, which aims to produce a large scale minimal-intervention landscape. Measures Edit Measures Structural measures Bank/bed modifications Bank modification, Re-profiling, Creation of low flow channel, Habitat restoration, Creation of low flow channel, Barrier removal, Creation of backwaters, Introducing large woody debris, Riverbed restoration Floodplain / River corridor Floodplain reconnection, Scrapes, Increase water retention area, Wetland habitat Planform / Channel pattern Channel realignment, Re-meandering, Enhancing flow diversity, Habitat restoration, Meandering channel Other Selective removal of organic muds and sludge contaminated with toxic, Create more natural flow regime, Improvement of natural flows, Improving fish migration Non-structural measures Management interventions Flow management 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://https://www.youtube.com/watch?v=IHZr1FUCP8g&feature=player embedded&list=PL3eoaBdiC8XR5xuXn1VwVFxHwvn0HLCKo YouTube link Supplementary Information Edit Supplementary Information