Case study:Aubourn Rock Ramp and Habitat Works

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Location: 53° 9' 7.49" N, 0° 38' 10.62" W

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Project overview

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Status	Complete
Project web site
Themes	Fisheries, Habitat and biodiversity
Country	England
Main contact forename	Matt
Main contact surname	Parr
Main contact user ID
Contact organisation	Environment Agency
Contact organisation web site	http://www.gov.uk/government/organisations/environment-agency
Partner organisations
Parent multi-site project	Case_study:Upper Witham Restoration
This is a parent project encompassing the following projects	No

Constructed Rock Ramp.

Project summary

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Aubourn Weir, located in the lower reaches of the Upper River Witham, presented a major barrier to upstream fish and eel passage and the heavily-modified channel in the vicinity, lacked morphological and habitat diversity resulting in poor fish populations. Also affected by high levels of phosphates, the overall Ecological Status of this section of the river is classified as Moderate.

The key objectives of the Aubourn project were to enable fish and eel passage at the weir and to undertake additional enhancements to improve the channel diversity. The wider project, from Bassingham Bridge to beyond Aubourn Weir, sought to enhance the heavily-modified channel using existing riverside trees to create in-stream deadwood habitat, improve flow variation and provide valuable refuges for fish and invertebrates.

There were two parts to the project: construction of the rock ramp fish pass and associated bed enhancements in the vicinity of Aubourn Weir, and extensive woody habitat creation from Bassingham downstream to beyond Aubourn Weir.

• Rock Ramp - Using large rocks and steel sheet piling to maintain the water levels, a series of stepped pools, rising c1m in c20cm increments, were constructed to create the “rock ramp” which now enables fish and eels to negotiate the former obstruction.
• Pools – Five pools were excavated in the river bed, three above the new rock ramp and two below it. The excavated material was deposited against the bank immediately upstream of each pool to narrow the channel and speed up the flow - a technique known as “dig-and-dump”.
• Woody habitat - Riverside trees, in particular those that had collapsed in to the river or were in imminent danger of doing so, were selectively hinged and/or secured into the channel and along the bank throughout the whole of the 3.25km reach. The large woody material creates flow variation and provides refuges for fish and invertebrates as the river level and speed of flow changes.

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Image gallery

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Weir Pre-works

Tree 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 Anglian River basin Witham Subcatchment River name Upper Witham Area category 10 - 100 km² Area (km2) Maximum altitude category Less than 100 m Maximum altitude (m) 4646 m <br />0.046 km <br />4,600 cm <br /> Dominant geology Calcareous Ecoregion Great Britain Dominant land cover Arable and Horticulture Waterbody ID GB105030056760 Other case studies in this subcatchment: Belton Floodplain Reconnection and River Restoration, Dysart Park, Grantham Habitat Improvement, Grantham Blue Green - Urban Reach, Little Ponton, Manthorpe Floodplain Reconnection, Papermill Weir Section in-channel restoration, River Witham Great Ponton, Stainby Road, Colsterworth, Syston and Barkston Restoration, Upper Cringle Floodplain Restoration Project... further results Site Edit site Name Aubourn Rock Ramp and Habitat Works WFD water body codes GB105030056780 WFD (national) typology WFD water body name Witham Confluence Cringle Brook to Confluence Brant Pre-project morphology Impounded Reference morphology Desired post project morphology Heavily modified water body Yes 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) 32003,200 m <br />3.2 km <br />320,000 cm <br /> Project started 01/05/2016 Works started Works completed Project completed Total cost category 100 - 500 k€ Total cost (k€) 126000126,000 k€ <br />126,000,000 € <br /> 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 Land drainage Hydromorphology Biology Fish Physico-chemical Phosphate Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Tree hinging over long section and large rock ramp installation to replace existing large weir that was a barrier to fish passage. 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 Project Case Study Additional links and references Edit links and references Link Description Supplementary Information Edit Supplementary Information