Case study:River Idle Hallcroft (Tiln) Weir Fish Pass

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Location: 53° 20' 35", -0° 57' 39"
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Project overview

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Status Complete
Project web site
Themes Fisheries
Country England
Main contact forename Joel
Main contact surname Rawlinson
Main contact user ID
Contact organisation Environment Agency
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Parent multi-site project
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Project summary

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To meet targets set by the Water Framework Directive (WFD), the Environment Agency completed a programme of habitat improvement works on the River Idle which is a major tributary to the River Trent. This project concerns Hallcroft Weir (AKA as Tiln Weir) in Retford, Nottinghamshire (SK69275 83396).

Hallcroft Weir, located on the River Idle in Nottinghamshire is approximately 30-35km from the confluence at which the Idle meets the tidal Trent. Not including the sluice / pumping station control structures at the confluence, Hallcroft weir is the first physical barrier encountered by upstream migrating fish. Although originally passable to some species of fish, a combination of head loss and flow limited certain species ability to pass the weir.

Hallcroft Weir is an Environment Agency owned asset. The weir is a broad crested type weir spanning the full channel width and running perpendicular to the flow. Downstream of the weir is a non-official rock ramp extending from approximately 1m downstream of the weir toe for 15m.

The weir at Hallcroft prevented free movement of fish, particularly in an upstream direction. It was impassable to many species of fish under most flow conditions due to velocity and depth of flow.

The project aim was to increase the migratory ability of all fish species in the River Idle and in particular eels. This will lead to a more sustainable population within the catchment as the work will allow the migrating eels and other fish species to reach more upstream habitat.

The total project costs a 260,000GBP.

Monitoring surveys and results

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Following implementation of the fish pass improvements, we will monitor the impact through on-going survey work, which can be compared to past survey results. We have long term monitoring sites up and downstream of Hallcroft weir that have been monitored since the 1990’s - upstream at Eaton and downstream at Chain Bridge. Samples are usually taken in early May, so there will be a sample just before the project takes place and then we will get post project result the following May. These standardised monitoring results can also be compared to catch returns from the local angling clubs.

Lessons learnt

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Image gallery

Before works
The weir crest following debris removal
Larger boulders forming the channel bank toe
Hallcroft May (1).jpg
Hallcroft May (2).jpg
Hallcroft May (3).jpg
Hallcroft May (4).jpg
Hallcroft 17 Jun 2015.jpg
Hallcroft completed 1 July 2015.jpg
Hallcroft completed 1 July 2015 2.jpg

Catchment and subcatchment


River basin district Humber
River basin Idle and Torne


River name River Idle from Maun/Poulter Conf to Tiln
Area category 100 - 1000 km²
Area (km2)
Maximum altitude category 100 - 200 m
Maximum altitude (m) 105
105 m
0.105 km
10,500 cm
Dominant geology Calcareous
Ecoregion Great Britain
Dominant land cover Arable and Horticulture
Waterbody ID GB104028058091


WFD water body codes GB104028058091
WFD (national) typology
WFD water body name River Idle from Maun/Poulter Conf to Tiln
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)
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Average channel gradient
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Project background

Reach length directly affected (m)
Project started 2011/08/31
Works started 2015/04/06
Works completed 2015/06/23
Project completed 2015/07/01
Total cost category 100 - 500 k€
Total cost (k€) 366
366 k€
366,000 €
Benefit to cost ratio
Funding sources Environment Agency Flood and Coastal Risk Management

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

Reasons for river restoration

Mitigation of a pressure Barriers to fish migration
Other reasons for the project


Structural measures
Bank/bed modifications Rock ramp construction
Floodplain / River corridor
Planform / Channel pattern
Non-structural measures
Management interventions
Social measures (incl. engagement)


Hydromorphological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Biological quality elements

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Physico-chemical quality elements

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Any other monitoring, e.g. social, economic

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Monitoring documents

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Supplementary Information

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