Case study:Lodge Burn cascade fish pass and culvert bed restoration (as part of the Lodge Burn FAS)

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Location: 55° 7' 58", -6° 40' 0"
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Project overview

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Status Complete
Project web site
Themes Fisheries, Flood risk management
Country Northern Ireland
Main contact forename Gareth
Main contact surname Greer
Main contact user ID
Contact organisation Rivers Agency Northern Ireland (DARDNI)
Contact organisation web site
Partner organisations
Parent multi-site project

Lodge Burn Flood Alleviation Scheme

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encompassing the following
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Project summary

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The aim of the project is to install a new cascade fish pass to improve fish passage through a reach of the Lodge Burn in Coleraine as part of a wider Flood Alleviation Scheme. A perched culvert with a concrete apron outfall located in the center of the town was causing disruption to fish passage and sediment transport. The location of this structure meant that re-design of the reach had to work within a very confined space between two high flood walls, which encompassed installation of the cascade sequence and re-design of the culvert bed.

The works were carried out in four key stages; 1. Flow management; works to install the step pool sequence and improve the culvert bed had to be conducted in the dry. A fully isolated dry working area was achieved by sandbagging and over-pumping. 2. Modify culvert bed; it was necessary to ensure passability for fish through the culvert, therefore the new culvert bed was fixed 300mm below the previous bed 3. Install natural bed in culvert; from a mix of cobble and boulders 4. Remove concrete apron and install cascades Spacing between cascades was 6m, therefore in total the pass extended for 36m downstream of the culvert.

It was envisaged that some maintenance of the pass would be needed, so a demountable barrier was included in the floodwall design to facilitate channel access if required.

The project is an excellent example of what can be achieved to improve fish passage in a confined space. Cascade strength was a major consideration as failure of the top cascade would have left a perched culvert once again, therefore it was deemed better to over-engineer the first two cascades to ensure their long term stability. In terms of aesthetics the new pass has had a positive response, however flooding shortly after construction caused some damage to the face of the first cascade as well as gravel and cobble washout from culvert. This resulted in infilling of the pools, which was removed after flooding, and highlighted the importance of pool design incorporating sufficient self-maintaining processes i.e. sufficient flow through to maintain the pool depth. The remaining cobble within the culvert is now deemed to be stable.

Community Involvement - "Salmon in the classroom" scheme undertaken at a local primary school, fish release highlighted on BBC TV and local press.

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Lessons learnt

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Image gallery

Culvert outlet pre-works was causing a major obstruction to fish passage (Rivers Agency)
Culvert apron pre-works (Rivers Agency)
construction of new cascade pool sequence (Rivers Agency)
step pool post works (Rivers Agency)
new cascade 4 months post-construction(Rivers Agency)
New culvert bed in construction (Rivers Agency)

Catchment and subcatchment


River basin district Northern Ireland
River basin Bann


River name Lodge Burn
Area category 10 - 100 km²
Area (km2) 16.41
16.41 km²
1,641 ha
Maximum altitude category
Maximum altitude (m)
Dominant geology
Ecoregion Ireland and Northern Ireland
Dominant land cover Agriculture
Waterbody ID

Other case studies in this subcatchment: Lodge Burn Flood Alleviation Scheme


Name Lodge Burn cascade fish pass and culvert bed restoration
WFD water body codes GBNI1NB030301223
WFD (national) typology
WFD water body name
Pre-project morphology Closed culvert, Artificial bed, Straightened
Reference morphology Bedrock cascade, Step-pool
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 Salmon
Dominant hydrology
Dominant substrate Cobble, Gravel
River corridor land use Improved/semi-improved grassland/pasture, Urban, Grassland
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

Reach length directly affected (m) 40
40 m
0.04 km
4,000 cm
Project started 2012/05/01
Works started
Works completed
Project completed 2012/05/31
Total cost category
Total cost (k€) 102
102 k€
102,000 €
Benefit to cost ratio
Funding sources part of Coleraine flood alleviation scheme

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, Flood risk management
Other reasons for the project


Structural measures
Bank/bed modifications Creation of fish passes, Bed reprofiling
Floodplain / River corridor
Planform / Channel pattern Creation of pool cascade
Non-structural measures
Management interventions
Social measures (incl. engagement) Engagement with schools, Media


Hydromorphological quality elements

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Before measures After measures Qualitative Quantitative

Biological quality elements

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Physico-chemical quality elements

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Monitoring documents

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Supplementary Information

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