Ballygawley Water Flood Alleviation SchemeWhole Project Award |
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Project Team
Client: DARD Rivers Agency
Designer: DARD Rivers Agency
Contractor: BSG Civil Engineering LTD
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Project summary
The Ballygawley Water flows through Ballygawley village and adjacent to St Ciaran’s High School in County Tyrone, Northern Ireland. Historically there have been several flooding events during times of heavy rainfall which have severely affected properties adjacent to the watercourse. The most recent flood events occurred during heavy and prolonged rainfall on 16 August 2008, 17 October 2011 and 24 October 2011.
Flooding problem at St Ciarans High School
The works reduced the risk of flooding at three locations along the watercourse and providing flood defence to a large Secondary School (c. 800 pupils), a Nursery School, a Church Hall, a Commercial Auto Garage and seven Residential Properties.
The main work items included:
• Construction of approximately 650 linear metres of sheet piled flood wall with reinforced concrete capping beam and concrete stem wall;
• Construction of approximately 240 linear metres of king post (soldier pile) reinforced concrete floodwall;
• Construction of approximately 205 linear metres of reinforced concrete flood wall;
• Construction of approximately 65 linear metres of sheet piled flood wall with landscaped earth bank;
• Construction of approximately 60 linear metres of concrete flood wall with landscaped earth bank;
• Installation of back drainage to all flood defence works;
• Installation of fishery environmental enhancement habitat units.
Completed project in Ballygawley Village
Challenges faced and Achievements
Ecology and Biodiversity
For the Ballygawley scheme it was a significant goal of the team to restore and improve fishery habitat for the UK BAP significant species of Brown Trout and Salmon. Consultations with DCAL Inland Fisheries, Rivers Agency Environmental Section and NIEA were undertaken and recommendations made by these bodies incorporated into the overall scheme.
From this consultation it was highlighted that the river channel reach of 600m around St Ciarans High School would be enhanced via the construction of fishery habitat units. These included:
| Spawning Gravel Beds | – a specific sized and DCAL Fishery approved gravel to improve the spawning environment. |
| Nursery Beds | – to enhance the fishery environment for younger fish, additional gravel and rock olives were placed to allow for areas of rest and flow variations. |
| Pools & ‘D’ Shaped Groynes | – these were installed separating the nursery and spawning beds and introduced flow and environment variations hence improving the environment for older fish. |
Completed Fishery Enhancement Measures
To ascertain the success of the fishery enhancement measures an electro-fishing survey and monitoring plan was established. A pre works figure was ascertained along with a control site setup. The results after 1 year show major improvements in salmonid biomass, predominantly from the density increase of older Brown Trout. Further study is planned over a 5 year period.
Electro Fishing Survey and Result
Otter footprints were also identified during the project in an area of poor vegetation cover. This provided scope to include an artificial otter holt within the project and was delivered reusing surplus material from the main works, i.e. off cuts of reinforcement mesh and drainage pipe.
Otter Holt Construction
People and Communities
The nature of the flood alleviation scheme helps to deliver a more sustainable way of living for the local community it serves. The project team also aimed to engage, enhance relationships and implement local improvements at every step of the project.
Through economic appraisal all tangible and intangible benefits of the project were identified, these included the direct financial cost and the stresses and disruption that a flood event exerts on the local population. At design stage local amenity was considered to include the creation of extra pathway within a local park and a concrete formwork finish was specified to reduce the visual impact of the flood wall.
Completed flood wall at St Ciarans High School
At construction stage the project team saw engagement with St Ciarans High School as an essential activity regarding community liaison. Project team members delivered three separate talks and presentations to classes including Geography and Careers; the contents of these presentations included explaining the need for flood alleviation, construction techniques and promotion of a career in civil engineering. BSG Civil Engineering also took on board the contract stipulations to supply work experience through the DEL Steps to Work Programme. They held 2 phases of interviews leading to a successful candidate from the local area being employed on a 13 week training experience programme. He successfully completed the training programme and BSG took him on as a full time site agent; he is currently working on the Rivers Agency Beragh Flood Alleviation Scheme with BSG. The contractor also non-destructively deconstructed existing structures to allow reuse by the local riparians; this included 50m of 600mmØ concrete pipes and 600m of palisade fencing. |
Presentation delivered to St Ciarans High School |
Water Environment
As this project obviously is in close proximity to the Ballygawley Water it was essential that the works were undertaken in a water environmentally sensitive manner. The contractor planned the works to ensure that minimal works from the watercourse channel were required and all environment protection methods suggested from the consultations with DCAL Inland Fisheries, Rivers Agency Environmental Section and NIEA were implemented; this included the maintenance of a green vegetative barrier between works and watercourse to intercept potential silt run-off and retaining mature trees by amending the line of the flood defence.
Photos of green vegetative barrier
Climate change scenarios were fully modelled during the design process and incorporated within the final scheme. Oversized back drainage and tideflex valves were installed behind all flood defences, these systems will retain run-off from the protected urban areas until the flood peak has subsided and then discharge to the watercourse.
To what extent did the use of CEEQUAL influence your project?
DARD Rivers Agency as a client aim to deliver all capital works in a sustainable manner and undertaking a CEEQUAL assessment allowed us to not only assess the sustainability performance of the project but also encouraged the entire project team to actively consider and act on sustainability issues.
At the design stage sustainability issues encompassing environmental, social and economic factors were comprehensively addressed through the Feasibility Study, Economic Appraisal and Detailed Design stages of the project.
At construction stage methods to achieve increased environmental and social performance were discussed at every site progress meeting and subsequently implemented. The construction workforce also developed a keen interest in environmental protection and invasive species.
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| Whole Project Team, L->R, Paul McSparran - BSG Contracts Manager, Oliver McGurn - BSG Site Manager, Stephen Dawson - Rivers Agency Project Sponsor, Thomas Cooney - Rivers Agency Site Supervisor, James Kelly - Rivers Agency Project Manager, Alan McWatters - Rivers Agency CEEQUAL Assessor. | Rivers Agency project team, L->R, Stephen Dawson - Rivers Agency Project Sponsor, Thomas Cooney - Rivers Agency Site Supervisor, Pat Aldridge - Rivers Agency Director of Engineering, James Kelly - Rivers Agency Project Manager, Alan Mcwatters - Rivers Agency CEEQUAL Assessor. |