Using willow and stone to secure a major gas pipeline and restore a collapsed riverbank

Gas Networks Ireland needed a natural solution to a ‘hard’ problem. Riverbanks had collapsed around the main Dublin to Cork gas line on both the Bride and Blackwater rivers, threatening the integrity of the 30-year-old hard engineering structures protecting the pipe and compromising the health of the river. Rivus designed and installed a nature-based solution that ticked multiple boxes.

The Problem

The main gas line that runs from Dublin to Cork crosses the River Bride (near Bridebridge) and the River Blackwater (near Careysville). Constructed in the 1980s, the pipe was secured in the riverbank using hard engineering structures made from sheet piles and large rock armour.

When hard engineering like this is used in a river floodplain where large floods are a natural occurrence, energy transfer from the man-made structures increases the rate of tractive force on the river bed below and on either side of them. Over time, this results in significant erosion in and around the structures, the eventual collapse of the structures, the collapse of the river bank, and the loss of soil from adjoining land.

The River Blackwater was suffering from severe bank erosion

The River Blackwater was suffering from severe bank erosion (top left). Rivus designed a resilient and multifunctional nature-based solution to restore the river (top right). The team used riprap stone and geocoir sackcloth (bottom left) along with willow panels (bottom right) in a tiered design.

The Rivus Solution

RPS Group (representing GNI) were investigating ways to stabilise all the affected structures and river banks, and they invited Rivus personnel to assist with the design process. Initially, hard engineering solutions were presented to the planning authorities but due to restrictions associated with the Special Area of Conservation status of the two rivers, the works had to be of ‘soft’ engineering design and construction.

Rivus is one of the few companies in Ireland with experience in both the design and construction of ecological engineering solutions, and we worked with RPS to submit a successful design to the Cork County planning authority. It incorporate both ecological ‘soft’ engineering solutions to protect the eroded river banks and more traditional hard engineering elements to stabilise and anchor the existing sheet piles. When the permission was granted, we were asked to tender for the works by Balfour Beatty, project managers for Gas Networks Ireland, and subsequently awarded the contract. We started work on the Blackwater and Bride rivers between July and September, 2017.

“Rivus designed and installed an innovative nature-based solution that secured the Dublin-Cork gas pipeline, restored the river and enhanced biodiversity. This is exactly the kind of multifunctional intervention we need for legacy problems in sensitive habitats."

- Balfour Beatty

The Result

We re-built and re-stabilised the riverbanks using panels made of living willow (spiling) and stone (rip rap) to protect them against the scouring effects of the flowing water. On the River Bride site, sand martins had begun to nest in the eroded riverbank faces, so we incorporated kingfisher and sand martin nesting boxes to accommodate them.

FOR MORE INFORMATION ON THIS PROJECT, CONTACT ALAN SULLIVAN

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