The Hydro-Brake: A 21st century flood defence

The White Cart Water flood prevention scheme in Scotland incorporates the world's largest Hydro-Brake® structures, which are used to control the flow of water to prevent flooding upstream or downstream.

One of three Hydro-Brakes at Kirkland Bridge, part of the White Cart Water flood prevention scheme
One of three Hydro-Brakes at Kirkland Bridge, part of the White Cart Water flood prevention scheme

The White Cart Water Flood Prevention Scheme, a £53m flood storage solution commissioned by Glasgow City Council, was completed in 2011 and has brought much needed protection to nearly 2,000 properties in the south of the city.

The scheme saw the installation of the world's largest ever Hydro-Brake® structures, positioned at three dam sites outside of Glasgow. The Hydro-Brakes® control the flow levels of the White Cart Water riverway and its tributaries to prevent flooding in downstream urban areas.

What is a Hydro-Brake®?

Two Hydro-Brakes within open dam structure, Kirkland Bridge site
Two Hydro-Brakes within an open dam

The Hydro-Brake® design range is based on a vortex control system which regulates water flow via its self-activating features.

Manufactured by Somerset-based firm Hydro-International, they have typically been used in surface water drainage schemes, though more recently, much larger scale models, such as the one shown below, have formed the key feature of urban flood defence systems.

The cone-shaped, stainless steel structures, which at White Cart Water weigh around ten tonnes each and measure up to 8m x 6m, are positioned within an open concrete dam structure.

How does the Hydro-Brake® prevent flooding?

Upstream view of flood storage area (normal conditions) - Kirkland Bridge site
Upstream view of flood storage area (normal conditions) - Kirkland Bridge site

Under regular conditions, water passes through the Hydro-Brake® unrestricted and continues downstream at normal levels. At times of high flow e.g. during a rainstorm, the structure's internal geometry harnesses the natural energy of the river flow by creating a vortex effect. This holds back the water, releasing it at a controlled rate to prevent it spilling over riverbanks or defence walls downstream.

Agricultural land upstream then becomes a temporary storage area capable of holding millions of gallons of water. The Hydro-Brake® regulates the downstream flow at a measured rate until the stored water clears and levels return to normal.

What are the benefits?

As well as preventing flooding, the use of the Hydro-Brake® at flood defence sites brings some additional benefits. The steel structure has no pumps or moving parts, minimising the need for ongoing maintenance and the likelihood of mechanical failure, and no need for any form of power supply reduces its carbon footprint.

The measured regulation of flow during periods of high water levels also lessens the need for downstream defences such as flood walls. This improves the cosmetic nature of urban sections of such schemes, meaning residents can still see and appreciate the urban river environment.

The Hydro-Brake® structure allows the passage of fish and, at times of normal water levels, the movement of aquatic mammals through the surrounding concrete housing. The use of land upstream as a flood storage site also creates a rich and diverse wetland habitat.

White Cart Water Flood Defence Scheme

White Cart Water is a shallow, fast flowing river prone to rapid rises in water levels, causing flash floods in the south of Glasgow. Residents and businesses in the area have suffered over twenty significant flood events in the last century caused by the riverway bursting its banks, including several in the 1980s and 1990s when the districts of Paisley, Cathcart and Langside suffered severe damage from floodwaters.

In 2006, approval was granted for Glasgow City Council to proceed with plans to construct the Halcrow-designed defence scheme. Contractors Carillion were commissioned to construct dams, creating the flood storage areas, at three sites to the south of the city.

At Kirkland Bridge, three Hydro-Brakes® were installed, each of them a thick, stainless steel structure measuring 8m x 6m. The structures at both Blackhouse and Kittoch Bridge are made of a thinner stainless steel outer, encased in 600mm of concrete.

Downstream flood defence walls, White Cart Water Flood Defence Scheme (Spean St, Glasgow)
Downstream flood defence walls, White Cart Water Flood Defence Scheme (Spean St, Glasgow)

Further downstream within the city limits, VolkerStevin carried out the construction of flood walls, the raising of bridges and the installation of six pumping stations, works which presented various environmental challenges due to the dense urban development in the area. The utilisation of the flood storage areas upstream, and the regulation of water flow by the Hydro-Brake structures, meant the urban flood defence walls could be constructed up to one metre lower, minimising the visual impact for residents.

Construction was completed within five years, and within weeks of its official opening, the scheme was put to the test. Heavy rain and wind in November 2011 brought flooding to many areas of Scotland, however the south of Glasgow remained protected. Glasgow City Council estimated that £11m worth of flood damage was avoided in this period alone.

In June 2012, members of ICE's Water Expert Panel visited the Kirkland Bridge dam system and flood storage site. Our thanks go to Glasgow City Council and Halcrow for facilitating the visit.

More information on the scheme can be found at www.whitecartwaterproject.org. For more information on ICE's work in the water sector, or if you have any projects or initiatives you'd like to tell us about, please contact ben.mcalinden@ice.org.uk.

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