A new £3.1 million flood alleviation scheme in the North Yorkshire town of Northallerton is using innovative vortex flow control technology to reduce the risk of flooding to homes and businesses in the town.

Large Hydro-Brake® Flood Alleviation vortex flow controls have been installed upstream of the town’s refurbished culverts to protect flood-prone watercourses.  The Environment Agency project aims to provide sustainable, low-maintenance flood storage defences based on sound SuDS principles.

Northallerton and its surrounding villages have been plagued with flooding since the early 20th Century, with major floods most recently in 2000, 2008 and 2012 that caused widespread disruption and damage including to the town’s Friarage Hospital.

To reduce the risk of flooding to about 170 properties, the flood alleviation vortex flow controls have been installed in newly-refurbished culverts on the outskirts of the town.  They enable excess water to be held back in specially built flood storage basins in agricultural land on the approach to the culverts.

The Northallerton catchment, with the villages of Brompton and Romanby, is in a low lying river valley, surrounded by steep, well-drained agricultural land which makes it susceptible to flash flooding.  Largely culverted, the Turker and Sun Beck watercourses run through centre of the town, causing flood threats to amenities including Grade II listed buildings, conservation areas and listed monuments as well as the Hospital.  At times of peak flow, excess floodwaters can overtop the watercourse in the agricultural land on its approach to the culverts, sending flows to cause flooding in the East of the town.

Vortex technology – less flood storage needed and a low maintenance solution

Environment Agency area project manager Ian Cooke commented:

“The Sun and Turker Becks have repeatedly overtopped and threatened the town. That’s why, after consultation and looking at similar successful schemes in other areas, we decided to use upstream storage to reduce the flooding risk.”

“The resulting scheme at the urban boundary needs very low maintenance, and is resistant to blockage.  Our chosen solution meant that we used vortex control technology.  In addition, the ability to carefully-size the Hydro-Brake® Flood Alleviation vortex flow controls means we could minimise the back-up storage volumes even under high rainfall conditions.  As a result, the risk of the farm land on the outskirts of Northallerton flooding and threatening nearby developments and the town centre will be minimal in future.”

“The scheme is designed to also improve protection to the area from flash floods. The design meets sustainable principles, by attenuating (holding back) excess flows and allowing them to discharge at a controlled rate.”

The giant cone-shaped Hydro-Brake® Flood Alleviation vortex flow control devices installed in the culverts are based on an industry-standard method of flow attenuation, most frequently used in much smaller dimensions as part of urban surface water drainage designs.  Hydro’s UK Stormwater Operations Manager Andy Kane explained:

“We have individually-sized both the controls at Northallerton to create an optimal internal geometry that delivers best-possible hydraulic performance with the minimum amount of upstream storage. “

“Compared to alternative flood control devices such as orifice plates or penstocks, the vortex flow controls have a larger opening, so more water is able to flow through the culvert unimpeded, meaning less flood storage is needed.  At the same time, there is less risk of blockages.  This, together with fact that the flow controls have no moving parts or power-requirements, means they require minimal maintenance.”

The installation at Northallerton follows successful flood alleviation schemes built on the White Cart Water in Glasgow, the River Douglas in Wigan and at Weedon Bec in Northamptonshire since 2002.