AquaRockBags for scour problems

Water infrastructure and civil engineering specialist Coffey was awarded a contract by Severn Trent Water to repair a section of the Derwent Reservoir.

The Derwent Reservoir is the middle of three reservoirs in the Upper Derwent Valley in the north-east of Derbyshire. The Ashop inlet allows water to flow from the River Ashop into the reservoir. The current structure in place created scour that occurred beyond the structure’s inlet apron.

Filling and preventing further scour holes

A scour hole around 4–5 m deep with an approximate volume of 210 m³ started to undermine the existing concrete structure of the spillway.

The objective of the project was to fill the scour hole and to provide an extension to the existing spillway that prevents further scouring immediately downstream of the Ashop inlet. Over 450 t of aggregate were required through a combination of AquaRockBags and a new gabion basket wall.

The large scour void occurred as a result from rip rap failure at the inlet channel to Derwent Reservoir.

AquaRockBags are the ideal scour prevention

AquaRockBags were considered an ideal solution to fill the scour void as the units are malleable, requirements for ground preparation were reduced and the AquaRockBags could simply be placed to infill the void. This saved time on site and reduced costs, as plant access was limited.

Given the considerable flows, AquaRock Bags were the preferred solution as they come delivered in two tonne units, reducing the potential for future geotechnical failures.

This was completed with a new section of reno mattress and concrete wall connecting to the existing structure.

“Because of the lack of storage space and difficult site access, the AquaRockBags were delivered pre-filled and lifted into place by crane. Installation with lifting rings incorporated into each of the pre-filled bags ensured simple and effective filling of the scour hole.”

Hayley Jackson, site agent for Coffey