Articles & Case Studies

Morpeth bypasses flood risk with Graf UK's EcoBloc Flex

Posted: Wednesday 13th April 2016

In a bid to eliminate flood risk and to provide an effective, controlled rainwater drainage solution, water management specialist Graf UK has installed a 620m3 EcoBloc Flex stormwater tank at a new 13-mile bypass in Morpeth, Northumberland.

The project's contractors were keen to find a robust stormwater tank with high volume capacity, whilst at the same time minimising costly excavation work. They also wanted a system that would be easy to inspect and straightforward to maintain, ensuring optimum long-term performance.

Kevin Reed, national specification manager at Graf UK, explains: "Before we designed the EcoBloc Flex system, the original proposition involved large, four-metre diameter GRP tanks to be placed up to nine metres underground - with four tanks on either side of the road. The size of these tanks, their connecting pipework and the depth of the install would have called for extensive excavation, and the stormwater from the road would have needed to drop a significant distance into the collection manhole at full speed - creating a strain on the system.

"After analysing the original plans and realising they weren't suitable, the contractors came to us for an alternative solution for the bypass - and that's when they specified the EcoBloc Flex system. In doing so, they were able to have one tank instead of eight. What's more, this could be placed much higher up in the ground, raising it by nearly six metres - and making for significant excavation savings in the process. Its elevated position also means that when rainwater now enters the collection manhole at full force, it has a much shorter drop into the system."

Pipework in the bypass's gullies collects the rainwater from the road and feeds it into the single EcoBloc Flex attenuation tank. This then uses a vortex flow controller to discharge the water into the culvert at a controlled, slow speed - meeting Northumberland County Council's requirement of 10 l/s. Graf UK installer Gareth Robinson says: "The contractors gave us a 3D Revit design of the system, which meant we could clearly see how the tank would sit on the hillside. Not only did it provide a representative 3D view of the tank and ground cover, it also helpfully showed us where its inlets and outlets needed to go, as well as invert levels.

"EcoBloc systems are fantastic to install. I've constructed all types of stormwater management solutions over my career and this is by far the easiest. The engineering is great and whether it's the pipework or the chambers - it all just clicks into place! The challenge we faced with this particular install was due to it being built into the embankment of the road on a gravel plateau, rather than underground. This is quite unusual for stormwater installs, so we needed to take the necessary safety precautions that come with working at height - for example, surrounding the system with fall-arrest bean bags."

Providing a void ratio of 96 per cent, EcoBloc Flex holds three times the storage capacity of a typical gravel infiltration ditch, while its compact design requires minimum space and soil excavation. The tanks also have a heavy-duty lorry-bearing capacity of up to 60 tonnes (with an 800mm earth covering). With in-built inspection channels and a fully-integrated shaft, EcoBloc Flex can be easily monitored using standard drainage camera technology, which can be used to check the system for any silt build up. If required, this can then be removed using jetting and pumps.

For the two-year construction period of the bypass, the contractors also specified two Graf UK Klaro E wastewater treatment systems for its site offices. Despite mains drainage being available, they opted for a more environmentally friendly solution - one that didn't put any extra stress on the sewage system or local treatment plants. A 22-PE system (with two inter-linked 4,800 litre tanks) was specified for the site's north compound, and a 10-PE system (with one 4,800 litre tank) for the south compound.

Graf UK's Klaro E system provides an impressive cleaning performance of up to 98 percent. It mechanically holds back solids in one chamber and uses a separate sequencing batch reactor (SBR) chamber to treat the wastewater. This is an aeration process, where microorganisms biologically clean the water, allowing sludge to sink to the bottom and a clarified water zone to form at the top - ready to be discharged.

Kevin Reed concludes: "This project is an excellent example of the real flexibility EcoBloc Flex offers. These modular tanks can be made to suit any shape or size and can be positioned as shallow or as deep underground as required. Their large void ratio also means they can hold more water, without requiring as much valuable space. It was this versatility that made EcoBloc Flex the perfect stormwater solution for the Morpeth bypass project. We're also delighted that our Klaro E tanks played such an important role for the construction team, providing a reliable, environmentally friendly wastewater solution for the site offices."

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