Spillway solution specifies Grasscrete®
Lately Grasscrete has enjoyed a “green renaissance†recognised for its part in greener construction, eco environments and sustainability. With a leading reputation in drainage solutions Grasscrete® maintains its authority supplying the key component material in critical flood alleviation systems across the UK.
Grass Concrete Ltd has recently installed 9391m² of Grasscrete system as part of the Cobbins Brook Flood Alleviation Scheme close to Waltham Abbey in Essex. A self draining grass reinforcement system Grasscrete has become a byword for flood and drainage systems across the UK with more than 100 installations this year alone.
The Environment Agency has closely managed projects across the UK to guarantee that local flood defences have been screened for their environmental impact. At Cobbins Brook the large expanse of embankment spillway required an effective overspill drainage management system and Halcrow Group Ltd selected Grasscrete as a first choice environmental alternative.
Grasscrete is often used for slope protection works whatever the sector, be it highways, rail or rivers. The Cobbins Brook project has seen a combination of excavation and embankments around the spillway and pump station. Working closely with contractors Jackson Civil Engineering the Grasscrete was installed in stages as each embankment was ready. The system installed used 9391m² of GC2 with A252 reinforcing mesh in a 150mm slab; total installation time for Grasscrete was just 10 weeks.
At Cobbins Brook the spillway slope is designed to handle high impact water flow from the overtopping of the embankment up to max volume of 754,000m3. Grasscrete has approved test flow rates in excess of 8 metres/second, a critical benefit in the design of grassed waterways.
Water flow tests also establish that long stemmed grass is hydraulically efficient; under peak demand it simply flattens to aid the water flow. This is particular beneficial in the design of channels and spillways as the resulting reduction in Manning’s ‘n’ value for the hydraulic roughness enables a smaller channel section to be factored in.
A single vast Grasscrete slab provides the stability; simply put, it provides a continuously reinforced structure with none of the stability problems that can be a factor with pre-cast types. At Cobbins Brook the 150mm thick system is soiled and seeded throughout, the ribbed profile within the soil pocket helps to anchor the roots against erosion.
Given the environmentally conscious location, local demands restricted any spill or pollution into the Cobbins Brook area to protect the natural habitat alongside local fauna and flora of the area. A fast established Grasscrete cover helps maintain a green environment; the system allows natural vegetation to establish whilst at the same time performing its vital structural function.
At Cobbins Brook the access roads are also constructed of Grasscrete on two levels; on the crest and to the control structure to the embankment. The plus side is the system can be virtually trafficked immediately, with grass playing no part in the structural equation the slabs can be trafficked as soon as the concrete has cured.
There are many worldwide applications of Grasscrete in the water industry, from the remoteness of the Rufiji River in Tanzania to the suburban drain channels of Hong Kong, Grasscrete has been found to be equally at home.