Cobbins Brook Flood Alleviation Scheme, close to Waltham Abbey in Essex, is managed by the Environment Agency. It required an effective overspill drainage management system for its large expanse of embankment spillway.
Halcrow Group Ltd selected Grasscrete, and working closely with contractors Jackson Civil Engineering, it was installed in stages as each embankment was ready.
The system installed used 9391m2 of Grasscrete GC2 with A252 reinforcing mesh in a 150mm slab. The total installation time was 10 weeks.
At Cobbins Brook, the spillway slope is designed to handle high impact water flow from the overtopping of the embankment, up to a maximum 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.
The access roads were also constructed of Grasscrete on two levels: on the crest and on the control structure of the embankment.
The system can be trafficked almost immediately - as grass plays no part in the structural equation, the slabs can be trafficked as soon as the concrete has cured.