Project Description
Barrow Haven was famous for its clay bricks and tiles recovered from the edges of the Humber estuary. Flooding was a regular event amongst the workers’ cottages and the tidal surges that affect the Humber estuary are greater today than the disastrous floods of February 1953. Since then extensive defence work has been undertaken, but Barrow Haven continues to suffer and in one instance it is estimated to have caused flooding of around 2,600 properties. Key to the defence works is the protection of freshwater lagoons adjacent to the flood defences. These lagoons are supplied by underground springs to provide a fishery and irrigation ponds for local agricultural land. Once seawater enters the lagoons they become contaminated with sea water, rendering them useless for several years.
The Environment Agency committed £650,000 to these risk based repairs along the south bank of the Humber, prioritising Barrow Haven in line with the Humber Flood Risk Management Strategy.
The Challenge
The works consisted of filling breaches in the existing flood embankment using clay as a core, with compacted earth either side using varying gradients on the back face of typically at 1:2, and occasionally 1:1. The crest was raised along the full 600m length to allow for rising tide levels, reducing the likelihood of overtopping in a storm event. The challenge was to protect the back face of the embankment during flood events where water accelerates to 4m/s, with additional “slug” overtopping waves which are generated across the wide estuary potentially accelerating flow to 6m/s.
Whilst well established grass can withstand a certain flow for a period of time, without reinforcement it is prone to weak spots resulting in damaging erosion issues.
The Solution
ABG Erosamat 3/20Z 500M was chosen by Halcrow as an open three-dimensional turf reinforcement mat anchored firmly at the top and bottom of the back face. Erosamat erosion control matting acts to mitigate the damaging effects of surface erosion in flood events. Grass roots entwine with the Erosamat to provide anchorage and has been proven in high flow environments to extend the design flow event to many times more than unreinforced grass.
Erosamat Type 3 Erosion Control Matting
The ABG Service
ABG supplied technical advice on the limiting velocities, anchorage and pinning details for the design along with site assistance.
