Overview

As part of the STARR project, the Rootlok® vegetated wall system was specified for use on part of the major Par River flood protection works to provide an innovative measure to reduce the flood risk for over 800 homes and businesses in St Blazey and Par.

Project detail

GeoGrow worked with Atkins on an early solution and then a formal design for all aspects of the installation, which was approved by the Environment Agency, Cornwall Council and Atkins.

Kier, the main contractor, placed the sub-contract order with GeoGrow to supply and install the Rootlok system over a 6-week build programme to replace approximately 44 linear metres of a failing gabion basket embankment along the Par River, situated off the A390 Tywardreath Hwy adjacent the Outboard Services and Marine Company HQ.

The first requirement was to install a dam and flume to maintain the water flow during the early part of the installation; a 600mmØ twinwall water carrier pipe extended the length of the works. Once this was in place the existing riverbed was reduced by 500mm and the old gabion baskets removed. A tie-back design was used, a reinforced earth structure including geogrids with a geogrid wraparound Rootlok bag face. Gravel-filled bags were installed on a compacted stone within the foundation and up to the average water level with the wraparound geogrid at every 3rd bag. Gravel-filled bags provide extra scour protection whilst the wraparound face offers extra factors of safety.

Once the base and foundation bags were in place, a 500mm depth of large granite stone was laid on the riverbed for extra erosion protection. At 0.75m high the wall build could continue out of the water so the dam and flume were removed to allow the river to flow naturally. Preseeded sand and soil bags where specified for use on this project, the wall was built up to an average retained height of 1.6M, the backfill area is compacted at every level to minimise any post settlement of the system.

This was a challenging project working within a water environment with restricted space and access and having to flume and dam the watercourse.