Notice to Mariners - Preston And South Ribble Flood Risk Management Scheme (Phase 1 and 2)

This Notice is being issued to make Mariners aware that the essential replacement of flood defences along the River Ribble is to take place between Liverpool Road Bridge and the Ribble (Rail) Viaduct in order to reduce the flooding risk to properties in Preston and South Ribble.

The works are to be undertaken by VolkerStevin on behalf of the Environment Agency and will include:

Works description

To reduce flood risk to properties in Preston and South Ribble, approximately 500m of the stone revetment along the River Ribble will be replaced. This work consists of four separate sections: three along the north bank, and one along the south bank. The locations are shaded in green on the accompanying plan. The existing stone revetment will be replaced with a new structure to provide the necessary protection for the new flood defences. An inter-locking concrete block system called 'redi-rock' will be used to form the new revetment.

Method

A line of sheet piles will be installed along the edge of the river channel to form the bottom of the new revetments. A large excavator will be used to install the piles. Each pile will be driven into the river bed to a level of 0.5m below rock head. The piles will be 1m higher than the design level to provide protection against high tides and fluvial flooding during the works. The piles will be cut down to the finished level once the concrete works are complete. Concrete fill behind the line of piles to form a foundation for the block revetment. The pour will be in two stages to allow for a rebate for the bottom redi-rock unit to be installed.

Sealant will be applied to the pile joints to prevent any leakage of cement into the river. A concrete wagon will deliver the concrete to the required location and a pump will be used to distribute the concrete to the desired location. The redi-rock base units will be installed within the recess of the concrete foundation.

Each unit will be lifted into position with a large excavator. A number of redi-rock planting units will be installed on top of the base unit in a stepped formation. The number of units will vary depending on the height of the revetment. A perforated pipe and drainage stone will be laid along the bottom of the structure in accordance with suppliers requirements. Imported clay will be used to backfill the void between the old and new revetment which will be compacted in layers to act as a seepage cut off.

These works are licensed under the accompanying Marine Licence (L/2022/00100/1).

When will the works take place?

Accommodation works are currently underway and the main construction works will be on-going until March 2024.