Sandwich Flood Alleviation Scheme

Pre-established coir pallets and rock roll mattress at base of spillway WIDE

The £21.7 million flood defence scheme involves works on 16 individual reaches of the River Stour and will reduce the risk of tidal flooding to 488 homes and 94 commercial properties in Sandwich. Client – Jackson Civil Engineering working on behalf of the Environment Agency.


VMax C350
was the product required in order to prevent soil loss from day one of installation. The VMax C350 is designed to provide a long term reinforced vegetated solution for flows up to 6 m/sec.

Salix were involved in the early design process with Halcrow (CH2M Hill) to look at scour protection of the spillways. An erosion control design software programme was used to ensure the correct product was chosen for the anticipated flow regime.

At the base of the spillways Salix Rock Roll Mattresses were installed due to the potential of hydraulic jumps.

New ditches designed to take overtopping but at the same time provide valuable habitat for water vole using Rock Rolls for scour protection and pre-established Phragmites australis Coir Pallets for instant habitat on the opposite bank. The Rock Rolls will vegetate over time and blend into the environment.

In early December the site experienced a tidal breach during the highest tidal surge in 60 years. Failure of the old defences exposed the new defences to severe conditions.

Approximately 70,000m2 of VMax C350 has been installed so far with a further 50,000m2 to be completed in 2014.

Damage to area after tidal surge with no VMax C350 protection
Damage to area after tidal surge with no VMax C350 protection

Rock mattress tie in detail at hydraulic jump zone with Vmax C350
Rock Mattress tie in detail at hydraulic jump zone with VMax C350

September installation of Vmax C350 on spillway
September installation of VMax C350 on spillway

Newly installed VMax C350 protecting slope compared to opposite bank with no protection
Newly installed VMax C350 protecting slope compared to opposite bank with no protection

Spillway January 2014 four months post installation
Spillway January 2014 four months post installation

Pre-established coir pallets and rock roll mattress at base of spillway
Pre-established Coir Pallets and Rock Roll Mattress at base of spillway