Southern Water appointed APEM Ltd to provide environmental monitoring and Ecological Clerk of Works services at the Smallbridge Pumping Station site in Kent. The aim of this project was to allow new screens to be set up at the river intake on the River Teise without causing damage to fish or affecting water quality.

To enable the installation of the screens, silt needed to be removed from this river section. APEM worked in partnership with Beasley Christopher Ltd to carry out the works.

Juvenile lamprey, a protected species, were living within the sediment at the river intake. During their larval stage this species live in burrows in the river bed. Any desilting work would likely kill the lamprey. To prevent this, a specialist team from APEM worked to capture and relocate any lamprey from in front of the intake screens. The Beasley Christopher team then carried out the desilting work. APEM provided an accredited Ecological Clerk of Works (ECoW) to oversee activities, ensuring there was no impact on water quality in the local river, the River Teise.

Acting as ECoW, APEM’s role was to monitor in-river conditions. This focused on dissolved oxygen and ammonia concentrations in and around the intake area during the silt removal operation. APEM is experienced at supervising desilting operations having undertaken them for water companies on many sites across the UK. We have found that fine sediment deposits may contain high quantities of decomposing leaves which can produce high concentrations of ammonia. Ammonia is highly toxic to aquatic life and is released into the water when silt is disturbed. This can also lower the concentration of oxygen dissolved in the water.

The river intake area at Smallbridge was enclosed by a PVC silt curtain with chain ballast during the operation to avoid any significant water discolouration or pollution in the river downstream.

The Results

  • Water quality in the river was not impacted by the silt removal work.
  • All of the values for ammonia were also at very low levels and indicate no adverse effect to water quality.
  • This project demonstrates the value of using specialist contractors with experience of desilting operations to avoid causing problems in rivers such as pollution and harm to wildlife.