APEM acts as Ecological Clerk of Works for Southern Water

Before the marine engineers could begin the desilting operation, APEM was required to carry out a fish removal and relocation in the area of the river intake.

It was thought that juvenile lamprey, an eel-like jawless fish, may be living in the sediment of this part of the river. Due to their low population numbers in the UK, they are a protected species. As juvenile lamprey live in burrows during their larval stage, they could be killed by the disturbance. To prevent this, a specialist team from APEM captured and relocated the lamprey living where the screens were to be installed.

Photo of a juvenile lamprey (called an ammocoete) that was removed from the river intake before being relocated safely into another part of the river

Once the lamprey had been safely removed and relocated, the Beasley Christopher team carried out the desilting work. APEM provided an accredited Ecological Clerk of Works (ECoW) to oversee these activities. This was to check there was no impact on water quality in the local river.

The ECoW’s role was to monitor in-river conditions, focusing on the dissolved oxygen and ammonia levels around the intake area during silt removal. This is a role that APEM is experienced at undertaking having supervised desilting operations for water companies at many sites across the UK. Our teams have found that fine sediment deposits may contain high quantities of decaying leaves. Decomposing leaves can create high concentrations of ammonia.

Ammonia is toxic to aquatic life and is released into the water when silt is disturbed. This can also lower the amount of oxygen dissolved in the water. This is an issue for aquatic wildlife and plants as they need the dissolved oxygen to survive.

Throughout the works a PVC silt curtain with a chain ballast was used to prevent silt escaping. This prevented water discolouration downstream of the Smallbridge river intake.

As a result of these measures by APEM the project was a success. The river water quality was not affected by the silt removal work. Ammonia levels remained low suggesting there was no effect on water quality.

As a specialist contractor, APEM was able to use our extensive experience of desilting operations to proactively prevent any impacts caused by the activities. As a result we had a clean and hassle free operation. This experience and knowledge is vital for ensuring our wildlife and rivers are protected.