Case Study

Biomanipulation Curtains

British Waterways / Canal & River Trust

Caen Hill was the last stretch of the Kennet Avon Canal (linking the River Kennet at Newbury and the River Avon at Bath) to be completed, largely because it presented such a formidable obstacle.

In all there are 29 locks which rise 237 feet in 2 miles (72 m in 3.2 km) or a 1 in 44 gradient. The locks are in three groups. The lower seven locks are spread over 1.2 km. The next sixteen locks form a steep flight in a straight line up the hillside. Because of the steepness of the terrain, the pounds between these locks are very short. As a result, 15 locks have unusually large sideways-extended pounds to store the water needed to operate them. These pounds were formerly biodiverse and species rich, however due to the increase in turbidity creating pleasure boat traffic and the rapid rise in the carp population throughout the canal network, the pounds ecology had all but expired.

High turbidity from increased diesel engine boat traffic has had a detrimental impact of the biodiversity of the Kennet Avon Canal in recent years. In January 2009 the lock pounds were drained down to facilitate fish removal.

An abundance of zooplanktivorous cyprinids (silver fish) and a few piscivores (predators) were netted from the pounds, along with turbidity creating carp to 28lb.

Silt Curtains UK installed a flexible biomanipulation curtain across the mouth of the pounds to prevent the re-entry of fish and hold back the turbidity created by boats & operation of the locks.

The flexible silt / fish curtains held back the turbidity as is clearly visible in the above image and submerged macrophytes began regenerating for the first time in many years (below).

Caen Hill Locks Biomanipulation, 17th April 2011 – Due to the success of two previous installations in 2009, the research and development department of Silt Curtains UK installed a further six curtains in lock pounds, or reservoirs, on the world famous Caen Hill flight at Devizes on the Kennet & Avon Canal.