Otterbourne Water Treatment works is located north of Southampton in Hampshire and provides water to the east of the city. It abstracts water from the River Itchen and concern had been expressed by the Environment Agency about the potential for fish generally, and salmon smolt in particular, being drawn into the intake. Fish Guidance Systems was therefore requested to provide a system that would deflect smolt during the spring and course fish throughout the year.
The intake is typical of UK water company intakes, located on the banks of a narrow river with a water depth ranging from 1.6m in the winter to less than 1.1m in the summer. The intake comprises of four separate inlets, each 1.4m wide.
The maximum intake flow is 45 million litres per day, which represents a maximum intake velocity of only 0.1m/s, well below the recommended maximum intake velocity of 0.3m/s for 1+ fish.
The intake is located next to a public footpath, so it was necessary to ensure the system did not interfere with any users of the footpath, and the Sound Projectors were deployed in a way to minimise the possibility of vandalism.
The narrow width of the river was considered as part of the design, to ensure the system did not acoustically block the river, but the shallow water depth limited the propagation of the sound field. In order to minimise the potential for fish habituating to the signal an 8-signal Signal Generator was specified, and in order to provide feedback on the operation of the system a Diagnostics Unit was installed and linked back to the site’s main Control Room. Due to the shallow water it was recommended to install eight of FGS’s MKII 15-100 Sound Projectors to screen the intake, two in each of the intake inlets.
To safely access the Sound Projectors a walkway was installed over the top of the intake, and lockable access hatched were incorporated into the walkway to protect the system from vandalism.