Fish Guidance Systems Limited

Bio-Acoustic Fish Fence (BAFF) System


BAFF systems are primarily used to guide downward migrating fish (such as salmonid smolt) away from the entrance to a water channel, so they remain in the main river, or guiding smolt from a major flow into a fish pass channel, typically at the entrance to a hydro-electric facility. The systems can also be used for other applications, including accurately blocking a river to upward migrating fish (such as for Asian Carp) or for guiding fish towards fish collection or census stations.

A BAFF system can be considered as being analogous to a conventional angled fish screen, but uses an air bubble curtain to contain a sound signal, effectively creating a “wall of sound” (an evanescent sound field) that can be used to guide fish in a river, and if required into fish passes so that the fish can pass around structures such as dams.

The sound is generated either pneumatically or electronically and is contained within the bubble curtain as a result of refraction, since the velocity of sound in a bubble-water mixture differs from that in either water or air alone. The sound level inside the bubble curtain may be as high as 170 dB re 1mPa, typically decaying to 5% of this value within 0.5-1m from the bubble sheet. It can be deployed in much the same way as a standard bubble curtain, but its effectiveness as a fish barrier is greatly enhanced by the addition of a repellent sound signal.

The characteristics of the sound signal can be completely controlled if a Sound Projector Array (SPA) system is used to provide the sound signal and further stimulus can be provided by the addition of FGS’s High Intensity Lights. This creates a BAFF system using SILAS™ technology, as successfully trialled at Head of Old River and Georgiana Slough in California, USA

FGS pneumatic BAFF systems comprise of the following components:

  • BAFF Unit
  • Air Blower or Compressor
  • Air Blower/Compressor Pipe
  • BAFF Control Unit and Control Lines


The BAFF system comprises of modular sections, each 2.4 m long, which are linked together to form the required length. The acoustic signal is entrapped in the bubbles by a driver unit and the resulting ‘wall of sound’ produces an uninterrupted guidance system.

Air Blower or Compressor

The BAFF uses an air blower or compressor to supply pressurised air to create a continuous bubble curtain, and to supply the control pressure line in the BAFF Control Unit

Air Blower/Compressor Pipe

A temperature/pressure resistant pipe delivers air from the air blower or compressor to the BAFF Control Unit and BAFF Units.

BAFF Control Equipment and Control Lines

The BAFF Control Unit is used to provide the required signal for the system by regulating the pressure in two control lines that feed the Driver Units fitted on each of the BAFF Units.  Pressure feedback lines run from the BAFF units back to the control panel to allow pressure within the BAFF to be monitored.  An alarm system indicates a sudden drop in pressure resulting from a failure in air supply.

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