The supply of water within California is a political issue, due to the competing requirements of supplying water to over 30 million people and also irrigating over 2.3m hectares of farmland.  A network of aqueducts, diversions and other infrastructure help transfer water from one part of the state to another, and in the Central Valley of California the State Water Project (SWP) and the Central Valley Project (CVP) divert water from the Sacramento-San Joaquin Delta.

In 1992, the Central Valley Project Improvement Act made fish and wildlife protection the primary purposes of the CVP, and since then there has been increasing concern about steelhead trout (Oncorhynchus mykiss) and Chinook salmon (Oncorhyncus tshawytscha) being entrained by the diversions.

Juvenile salmon smolt migrating down the Sacramento River may take a number of routes to the ocean, however the smolt have a greater chance of survival if the stay in the Sacramento River, rather than entering one of the channels or ‘slough’ that connect the Sacramento River to the interior and Southern Delta.

This is because the predation of the smolt is increased due to the low water velocities in the interior Delta, with losses of up to 65% of the out migrating fish.  There are a number of sloughs that connect the Sacramento to the Delta, including the Delta Cross Channel and Georgiana Slough.  Since the Delta Cross Channel can be closed by a gate the main concern on the Sacramento River has concentrated on Georgiana Slough.

Modelling carried out by California Department of Water Resources (DWR) indicated that if the smolt remained in the Sacramento River side of the confluence the fish would be better protected from entrainment.  The US National Marine Fisheries Service requires the DWR to consider engineering solutions to reduce the diversion of juvenile salmonids from the Sacramento River into the interior and southern Delta and as a result the DWR reviewed the options for a Non-Physical Barrier (NPB) and requested Fish Guidance Systems (FGS) design and supply a suitable system for evaluation.

The most appropriate system available from FGS was the BioAcoustic Fish Fence (BAFF), since there was a requirement to guide the fish and keep them in the Sacramento River.  In order to provide the highest deflection efficiencies a SILAS system was proposed, so that the Non-Physical Barrier consisted of an acoustic bubble curtain, illuminated by the High Intensity Lights.

Initial trials were carried out by United States Bureau of Reclamation (USBR) in 2009 using a lab-based hydraulic scale-model and demonstrated deflection efficiencies of up to 79.9% when the barrier was operating.  Based upon these trials the decision was made to progress onto a full scale trial at Georgina Slough, with temporary installations during the Spring of 2011 and also 2012.

FGS worked with the DWR Engineers to determine the most appropriate location for the system, taking into account the swimming ability of the Chinook salmon.  Based upon a sustained swimming speed 3.4 body lengths per second, the minimum size of Chinook salmon expected at the site being 60 mm and a maximum design river velocity of 0.5 m/s, the minimum calculated barrier angle to flow was 24 degrees.  Based upon this design the maximum approach velocity perpendicular to the barrier was estimated to be 0.20 m/s.

In addition, previous research carried out at the site had demonstrated that smolt could be carried back up the main river on a flood tide and could enter Georgina Slough, even though they may have originally passed the entrance to the slough when travelling downstream.  As a result it was necessary to locate the end of the barrier sufficiently downstream to prevent this occurring.  Another requirement of the system was to ensure river traffic could continue to use the river, and so all of the components of the system were designed to be located a minimum of 3.6m below the high water level, and 2.4m below the low water level.

Access to the site was limited, and so a staging area for the installation, as well as to house the BAFF Control Equipment, air supply system and project assessment team was located on the bifurcation between the Sacramento River and Georgiana Slough.

Based upon the required barrier angle and location constraints, a barrier totalling 192m in length was specified. The sound for the BAFF was supplied by means of a Sound Projector Array based system, which enabled the optimum signal to deflect Chinook salmon to be incorporated into the system.  The Sound Projectors were located at 2m centres, and two High Intensity Light Bars were driven by each Sound Projector.

The deployment system was designed by OVIVO Water, and comprised of 16 frames, each 12m long.  Six Sound Projectors were located on each frame, with the 12 High Intensity Light Bars running along the entire length of the frame.  An FGS Power and Communication Hub was located at the centre of each frame, and connected back to the Control Equipment located on the shore, comprising a SILAS Control Unit and the Power Supply Units, which operated and monitored the performance of the entire system.  The bubble pipe ran along the front of the frames, so that the bubbles were illuminated by the High Intensity Lights, and coupled with the Sound Projectors to enable the sound to be propagated throughout the bubble curtain.

Since the system was only installed on a temporary basis each spring, temporary piles were driven into the river in order to mount the deployment frames in the required location.  The system was assembled offsite and each frame was tested before it was transported to site and installed by marine contractors and divers.

The system was assessed by tagging 1500 Chinook salmon with acoustic tags and tracking them using a 3D acoustic tracking system supplied by HTI comprising 28 hydrophones located upstream of the barrier, around the barrier itself, and also downstream of the barrier in both the Sacramento River and in Georgiana Slough.

The fish were released over a two month period approximately 9km upstream of the barrier to enable the fish to adjust to the river conditions, and the barrier was assessed with the BAFF either ‘ON’ or ‘OFF’.

The overall deflection efficiency of the system for Chinook salmon with the barrier ‘ON’ was 91%, however the conclusion of the project was that the number of fish lost down Georgiana Slough with the barrier off was less than previously thought, and so the DWR are currently reviewing other sites where the BAFF can be installed.