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Hydroacoustics

In October 2000, Caltrans started driving test piles for the San Francisco-Oakland Bay Bridge seismic safety project. Underwater noise pressure waves radiated from the impact driving activity, resulting in harassment and harm to listed fish. At that time, Caltrans, the Federal Highway Administration, and the National Marine Fisheries Service (NMFS) realized the need to address potential hydroacoustic impacts to fish and other aquatic species related to pile driving activities. Due to the need to develop information and research on effects criteria for fish, in 2004, Caltrans in coordination with Washington DOT, Oregon DOT, Federal Highway Administration (FHWA), National Marine Fisheries Service (NMFS), California Department of Fish & Wildlife (CDFW) and the U.S. Fish & Wildlife Service (USFWS), established the Fisheries Hydroacoustic Working Group (FHWG). In June 2008, the FHWG agreed on both peak and accumulative thresholds for fish exposed to pile driving operations.

Effects of Sound on Fish

In an effort to address hydroacoustic impacts early in the project delivery process, "Technical Guidance for Assessment and Mitigation of Hydroacoustic Effects of Pile Driving on Fish", has been updated. The Compendium of Hydroacoustic Data is available in Appendix 1 of the Manual. Please continue to work with appropriate project delivery team members and resource agency staff to address issues specific to your project and to check the fish hydroacoustic website for changes as science and engineering evolve to further address hydroacoustic issues. For biological information and assistance regarding hydroacoustic impacts please contact Melinda Molnar or Jimmy Walth.

Caltrans has developed the Hydroacoustic Biological Assessment Guidance for use when preparing the consultation analysis.

Design of bridge foundations in seismically active zones has necessitated the use of steel piles. In addition to the superior structural properties of steel piles under seismic loading, steel piles address a number of other attendant foundation issues. Steel piles are cost effective (concrete pile cast within a steel shell), minimize bridge foundation scouring, armor the structural elements from inadvertent collisions with marine traffic, and minimize the "footprint" within the aquatic environment. Aging transportation infrastructure and the need to service transportation demand have increased the number of bridge projects that require pile driving. As a consequence of larger piles and required retrofitting activities, pile driving for bridge projects has resulted in the observed death of fish in San Francisco Bay.

Human-related activities have historically contributed to the decline of fish populations and resulted in the listing of fish species under the federal ESA. Nearly every estuary and major stream in California, Oregon, and Washington provide habitat for one or more listed fish species and species managed under the Essential Fish Habitat (EFH) provisions of the Magnuson-Stevens Act (MSA). The observed death of fish associated with driving large diameter (greater than 5 foot) steel shell piles has elevated the public and resource agency concern relative to effects on listed species populations. Required development of minimization measures to protect fish species listed under the federal Endangered Species Act (ESA) has resulted in costly project delays and increased project implementation costs for departments of transportation in California, Washington, and Oregon.

The FHWG met in June 2008 and agreed to an interim criteria (PDF) for injury to fish from pile driving noise. This new criteria is to be used as of August 2008 until further notice. This is a dual criteria including a peak level of 206 dB (peak) AND a cumulative SEL level of 187 dB (SEL) for fish 2 grams and heavier OR a cumulative SEL of 183 dB (SEL) for fish smaller than 2 grams.