Barrier Nets for Fish Guidance and Reduction of Entrainment at Water Intakes

Barrier nets have been used successfully at several sites to protect both resident and anadromous fish populations.  Two primary applications have been developed.  The first is a fish guidance application used to improve collection and transport of outmigrating Pacific salmon (Onchorhynchus spp.).  Floating Surface Collectors (FSCs) are being installed behind many high-head dams to collect juvenile Pacific salmon so they can be transported downstream to continue their outmigration.  The fish attraction currents generated by the FSCs are quite localized.  Many installations, therefore, incorporate large guidance nets to improve fish collection.  Guidance nets are composed of 3/32” to ¼” Dyneema netting and currently range in size up to 2,400 feet in length and 300 feet in depth.  The anticipated lifespan of the guidance nets are 8 to 10 years with proper maintenance.  The second application is as a physical barrier to reduce fish entrainment at spillways and water intakes.  The conservation requirements of Section 316(b) of the Clean Water Act will necessitate permits for facilities with cooling water intake structures to reduce impingement of fish and other aquatic populations.  Barrier nets provide an economical and effective physical solution to significantly reduce fish entrainment.  Barrier nets at existing installations are composed of Dyneema netting in sizes down to 1” stretch mesh.  Water velocities at several installations exceed 3.0 fps.  The anticipated lifespan of the barrier nets are 3 to 10 years depending upon the site conditions and proper maintenance.  Studies at several barrier net installations indicate that conservation requirements are being met, with fish impingement being reduced by up to 96%.  With proper engineering, installation and maintenance, barrier nets have even been successfully deployed in harsh environments such as the Great Lakes.