The material, engineering, and technology of structures and systems used to guide fish to a particular point, or exclude them from moving through a dam or into a cooling water intake has changed dramatically in the past 10 years. Fish passage structures at Baker Lake, Washington (Puget Sound Energy), and North Fork Clackamas, Oregon (PGE) have shown tremendous success in passing fish at high head dams.  Exclusion nets like the 2 ½ mile long barrier at Consumers Energy in Ludington MI or the barrier net at Elkhead Lake, Colorado (6,355 ft elevation) have helped prevent the passage of non-native fish or prevent entrainment of valuable species in generations facilities. The lessons learned from 25 years of installations, the advancement of methods and techniques, the findings and results of fish passage, or fish exclusion efficiencies have been published in studies and reports used for regulatory compliance, fisheries management, and scientific research.

As all stakeholders understand, the multiple benefits of harnessing our rivers include; the generation of clean, affordable, and reliable electricity; storage of water for irrigation or human consumption; flood control, and recreational activities. And we all understand the need to balance the impact of these structures against the needs of river connectivity including the ecology of our waterways, and the fish and animals that live in the environments.  

Since the time of the ancients, physical methods using materials including rocks and wood, or behavioral methods, including sound and motion have been used to corral or trap fish. Today, at weirs and low head dams, river connectivity solutions include a wide variety of fish passes from pool and weir passage, rock ramp passes to bypass channels. However, downstream fish passage at high head dams presents unique challenges. 

Fibers developed in the last 100 years, such as nylon, Dacron, or polyester) and types design and construction of nets used in commercial and recreational fishing (Gill, Trawl, Purse Seine), seemed logical but proved impractical to use in permanent or semi-permanent installations and dams and energy facilities. Fish, debris and aquatic growth did not need to be caught or collected; they needed to be guided or excluded. The shape and function of the net would need to be deployed and maintained at all pool levels over a long period of time to be cost-effective.

Dam safety and operational efficiency personnel required a material with the highest strength possible and lowest amount of surface area; loads and stress from water required a material with excellent fatigue resistance. To be cost-effective the material should have excellent resistance to decay, be hydrophobic, and resist adhesion of marine growth. To be safe, the material would need to have a very low stretch. Fish biologists and regulators required a material with a smooth surface that would result in less damage to the fish and marine life while maintaining a consistent shape of a small size mesh to prevent small fish from passing through the net.

In 1997, Pacific Netting Products, partnered with DSM, and started to develop applications for use of a new material in the hydroelectric industry, Dyneema. The Dutch multinational, DSM, invented this ultra-high molecular weight, low density, highly crystalline linear polyethylene which became commercially available in the early 1990s.

Guidance and Exclusion Nets 1When used as a netting material, this polymer provides exceptional strength and performance. With a strength is equal or better than high-quality steel wire ropes the same diameter, this lightweight, low profile, low drag material has excellent flex fatigue to address the constant motion, biostability, and softness. The material is suitable for both the hydrological and biological needs of fish passage engineers and dam operators.  One National Marine Fishery Service biologist, talking about the performance of these nets said: "they act as an extension of the shoreline, they guide the fish to where we want them to go”.

Today this fiber is used in many applications, from personal & vehicle armor to medical applications such as small joint sutures or orthopedic applications. In the fish guidance sector, PNP nets are providing customers solutions expect to last 15 years or longer. Custom designed for each site, these installations are cost effective and can be low maintenance. Ask for our statement of qualifications or visit our projects page for more information about how PNP can assist you in balancing our human needs and our environmental needs of our rivers and waters.

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