Spillway and Barrier Nets

The North Fork Hydroelectric Development is part of the Clackamas River Hydroelectric Project in northwest Oregon, which is owned and operated by Portland General Electric (PGE). The North Fork Dam is a thin-walled arch dam. Project engineers determined that a large fish collection facility in the forebay could not safely be attached to the dam. In addition, studies revealed that fish tended to congregate along the dam near the centre of the forebay. Since a fixed collector on the shore would be unlikely to attract a significant portion of downstream migrants, a Floating Surface Collector (FSC) was determined to be the best option.

To make this work, PGE contracted Pacific Netting Products (PNP) to supply a spillway net, a guidance net and its patented MultiFunction Boom™. The first step in the solution provided to PGE was to assist them with the overall design and installation of an exclusion net. This barrier is used to prevent downstream migrating fish from passing over the spillway, and instead guides kelts and smolts to a migrant channel. The guide nets, on either side of the FSC direct fish towards the facility. A unique feature of this guide net is the top portion of the barrier. The unique hydraulics of the site required a non-permeable barrier made of XR5 fabric to optimize water flow. To provide strength to fabric, this barrier is placed in front of PNP Dyneema® web and uses natural water currents for support.

KEY FEATURES

Spillway Net

  •  300 ft x 75 ft
  •  Built of 1/4” x 1/4” Dyneema® SK75 fibres
  •  Fitted with pneumatic floats to drop the net when spill reaches 4,000 cfs
  •  Excludes fish from going over the spillway
  •  Installed for year round service
  •  Minimal maintenance
  •  PNP assisted with the overall design

KEY FEATURES

Guide Net

  •  500 ft long x 75 ft deep
  •  1/4” knotless Dyneema®
  •  In-line boat passage gate
  •  Custom design to allow for drafting and servicing of the FSC
  •  20 ft raise/lower of FSC for service
  •  Dam, shore and in-lake anchors
  •  Deployed year round
  •  Anticipated lifespan: 10 years
  •  Float system with 18” x 24” hard shell foam-filled PE floats on 1” stainless cable