Elwha River

Elwha River

Background:

The Elwha River dam removal project, which included the removal of the Elwha and Glines Canyon Dams during 2011 to 2014, was the world’s largest dam removal and restoration project at the time. The objective of the project was to restore fish passage to upstream areas, reconnect watershed sediments and wood loads, rebuild coastal beaches, and restore Elwha Tribe cultural areas. During the 84-year average operational period for the two dams, the combined accumulation was estimated to be approximately 27 million cubic yards of sand/gravel/cobble and silt/clay - the majority of which moved downstream over the months and years following dam removal. The Elwha Surface Water Intake diverts water from the Elwha River downstream of both dams and was subject to extreme sediment related impacts resulting in an airburst-cleaned cylindrical wedge wire T screen system being completely inundated with sediment resulting in the need to redesign and refurbish the screen system.

ISI was hired to redesign the screen system and developed a vertical wedge wire drum screen system with mechanical brush cleaning system, water jetting, repurposed airburst system, and screen base designed to raise the screens off the river bottom and convey rather than settle sediment within the base piping through use of high water velocities. The screen system includes six D60-36HA-F wedge wire drum screens which measure 60 inches (1524-mm) in diameter and 36-inches (914-mm) tall. The screens have a 1.75-mm slot opening and 50 percent open area to provide 18.8 cfs (12.2 MGD; 1,916 m3/h) per screen when fully submerged at an approach velocity of 0.4 fps. The brush cleaning system includes a hydraulic drive assembly to rotate the screens between internal and external brushes. The total screen system capacity is 112.8 cfs (73.2 MGD; 11,496 m3/h).

Benefit of ISI System

ISI's Elwha River screen system includes the following key features and benefits to address the challenging site conditions:

1. The vertical orientation of the wedge wire drum eliminates the potential to accumulate sediment inside the screen.
2. The metal base structure was designed to maintain high velocities and therefore not accumulate sediment and also keep the wedge wire screen high in the water column away from bottom sediment.
3. The jetting system and repurposed airburst system resuspend sediment that may accumulate around the base of the screen and allow the flow of the river to move it downstream.
4. A debris deflector was installed upstream of the screens to divert large woody debris from the screen area.

Owner:

City of Port Angeles

Engineer(s):

Intake Screens, Inc.

General Contractor:

Macnak Construction, LLC

Location:

Elwha River, Port Angeles, WA