Dam Safety 2018: Mud Mountain Dam Field Trip

This field trip has filled to capacity and registration for it has now closed. To be placed on a waiting list, please email ASDSO. If there are any cancellations, we will offer open seats to individuals on the list.

When: Thursday, September 13; 8:00 am - 4:15 pm 

Registration Fees: $95 per person includes motorcoach transportation, guided facility tours, box lunch and beverages.

Background & Project Overview: Mud Mountain Dam is a critical flood risk management project of the United States Army Corps of Engineers, Seattle District. Completed in 1948, after the establishment of the 1936 Flood risk management Act, it is a 432 foot tall earth embankment dam in a narrow canyon on the White River on the boundary between King and Pierce Counties in Washington State.

The embankment itself is a rock-fill dam with concrete cutoff wall in an earth core with a crest elevation of 1,257 feet. The width at the base of the embankment is 1600 feet which tapers off to 25 feet at the crest. The 1,200 long spillway has a capacity of moving 245,000 cubic feet of water per second and is designed as an uncontrolled chute to protect the dam in the event a flood risks overtopping the embankment. The intake and tunnel structures include a 9-foot (sediment bypass tunnel) and 23-foot (fish and flood flow passage tunnel). The tunnels are design to pass normal river flows through the project (averaging 1,429 cubic feet per second) to include any sediment bed load and downstream fish passage as juvenile fish migrate to the Puget Sound.

While only used for flood management, the project reservoir area stretches 5.5 miles upstream of the dam and is capable of storing 106,000 acre-feet or 34.5 billion gallons of water. The project provides essential flood risk management to many commercial, and residential neighborhoods throughout the southern Puget Sound region, as well as critical industries such as lumber and wood processing, aircraft production, tech industry (including critical Amazon server farms), heavy warehousing, agriculture, and port facilities in Tacoma. The total population protected by the dam is approximately 278,000 and includes the cities of Buckley, Enumclaw, Sumner, Puyallup, and Tacoma. The project also includes year-round day-use recreational facilities to include play structures, picnic shelters, two viewing decks, the only wading pool in the USACE inventory, and miles of trails throughout the land surrounding the reservoir.

Since initial construction, the project has undergone several major improvements including: construction of a concrete cut off wall in 1990’s (the deepest concrete cutoff wall on earth at the time) to reduce risk from internal erosion, raising the spillway chute walls in 1992 to accommodate the revised inflow design flood, construction of a new outlet works facility in 1995 to reduce risk from seismic hazards, and lining of the outlet tunnels in 2000 with steel plate to protect against bedload erosion. Construction is currently in progress to replace the 9-foot tunnel’s damaged steel invert liner, and construction has begun to replace the Buckley diversion/fish trap structure located several miles downstream with a state of the art fish passage facility to be owned and operated by the Corps.

The horseshoe shaped sediment bypass tunnel (9-foot tunnel) was designed to pass normal river flows and sediment bed load derived from the slopes of Mt Rainier, and therefore experiences severe abrasion damage from materials ranging from glacial flour to boulders up to 20 inches in diameter. The original, 800-foot-long concrete-lined, 9-foot horseshoe shaped tunnel had 40-pound ASCE and ARA rails lining the concave shaped invert. This design required repairs every two to three years from the beginning of project operations. In conjunction with the intake tower replacement in 1995, major changes were made to the 9-foot tunnel. The 9-foot radius of the horseshoe invert was replaced with a flat invert; the tunnel entrance, new floor, and portions of the walls were lined with 1-inch thick steel plate. In August 2006 approximately 11 years after the new steel liner was installed, five holes in the steel liner were discovered while the 9-foot tunnel was dewatered for inspection varying in size from 6 inches to 18 inches in length, and had completely worn through the 1-inch steel liner, exposing and eroding the underlying concrete. A design–build contract to repair the tunnel liner was awarded in September 2016 to Garney Companies, Inc. The Corps contract specified a replaceable steel liner design. Garney, utilizing the value engineering (VE) process, successfully proposed a granite block liner design. The granite liner, when complete, will be a one of a kind repair in the U.S. and is predicted to last up to four times longer than 1-inch steel plate (at similar cost) before requiring repair resulting in significantly reduced maintenance costs. Construction of the new tunnel liner began in July of 2017.

Since construction, the dam has been an added barrier to fish migration. Adult salmon have been collected at the downstream Buckley diversion/fish trap structure (owned by Cascade Water Alliance) since 1941 and transported upstream of the dam to a release area owned by the Corps. The current fish trap is 62 years old and the barrier structure was built in the early 1900s. The project has undergone numerous downstream fish passage studies resulting in effective strategies that help juvenile fish pass through the project as well as to improve the collection and transportation of migration adults. To replace the aging structure, the USACE Seattle District invested $112 million in 2018 to construct the nation’s largest fish trap and sorting facility in the nation at the Buckley site. This innovative, highly modernized facility will greatly improve the trap and haul operation allowing up to 1.2 million fish to safely pass the project each year.

Itinerary:

8:00 am Motor coach (approx. 50 people) departs Washington State Convention Center

9:30 am Arrive at MMD. Attendees divided into two groups of up to 25.

  • Group 1 in 4x4 vehicles: Guided tours of the one-of-a kind granite block armored sediment bypass tunnel (in construction), the outlet works from the deck atop the 140 foot tall trashrack tower, the spillway, and the dam crest/embankment concrete cutoff wall.
  • Group 2 in tour bus: Guided tour with project history and operations discussion, and visits to both the dam vista overlook and the restricted access pedestrian bridge to the outlet works air shaft tower (365 feet above the river bed).

11:00 am Attendees divided into two groups of up to 25.

  • Group 1 in tour bus: Guided tour with project history and operations discussion, and visits to both the dam vista overlook and the restricted access pedestrian bridge to the outlet works air shaft tower (365 feet above the river bed).
  • Group 2 in 4x4 vehicles: Guided tours of the one-of-a kind granite block armored sediment bypass tunnel (in construction), the outlet works from the deck atop the 140 foot tall trashrack tower, the spillway, and the dam crest/embankment concrete cutoff wall.

12:30 pm Entire tour group to re-convene for lunch in the picnic shelter

1:30 pm Depart for Mud Mountain Dam Fish Passage Facility (FPF)

2:00 pm View FPF construction and attend briefing and Q&A session on the history, design and construction of the largest trap-and-haul FPF in the US.

2:45 pm Depart MMD FFP

4:15 pm Motor coach arrives at Washington State Convention Center

Safety and Security Requirements: 

This tour includes some physical activity, including the climbing scaffolding style stairs to access the tunnel. In addition, since this tour includes two active construction areas (sediment bypass tunnel and the fish passage facility), the following personal protective equipment (PPE) is required for each participant:

  • Hard hat
  • Safety vest
  • Safety glasses*
  • Steel toed boots*

The USACE Seattle District will be able to provide hard hats and safety vests for those participants who are unable to bring their own. However, *attendees are required to bring your own safety glasses and steel toed boots for the tour. By registering for this activity, you are agreeing to arrive prepared for the tour with safety glasses and steel toed boots. Attendees who arrive without these items will not be permitted to board the bus.

The USACE security protocol requires that all attendees carry a photo id with them. There are additional requirements for foreign nationals (non-US citizens). Please indicate your status on the registration form so that all security requirements can be met in advance of the tour.

Special thanks to our sustaining members