Mud Mountain Inlet
Protecting the Lower White and Puyallup River Valleys
U.S. Army Corps of Engineers
Dam & Hydro
Fifty years after completing the Mud Mountain Dam, Atkinson returned to the site to make major modifications to the flow control facilities. The scope of work consisted of the construction of new intake works for the nine-foot and 23-foot-diameter tunnels, which are used to control the flow of the White River during potential flood periods.
The new intake structure, containing 29,000 cubic yards of concrete, replaced the two existing structures. Short, connecting tunnels were driven to the existing tunnels. Radial gates at the new intake replaced the Howell Bunger valves at the outlet of the 23-foot-diameter tunnel, as well as the gate at the intake of the nine-foot diameter tunnel.
The nine-foot-diameter tunnel's invert was relined with T-1 high-strength steel to reduce scouring by the large amount of gravel that is carried through the tunnel with each flood. Crews demolished the outlet works, as well as the old intakes when the new intake structure connecting the tunnels was completed.
Additionally, Atkinson constructed new pedestrian and vehicle bridges to provided operations personnel with ready access to the new inlet structure.