On July 15, 1976, a release of water from the Mud Mountain Dam and a Puget Power diversion dam sends a surge of water roaring down the White River. Moving at six miles per hour, the five-foot high wall of water churns downstream where it inundates two children, drowning them. The body of 9-year-old Karen Mason is recovered 10 days later, and that of 10-year-old Cathy Avila is found on July 26.
White River System
Mud Mountain Dam is located seven miles southeast of Enumclaw, situated in a deep, narrow canyon of the White River. When it was built in 1948, it was the largest earth and rock dam in the world. The dam was built for flood control, and its reservoir is usually empty except for the normal flow of the river.
Five miles downstream from Mud Mountain Dam is a Puget Power diversion dam, which shunts water to Lake Tapps in Pierce County, and also powers a 63,000-kilowatt powerhouse. Built in 1911, the dam is a wood crib structure filled with rock. Removable “flashboards” keep water seven feet above the dam, and can be removed in a flood situation.
Since it is costly to have silt enter the Puget Power flume, crews can remove the flashboards when needed to divert excessively silt-laden water from the settling basin. Once the flashboards are removed they cannot easily be replaced.
The White River flows around Lake Tapps (in the old Stuck River channel) and eventually joins the Puyallup River near Sumner in Pierce County. From there it flows into Commencement Bay near Tacoma.
Releasing surplus water from the Mud Mountain Dam is a routine task, done to clean silt and debris from the reservoir. On July 14, operators at the dam alerted Puget Power operators that a release would occur the next day. At 8:05 a.m., on the morning of July 15, they phoned again, notifying the downstream dam that the series of discharges would increase the flow by approximately 750 cubic feet per second each.
Beginning at 8:35 a.m., the discharge was released in three stages over a 10 minute period, for a total increase of 2,638 cubic feet per second. The Mud Mountain crew went on to other tasks. Two miles below the dam, the river rose by 8.4 inches.
Ten minutes later, Puget Power operators spotted muddy water coming downstream. They decided to close the flume gates and remove seven of the flashboards to keep out the silt. By doing so, another 1,750 cubic feet per second was added to the river’s flow. At 9:15, they finished and continued on with other duties. As they walked away they heard the roar coming toward their dam from upstream, and assumed that the situation was normal.
What they did not know was that the combined release of water had caused the river to blast forward at an unprecedented rate of six miles per hour. Downstream from the Puget Power operations, a wall of water churned its way through the narrow gorge, seen by no one. The roiling mass carried with it dirt, rocks, logs, and other debris.
The weather that day was typical for summer -- hot and humid. Near Pacific, a small town south of Auburn, a group of children played on a gravel bar alongside the river. The seven children were supervised by two adult women as they frolicked in the ankle deep water. Unbeknownst to them all, a juggernaut was heading their way.
After shooting through the narrow canyons upstream, the surge of water was now five feet high, and filled with detritus. It reached the town of Pacific at 1:30 in the afternoon. As the wall of water approached the gravel bar, the two women saw the wave and ran screaming into the river to save the children. Five youngsters made it out with their help.
One of the rescuers, Linda Fitzgerald, was swept off of her feet as she frantically tried to save the last two children. She was carried 400 feet downstream and became badly bruised, but by the time she regained her bearings, the little girls were lost, caught up in the flash flood.
Nine-year-old Karen Mason was found dead in the Puyallup River 10 days later, and the body of 10-year-old Cathy Avila was found floating face-down near Commencement Bay, the day after that.
The state Department of Ecology stepped in to investigate. Director John Biggs stated, “I’m not sure we had the authority to do this investigation, but since no one else was doing anything, we sort of assumed the authority.”
Six weeks later, they released their report. They found that there was no coordination operation between the two dams, and that the safety of downstream users was not considered when the water was released. They also faulted the design and process of operations at both aging dams. It was also discovered that the gravel bar that the children were playing upon had been scheduled for removal, but the project had become mired in red tape.
Based on these findings, changes were made so that water releases of this scale would not happen again.