Report: Constricted river channel contributed to town of Pacific's flooding

Substantial changes in the depth of the White River contributed to flooding in the city of Pacific last January, but poor communications between King County and the operator of a dam upstream made a bad situation worse.

Those are some of the conclusions reached by a group of 28 officials who met weeks after the release of water from Mud Mountain Dam on Jan. 8 caused widespread flooding in Pacific, a city of 6,000 in South King County.

"The apparent cause of the increased flooding is a substantial change in channel capacity," according to a summary released today by the U.S. Army Corps of Engineer (USACE), which operates the dam.

The summary noted that the river had lost about 30 percent of its capacity at one location below the Mud Mountain Dam. As a result, the Corps miscalculated the amount of water it could release from the dam without causing serious flooding downstream.

The flood caused $15 million in damages to 112 residences and 10 commercial properties, the report noted.

To prevent future problems, the Corps said it would explore adding gauges and other technology that will allow it to better determine the water levels on the White River.

Among other things, it also will train spotters who can be dispatched on the ground to provide firsthand accounts of the situation, and will work to improve communication with local governments.

"The feedback loop from the local communities back to the USACE is considered broken," the summary stated. "Although improved communication and feedback may not have prevented flooding in Pacific as a result of the January 2009 event, it likely would have reduced the duration by facilitating the management of the flood event differently at Pacific."

The Corps was notified of the flooding, according to the summary, but the notification consisted of a phone message that " 'the water in the White River at Pacific is a little higher than normal.' No sense of urgency was communicated at any level and thus no immediate action was thought necessary."

The summary, which was released by the Corps' Seattle district commander, called for "common language" and standards so that everyone has a shared understanding of the situation.