While the U.S. Army Corps of Engineers is assisting with the short-term needs of communities affected by spring flooding along the Yukon River, it is also taking steps to mitigate future risk.
Alakanuk, Circle, Eagle, Emmonak, Fort Yukon, Galena and Hughes flooded when ice jams created rising waters, which destroyed buildings and caused residents to evacuate their homes.
After the president declared the flood-affected areas a federal disaster June 25, the Federal Emergency Management Agency joined the State of Alaska already on the scene providing emergency response. FEMA reached out to the Corps to leverage its experience and expertise.
The Corps initially sent two assistant team leaders from a national cadre for the emergency support function of public works and engineering to serve in the Anchorage Joint Field Office. They identified mission requirements, and coordinated with FEMA and the state to determine which personnel were needed.
They turned to the Corps’ Headquarters and Pacific Ocean Division to identify and assign experts who would deploy to Alaska.
“Considering the short construction season and federally-declared disaster, this is a critical mission for the Pacific Ocean Division and Alaska District,” said Dave Spence, chief of the Alaska District Emergency Management Office.
The most immediate concern was housing.
Operating from the joint field office, three Corps employees are helping to manage short-term housing needs, construction costs, contractor mobilization and productivity, as well as reporting progress on two Corps technical assignments for Galena.
Working with experts on housing, utilities and debris removal from the Huntington and Memphis districts, the goal is to enable displaced residents to return to a home in their villages before winter, said Tina McMaster-Goering. She temporarily vacated her job as a project manager in the Alaska District Civil Works Branch to oversee the tactical housing group.
Her team tracks activities related to the repairs of damaged housing in support of FEMA’s program to aid eligible homeowners. As needs evolve, the latest mission assigned to the Corps is construction project coordination.
“The challenge is to get the materials delivered to these communities,” McMaster-Goering said. “(The work) has been really interesting and rewarding. You feel a sense of accomplishment on a day-to-day basis. It’s amazing to see the caliber of (Corps employees) who deploy to assist with these jobs.”
Nearly 90 percent of Galena’s buildings were destroyed and most of the community’s 400 residents left their homes.
More than helping residents to return to their homes, the Corps completed two studies useful in avoiding rebuilding in restricted areas of the flood zone.
The state asked the district to identify high water marks during the flood. Weeks later, the Corps returned during the recovery to survey the observed high water level to use for flood height records and comparisons for a baseline structure elevation study.
The Corps completed a first floor flood elevation survey for 318 buildings listed by FEMA and established new vertical benchmarks throughout the community.
In the past, the community’s benchmark was located five miles away at the airport, which is adjacent to the village. The new benchmarks will now allow the community quicker access to a vertical control and to accurately measure the appropriate height during construction, said Tom Sloan, Geomatics Section chief.
“Some of these houses were up on blocks when we surveyed them. Regardless, we still noted the elevation at the time of the survey,” Sloan said.
Finding the flood level that has a 1 percent chance on average of occurring in any given year (100-year flood) on the ice-affected river was the job of the Alaska District Hydraulics and Hydrology Section in collaboration with the Corps’ Cold Regions Research and Engineering Laboratory.
They studied the ice-affected flood stage frequency. The challenge is that unlike open-water events, flooding as a result of an ice jam is usually site-specific and unpredictable. It may reach peak stage at a fraction of the discharge of an equivalent open-water peak, according to a 2011 Corps of Engineers report on the topic.
At Galena, ice blockages typically form at a spot called Bishop Rock, 18 river miles downstream. Now there is technical data to determine the flood stage frequency and water level, said Ken Eisses, chief of the Hydraulics and Hydrology Section.
The estimated elevation of the 100-year flood at the National Weather Service river gauge is 135.5 feet, which is 11.5 feet above flood stage. The Corps recommended that first floor elevations of all structures be placed at least 1 foot, or as much as determined by local and/or state officials, above that height.
Just as members of Alaska District’s Hydraulics and Hydrology Section were integral to the flood response and recovery, so were engineers in the Geotechnical and Materials Section.
Although the airport levee held the flood water, the chance of a failure in years ahead was enough to justify a complete structural assessment. Engineers inspected it initially during the flood upon request of the state to identify deficiencies.
“There was distress on the levee during this flood event,” said James Sauceda, chief of the Geotechnical and Engineering Services Branch. “Because of this distress, the structural integrity of the levee needs to be evaluated since it protects the runway, which is the community’s lifeline.”
Under Corps technical oversight, Dowl HKM and Golder Associates were contracted to first perform a topographical survey and then a geotechnical investigation of the levee.
The topographical survey will provide surface contours of the levee area with cross-sections of the distressed areas to allow engineers to examine its condition. The geotechnical investigation will consist of a data review and site visit coupled with a subsurface exploration and laboratory testing program to characterize and analyze the subsurface conditions.
Analysis will primarily focus on erosion, seepage and slope stability. At the completion of the geotechnical investigation, a report will be provided and include short and long-term mitigation recommendations as warranted, Sauceda said.
“Historically, they experience flood events frequently,” he said. “Nothing says that it can’t happen again next year.”
He added that the Alaska District contracting office has been highly supportive in taking on these additional duties while the contractors are performing very well under less than ideal circumstances.
“The working conditions in Galena are tough, but we are doing it. The team is pulling through,” Sauceda said.
Emergency support function personnel returned to their home stations after most of their missions were complete. The Alaska District Emergency Management Office assumed management of the remaining activities.
About 25 Corps employees participated in the FEMA mission this season. The last time the Corps was involved in emergency flood response was in 2009 for the village of Eagle. Teams traveled to survey the site, assist with debris removal and help restore critical public facilities.