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Engineers measure snowpack to predict flooding

Lauren Oliver measuring snowpack
USACE - Alaska District
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Lauren Oliver, civil engineer in the district’s Hydraulics and Hydrology Section, begins to take measurements at one of the telemetry sites in the Chena River basin April 30. The U.S. Army Corps of Engineers – Alaska District partners with the U.S. Department of Agriculture’s Natural Resources Conservation Service to measure winter snowfall levels and collect additional data from nine monitoring stations in the Chena River basin. The agencies analyze this information to estimate the volume of runoff when the snowpack melts in the mountains.

USACE monitors flood risk from breakup conditions in Chena River basin after record snow/rain events last winter.

As you have been hearing, a Flood Advisory is now in effect through this (Monday) morning for the Chena River near North Pole and upstream to its headwaters. There is also a Flood Watch on the Salcha River.

River levels on the Upper Chena rose gradually over the weekend, and the National Weather Service is reporting minor flooding of low-lying or flood-prone areas including along Chena Hot Springs Road, and the Steamboat Landing area in North Pole. The latest river forecasts are at weather.gov/aprfc.

The U.S. Army Corps of Engineers – Alaska District regulate streamflow on the Chena by operating Moose Creek Dam at the Chena River Lakes Flood Control Project in North Pole.

USACE, partnered with the U.S. Department of Agriculture’s Natural Resources Conservation Service, uses snow survey data to forecast potential flooding during breakup, collecting data from nine monitoring stations in the Chena River basin. That’s how they estimate the volume of water when the snowpack melts in the mountains… so they can anticipate when to bring down the gates in the dam and prevent flooding downstream in Fairbanks.

Chena River in April
Lauren Oliver
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USACE – Alaska District
The Chena River snakes through downtown Fairbanks at dusk April 30, 2022.

After the 1967 flood of Fairbanks that caused about $80 million in damages, the Chena Project was constructed in the 1970s to protect the city, North Pole and Fort Wainwright from future disasters.

Although the floodplain behind the dam remains dry for most of the year, USACE officials may impound water when the river level runs high because of significant melting snow, ice jams or heavy rains. Since it was constructed, the 7 ½ mile earthen dam has operated 30 times.

Rosie Duncan, a USACE employee who participated in the snow survey work, says the Fairbanks area is still feeling the effects of the record snowfall and freezing rain event from December.

Chena River basin
Rosie Duncan
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USACE
An aerial image of the Chena River basin near Pleasant Valley and Munson Ridge on March 30, 2022.

Nathan Epps, chief of the Hydraulics and Hydrology Section, says “Snow surveys measured about double the normal Snow-Water equivalent in the Chena’s watershed, which is the highest recorded since measurements started in 1980.”

During normal operations, Moose Creek Dam regulates the flow of the Chena River at a rate of no more than 12,000 cubic feet per second in downtown Fairbanks.

Downstream flood effects along the river also depend on conditions in the Tanana and Little Chena rivers as well as local drainages. Low-lying areas near the Chena River may experience minor flooding, while elevated groundwater can occur for several thousand feet downstream of the dam.

Mega Project

Meanwhile, construction will begin this spring to reinforce the structure. Referred to as a “mega project” and funded by the recently enacted Infrastructure Investment and Jobs Act, the Bauer Foundation Corp. of Florida was awarded a $75.5 million contract to establish a mix-in-place concrete barrier wall at the base of dam that spans 6,200 linear feet at depths of up to 65 feet.

The project stems from a 2017 modification study that recommended reinforcement of the dam to extend its life and enhance protection of the greater Fairbanks region for many years to come. Construction is anticipated to be complete by January 2026. The dam will continue to operate and regulate the flow of the Chena River as needed while work is underway.

“The successful completion of this modification project will allow us to address risks associated with aging infrastructure and deliver upgraded infrastructure that is built to last,” DeRocchi said.

The public is encouraged to stay informed of weather and flood conditions by monitoring news reports and social media posts. It also is recommended that people remove belongings from low-lying areas, such as basements and crawl spaces, to protect these items from potential flood damage.

As USACE prepares for a busy spring that may involve operating Moose Creek Dam to reduce flood risks and making safety improvements to the structure itself, local citizens can be assured that the team has their best interest in mind.

“Public safety is always our top priority,” DeRocchi said.