The Valdez Star - Serving Prince William Sound and Copper River Basin

By Lee Revis
Editor, Valdez Star 

Minimal flooding this year after ice damn breaks on Valdez Glacier

Officials were prepared after many years of seasonal high waters in the area

 


Seasonal flooding of the Glacier Stream was minimal this year - though the city and other government agencies were on high alert.

In late June, the City of Valdez issued an alert through its public information office, warning area users that an ice dam on the Valdez Glacier was threatening to overflow, following a potential flood warning it received from the Alaska Division of Geological and Geophysical Surveys (DGGS).

On July 11, Allie Ferko, the city's public information officer, issued a statement that said the damn had burst and that immanent danger had passed.

According to a report issued by Alaska Department of Natural Resources and released by the city, this year's outburst was smaller than has been seen in recent years.

"We monitored the water level in Valdez Glacier Lake where USGS (United State Geological Survey) has installed a gage, and observed a daily increase of water levels of 1 foot per day, starting on June 25th and lasting through the 28th," the report said.

In the last two years, flooding from the lake has overwhelmed culverts running towards the Richardson Highway next to the dump road and waters have overrun the bike path in the area, and caused minor flooding on the dirt road across the highway leading into Old Town.

In past years, the Glacier Stream has cut into the Dump Road, and threatened to eat into the city's landfill. It has also run dangerously close to the historic gold rush era cemetery and caused very high waters to settle on the dirt roads that lead to the Old Valdez town site.

While the expected June flooding was minimal this year, the area typically also sees high waters and/or flooding in the late summer or early fall.

"One outburst event usually occurs in June as a result of snowmelt and one event usually occurs in September-October as a result of glacier meltwater and heavy precipitation (rain)," the report says.

The City of Valdez has for many years worked on flood mitigation plans for the areas downstream from the glacier, as well as other areas prone to flooding, including the subdivision in the 10 Mile area and Mineral Creek.

This year's overflow from the lake was spotted by a helicopter tour operator.

DNR says the lake was created by an ice dam at an altitude of approximately 220 feet adjacent to the Valdez Glacier.

Photo courtesy City of Valdez

Water level of the ice-dammed Valdez Glacier Lake before the outburst in late June.

"We believe that the lake was initially formed as a pro-glacial lake of a tributary glacier (unnamed) to Tonsina Glacier which has significantly retreated," the report says. "Valdez Glacier ice-dammed lake has bi-annual outburst floods of varying magnitude."

The exact cause is unknown.

"The exact dynamics of each outburst event is currently unknown, but we believe that it is a combination of water pressure building up as the lake volume increases and sudden expansion of conduits (englacial channels) within Valdez Glacier that enable water to be transported downstream sub-glacially," DNR said. "The water exits the glacier into Valdez Glacier Lake with the potential of flooding of the pro-glacial lake itself and the Valdez Glacier Stream."

 

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