USGS measures glacial flooding in Juneau, Alaska

(Press-News.org) ANCHORAGE, Alaska — USGS streamgages show flood conditions are now underway, with live cameras providing real-time views on the USGS HIVIS website. Glacier-caused flooding has become an annual threat since 2011, with record-breaking floods over the past two years that impacted more than 300 homes and threatened public safety.

The USGS is working with the City and Borough of Juneau, Alaska Department of Transportation and Public Facilities, and the U.S. Army Corps of Engineers to monitor conditions and provide real-time data on the glacier lake releases. A glacier-dammed lake forms when a glacier blocks the natural drainage of a valley, trapping water that eventually bursts through or around the ice barrier. 

"Our real-time monitoring gives emergency managers the advance warning they need to protect Juneau residents," said Jeff Conaway of the USGS Alaska Science Center. "This information allows officials to make critical decisions about evacuations and road closures before flood waters reach dangerous levels." 
 
The USGS monitors conditions in the glacier-dammed basin using two cameras and a laser to track water and ice levels. This information is used by the NWS to forecast when and how severely flooding will occur, allowing emergency managers to anticipate dangerous conditions and make informed decisions about evacuations and road closures. 

Downstream of the glacier, the USGS streamgage on Mendenhall Lake measures water temperature and water elevation every 15 minutes. A decrease in water temperature combined with rising lake levels helps distinguish water releasing from the glacier-dammed lake from regular rainfall runoff. Working with the USACE, the USGS has installed three streamgages on downstream bridges over the Mendenhall River to measure water height and streamflow. 

Cameras installed at the bridges provide near real-time views of the river and will update to the USGS HIVIS page during the flood. USGS will measure the river bottom depth at the bridges after the flood to help officials determine if the bridges are safe for reopening. 
 
This comprehensive monitoring data helps resource managers and emergency responders protect life and property. The data can also improve flood forecasting models and assess the effectiveness of flood control measures the City and Borough of Juneau has installed along the river. 

For more than 130 years, the USGS has monitored flow in selected streams and rivers across the U.S. The information is routinely used for water supply and management, monitoring floods and droughts, bridge and road design, determination of flood risk and for many recreational activities.  

END