Date: Sun, 23 Mar 2014 13:01:26 EDT
Summary: Flow in the North Fork Stillaguamish River, WA, has been partially blocked since a deadly landslide occurred Saturday morning; flooding may occur upstream due to ponding behind the natural dam and downstream when the natural dam is breached.
A large landslide occurred in northwest Washington at about 11 AM PDT on Saturday morning (March 22) that partially blocked flow in the North Fork Stillaguamish River. Flooding may occur upstream due to ponding behind the natural dam and downstream when the natural dam is breached. The breach could happen any time. Emergency responders have evacuated affected areas.
The National Weather Service (NWS) has issued a flood warning but considers catastrophic flooding unlikely. For the NWS flood warning, see http://forecast.weather.gov/wwamap/wwatxtget.php?cwa=usa&wwa=flood%20warning.
Three people are confirmed dead as a result of the landslide; at least another 10 people are missing. See news story at http://www.cnn.com/2014/03/23/us/washington-landslide/index.html?hpt=hp_c2.
The USGS operates a streamgage (North Fork Stillaguamish River at Arlington, station no. 12167000) about 12 miles downstream from the landslide. For near-real-time gage data, see http://waterdata.usgs.gov/wa/nwis/uv/?site_no=12167000. The river level at the gage dropped suddenly at about 1:30 PM PDT on Saturday. Based on current (9:15 AM PDT) measurements, the drop in water level has been about 1.2 feet, which is equivalent to a drop in discharge of about 1,200 cubic feet per second. USGS staff continues to monitor the gage remotely.
Graphs showing drops in gage height and discharge, North Fork Stillaguamish River at Arlington, station no. 12167000