Glacier Outburst Flood Modeling

In collaboration with the City and Borough of Juneau, the USGS Alaska Science Center, NOAA, and University of Alaska Southeast, the AK CASC is working to create a model to forecast the timing and size of outburst flood events at a glacier-dammed lake on the Mendenhall Glacier.

Since 2011, the glacier-dammed lake at Suicide Basin has released annual flood events impacting homes and infrastructure in Mendenhall Valley, Juneau’s most heavily populated neighborhood. Using monitoring equipment such as time-lapse cameras and water level gages that provide real-time information on the status of the basin, researchers will develop an outburst flood forecasting tool to improve the ability of city managers to prepare for outburst floods, as well as provide guidance to other Alaska communities that experience glacier lake outburst floods.

Why are we doing this?

• Customized tools are needed to forecast the timing and size of outburst floods released from Suicide Basin, an ice-marginal basin on the lower Mendenhall Glacier near Juneau.
• Suicide Basin has experienced annual glacier lake outburst floods since 2011. Recent flood events have resulted in the evacuation and inundation of the Mendenhall Glacier campground, closure of several residential streets in the Mendenhall Valley, and flooding of homes along the river. High peak discharges during outburst floods exacerbate erosion problems along Mendenhall River.
• Suicide Basin has evolved rapidly given the sustained thinning of Mendenhall Glacier. Changes in ice dam height, lake extent, and ice volume in the basin have complicated forecasting efforts.
• Given the rapid changes at Suicide Basin, continuous, comprehensive monitoring of the basin is a high priority. The monitoring needs to provide sufficient data for improved flood forecasts, while remaining cost-effective.
• Improved forecasts will aid the process of initiating and implementing closures and evacuations within the Mendenhall Valley. The methods developed for Suicide Basin (both monitoring- and forecasting-wise) will also be transferable to other sites in Alaska and beyond that are subject to glacier lake outburst floods.

Approach

The monitoring plan is developed around the existing monitoring equipment in Suicide Basin, which consists of a webcam and lake level gauge maintained by the US Geological Survey. We have added climate stations and also employed drones to map the basin and create digital elevation models that contribute to our understanding of the volume of water that can be stored in and released from Suicide Basin.

The information collected from the drone imagery is particularly helpful for flood forecasting (e.g., current water level in the lake, current lake extent, and bathymetry).

Together with information derived from the analysis of previous events (e.g., typical drainage times, post-drainage water levels), we developed a statistical model that produces flood forecasts for the National Weather Service and the City and Borough of Juneau. The developed methods are documented and shared for application at other sites.

End products

• A model to forecast magnitude and timing of peak streamflow at the Mendenhall River during glacier lake outburst flood events
• A comprehensive monitoring plan for Suicide Basin that provides key data needed for flood forecasting
• An in-depth assessment of the flood events that have originated from Suicide Basin since 2011, with the goal of creating a more accurate flood forecasting model

Partners

City and Borough of Juneau, US Geological Survey, University of Alaska Southeast, NOAA National Weather Service Office and River Forecasting Center, Alaska Division of Geological & Geophysical Surveys