During the week of August 11, the Mendenhall Glacier released its yearly glacier lake outburst flood, also known as a jökulhlaup (Yah-cuh-laup). In preparation for the potential threat to infrastructure and public safety, the U.S. Army Corps of Engineers provided temporary flood mitigation barriers to the City and Borough of Juneau last winter. While USACE continues to prepare a technical study that will help to define the parameters of an enduring flood risk mitigation solution, these barriers provided vital short-term protection to the community along the river this week by holding back the glacial water released from Suicide Basin and performing well during the peak of the floodwaters.
“As we continue to evaluate the performance of the barriers, I’m confident they prevented a lot of property damage compared to 2024,” said Brig. Gen. Joseph “Clete” Goetz, commanding general of the U.S. Corps of Engineers - Pacific Ocean Division.
Originating from the USACE National Flood Fight Materiel Center in Illinois, about 37,800 linear feet of barrier wall; 400 supersacks; 112,000 sandbags and 25,000 linear feet of polyethylene sheeting were shipped to Juneau during the winter and spring of 2025 and strategically installed along the Mendenhall River by the City and Borough of Juneau in two phases. Phase one was completed in spring 2025 and covered about 2.5 miles between Marion Drive and Rivercourt Way. Phase two will build upon lessons learned at this year’s event and provide coverage to the remainder of the area.
As the lead federal agency for floods, USACE provided technical assistance and advisement to the community through the process. Installation of these materials is a challenging process that takes the flood event data of the previous year into consideration. This information can include high-water marks, topography and ground conditions. Depending on the high-water marks, the height of the barriers varies in each location. The decision was made to build to the high-water elevation with an additional four feet. In some cases, this resulted in a barrier two units high, or eight feet above the natural ground.
“The successful deployment of these temporary flood protection barriers is reflective of a total team effort with our stakeholder, tribal and community partners,” said Col. Jeffrey Palazzini, commander of the U.S. Army Corps of Engineers – Alaska District. “The preparation and partnership were on full display during the flood event of the past 24-48 hours.”
As of Aug. 14, the barriers have performed well in response to record high floodwaters in the Mendenhall River Valley during the week. However, further assessment is still needed to determine the full extent of any damage.
The last two years of flooding have been unprecedented with water levels at the U.S. Geological Survey (USGS) Mendenhall River streamgage peaking at 14.97 feet and 15.99 feet in 2023 and 2024, respectively. This week, the river reached a record high, with the largest flow measuring 16.6 feet.
Furthermore, USACE leadership has been fully engaged on site during the event, seizing the opportunity to closely monitor the capabilities of the barriers in real time and meet with stakeholders and community members. Although an enduring solution will take years to fully develop, short-term flood mitigation efforts in Juneau continue to be a high priority at all levels of the organization.