Welcome to the Mendenhall Glacial Lake Outburst Flooding Technical Report public information webpage. The purpose of this site is to provide information to interested parties about the U.S. Army Corps of Engineers - Alaska District's work developing a technical report of the Mendenhall Glacial Lake outburst flooding that affects Juneau citizens living in the Mendenhall Valley. 

In August 2024 and previous years, a Mendenhall Glacier outburst flooding event, known as a jökulhlaup (Yah-cuh-laup), or a glacier lake outburst flood (GLOF), occurred in the Mendenhall Valley near Juneau, the state capital, in Southeast Alaska. Present day Mendenhall GLOFs began occurring in 2011 when the retreat of Suicide Basin left an open space alongside the Mendenhall Glacier. This over-deepened bedrock basin is known as Suicide Basin. These GLOF events occur most years; however, the rapid retreat of the Suicide Glacier and changes to the Mendenhall Glacier has increased the severity and likelihood of flooding. Each year, the basin fills with rain and meltwater before bursting under the Mendenhall Glacier and downstream into the Mendenhall Lake and River. The last two years of flooding have been unprecedented with water levels at the USGS Mendenhall River stream gage peaking at 14.97 feet and 15.99 feet in 2023 and 2025, respectively. Due to the dynamic nature of the evolving glaciers and river hydraulics, geometry and evolution, two GLOF events with the same water level rise at the stream gage can lead to different rises in the river, and a given rise at the stream gage can cause a greater rise along parts of the river. These river heights flooded neighborhoods in the Mendenhall Valley creating severe risk to life and property.

The August 2024 event eclipsed all previous events with a peak discharge of 42,700 cubic feet per second (cfs). It caused widespread damage in the valley impacting about 300 residences. For context, a 2020 FEMA Flood Insurance Study lists that the 0.2 percent chance exceedance (a 500-year event) would have a discharge of 26,060 cfs at the outlet of the river. More than 300 homes were damaged in the 2024 event. 

In March 2025, the USACE National Flood Fight Materiel Center at the Rock Island District shipped ten trucks of flood fighting supplies to support flood mitigation efforts in Juneau. The supplies originated from five staging areas in four USACE divisions.

Technical reports serve to document research, engineering analyses, planning analysis, and other technical work performed by or for USACE. They are used to inform decision-making, guide future actions, and provide a record of USACE's work. ​Typically, these reports include detailed information about the project's objectives, methodology, results, conclusions and recommendations. They may also include data, calculations, models, and other technical information relevant to the project. USACE is authorized to conduct this effort under Section 8315 of the Water Resources Development Act of 2022 (WRDA).

In short, a technical report helps USACE understand the parameters of a potential project to inform larger studies related to the Federal interest and to determine the best engineering solutions.