Juneau assembly directs manager to extend HESCO flood barriers for Phase 1A after inundation maps released

The City and Borough of Juneau Assembly met May 12 in a special Committee of the Whole to review newly released inundation maps and to give immediate direction on continuing HESCO flood‑fighting barriers in the Mendenhall Valley. Assemblymembers voted, by unanimous consent, to direct the manager to move forward with a Phase 1A extension of the HESCO barriers and asked staff to return with outreach and modeling for a possible Phase 1B extension.

The maps presented to the assembly model two‑dimensional flood spread at multiple stage heights on the USGS Mendenhall Lake gauge and compare conditions with and without installed HESCO barriers. “PESCO barriers phase 1 works as intended,” the city manager said while introducing the maps. Garrett Yeager, surface water manager with Michael Baker International, the consulting firm that developed the modeling, told the assembly that the team used lidar, high‑water marks from recent events and National Weather Service hydrographs to calibrate a HEC‑RAS 2D model and that the model was validated against 2024 observations.

Why it matters: the maps are intended to inform short‑term flood‑fighting (barrier placement and emergency response) and long‑term mitigation planning. Staff said HESCO barriers substantially reduce inundation in the neighborhood east of the river at modeled stages near 16–17 feet on the Mendenhall Lake gauge; at higher stages (18–20 feet) barriers provide more limited protection and some backwatering effects may appear elsewhere.

Modeling and limitations

Garrett Yeager said the firm used a two‑dimensional HEC‑RAS model and incorporated lidar, USGS gauge data and National Weather Service hydrographs. Yeager cautioned that “all models are wrong — just some models do a better job of predicting conditions,” and stressed data limitations: lidar does not penetrate open water, channel geometry can change during floods, and the largest (19–20 foot) scenarios require discharge extrapolation beyond the existing USGS rating curve. He also invoked the engineering reminder that “garbage in, garbage out” when data are incomplete.

Staff emphasized how tides influence downstream effects and that the maps assume a high king tide worst‑case in some simulations. The presentation noted the model did not include full underground stormwater conveyance networks (only major culverts) and that smaller islands under one acre were suppressed on the printed maps for clarity.

Assembly action and next steps

Assemblymember Bryson moved that the manager be directed to proceed with Phase 1A; the motion passed by unanimous consent after a brief clarification from Assemblymember Kelly. The motion directed the manager to continue barrier installation work under Phase 1A without an additional appropriation, using equipment and budget already in place.

Staff described immediate next steps on Phase 1B: outreach to riverfront property owners, additional modeling with Michael Baker to assess downstream impacts of a longer barrier alignment, and development of funding options that could include a special tax district or other area‑wide mechanisms. The manager asked for direction on Phase 1A only at the meeting and said Phase 1B would return to the assembly with more information.

Budget and equity considerations

Staff told the assembly the HESCO project is currently under budget by roughly $2 million. Per materials included in the packet, staff said the project can be charged to the previously authorized LID (local improvement district) for HESCO barrier costs and that the LID is currently being assessed for about 40% of those project costs. Staff reported remaining appropriations that can fund Phase 1A and initial work on Phase 1B: approximately $500,000 remaining for Phase 1A and approximately $1.3 million identified for Phase 1B, according to the city memo presented at the meeting.

Managers and several assemblymembers flagged an equity question: Phase 1B would require barriers to be placed on or across private property and could protect parcels that did not participate in prior assessments. Staff said they would explore capital improvement by consent, special tax or other area‑wide mechanisms to avoid double assessment and to spread costs in a way the assembly could find fair.

Public information and tools

Deputy Manager Barr and staff said the city will publish an interactive web tool (built with University of Alaska Southeast as a partner) later in the month to let the public view multiple stage maps, toggle HESCO barriers on and off and query approximate depths at points on the map. Staff also referenced existing National Weather Service pages for Suicide Basin and the USGS gauge, and encouraged residents to sign up for CVJ alerts and the city’s flood response resources at floodresponse.juneau.org.

Taken together, staff described Phase 1A as an immediate, funded continuation of the barrier work already in place and Phase 1B as a more complex policy and funding decision that will require additional modeling and outreach before the assembly considers direction or authorization.