Steve Nabor, city engineer, and Patrick Bean, clean water administrator, briefed council members on the Des Moines levee alterations program and a risk-informed path to FEMA accreditation.

Nabor said the levee system includes earth embankments, flood walls, closure structures, pump stations and operation-and-maintenance responsibilities. He noted the city’s levees are hydraulically linked with Corps of Engineers levees and that updated flow-frequency studies after major floods required the city to plan alterations and submit documentation to FEMA for accreditation.

Patrick Bean explained the city used a semi-quantitative risk assessment (SQRA) process, described in a 2021 Corps circular, to evaluate 41 potential failure modes (overtopping, scour, seepage, closures, interior drainage and others). The SQRA approach ranks failure modes and allows a risk-informed design that targets the primary drivers of failure rather than raising the entire levee system to a prescriptive height everywhere.

Bean said SQRA identified five primary risk drivers and showed the most critical work for the city lies in phases D and E (the segment near Southeast 14th–15th and around the wastewater-treatment plant headworks). By addressing those targeted needs—improving closures, raising limited segments and installing cutoff or seepage relief features—staff estimate the overall program cost could fall from earlier estimates near $100 million to about $66 million.

Nabor and Bean described construction already completed downtown (pump stations, scour protection, flood walls and embankment raises) and cited the Principal Park closure upgrade and new stop-log closure that reduce deployment time. Bean said additional geotechnical issues (boulders encountered while driving sheet piles) produced a change order on a floodgate project to install grout injection and stabilize piles.

Staff recommended authorizing an extension to the Corps design assessment to complete SQRA and advance design for phases D and E; they anticipate permitting and bidding then construction—with the earliest construction starts in 2027 and a target accreditation/completion window around 2029. Bean said the SQRA process both reduces scope where appropriate and builds resilience by focusing resources where failure risk is highest.

Council members asked questions about timing, trail impacts and past flood events; staff said some areas of recently resurfaced trail likely will not be impacted and that construction timing will be coordinated to minimize rework.