Engineering review flags low sections on Warrenton levees, city told

Warrenton commissioners heard a technical briefing showing LiDAR-identified low spots along both Warrenton levee systems and were told further hydrology and field work is needed before design decisions. Anya Mines, an engineering geologist with the consultant, said the screening found several sections that may require embankment raises or further investigation.

"So what we did was we compared the existing ground surface elevation and the flood elevation data to evaluate freeboard," Mines told the commission, describing a color-coded screen where red areas were below the required freeboard. She flagged segments more than a foot under the target and some stretches several feet low, and she cautioned that coastal transects provided by AtkinsRealis for FEMA drove parts of the worst-case results.

The staff and consultant recommended a three-part next phase: (1) an H&H (hydraulics and hydrology) review to clarify whether coastal or riverine flood elevations apply at each reach, (2) targeted ground surveys where LiDAR shows borderline deficits, and (3) subsurface and as-built record retrieval (including U.S. Army Corps plan sheets) to confirm centerline alignment and foundation conditions. City Manager noted FEMA has offered some internal review and staff will seek that input before committing to major construction.

Commissioners pressed on timing and likely cost. Mines said smaller deficits (under about one foot) are often fixable within the existing levee footprint, while larger low spots or ambiguous drainage crossings could need more extensive work and could take years to fully address across both systems if the city pursues full accreditation. Staff said the overall program will be phased and that preliminary surveys will inform prioritization for funding and design.