San Antonio releases Kleinfelder analysis of June 12 Bridal Creek flood; city outlines steps to reduce future risk

The San Antonio City Council heard an independent analysis on Nov. 6 of the June 12 Bridal Creek flood that swept vehicles off the westbound Loop 410 frontage road and resulted in multiple fatalities. Justin Murray of Kleinfelder, Inc. told the council the event was "consistent with a 25 year storm event" and that dense vegetation just north of the frontage road caused prior models to underpredict water-surface elevations at the Loop 410 sag point.

The analysis and city response matter because the hydraulic modeling validated by more than 300 high-water marks showed rapid inundation and high velocities on the frontage road during the pre-dawn hours. City staff said they will act on the report’s recommendations to reduce the probability of a repeat and to improve public safety and operational response.

Justin Murray, a Kleinfelder consultant, summarized the firm’s scope and findings: a combined integrated hydrology-and-hydraulics (H&H) model for the roughly 13-square-mile Bridal Creek watershed, a detailed hydraulic model for the area around Loop 410, bridge structural reviews and geotechnical channel assessments. Murray said the team collected high-resolution lidar, bridge surveys, bathymetry and about 303 high-water marks to validate model results.

Kleinfelder found the rainfall on June 12 matched a 25-year event (roughly a 4 percent chance in any year) with a peak…