Leander begins stormwater master plan; consultants identify 77 flood-risk areas, will develop projects for top 45

Leander city staff and consultant Edge Engineering on Thursday told the City Council they have completed comprehensive data collection and local storm‑drain modeling as part of a stormwater master plan and have identified 77 areas of potential flood risk across the city.

The consultants said their next steps are to prioritize those areas and develop detailed project solutions and cost estimates for the top 15 sites, plus limited design and cost estimates for an additional 30 sites (a total of 45 areas of interest). The plan is intended to feed prioritized stormwater projects into the city’s capital improvement program and a final report is expected for council adoption by the end of the year.

City Engineer Emily Truman introduced Chad Cormack of Edge Engineering, who outlined the plan’s objectives: assemble a comprehensive digital storm‑drain GIS, gather public input, model flood risk at the neighborhood level, rank and prioritize problem areas, then develop solutions and cost estimates that can be included in the CIP.

Truman and Cormack said the work builds on multiple prior studies and datasets: Williamson and Travis County creek studies, the city’s 2022 Brushy Creek study and older FEMA mapping work (the 1997 FEMA flood insurance study and subsequent updates). They are using detailed “lidar” elevation data and as‑built plans from recent developments to improve local drainage modeling upstream of creeks and inside neighborhoods.

Cormack said the team’s modeling and public input produced 77 grouped areas where models or citizen reports indicate homes or roadways could be exposed to flooding or overtopping. The consultant described a three‑part ranking system for prioritization: up to 40 points for properties at risk, up to 35 points for roadway infrastructure risk, and up to 25 points for documented citizen‑reported or historical flooding. After solutions are developed for the top 45, additional scoring will include cost effectiveness, maintenance requirements, project impact, potential overlap with other projects (roads or utilities), outside partner coordination and external funding opportunities.

Council members asked about the scope of the lidar elevation data, how the plan will address future development and impervious cover, and whether the plan will inform updates to the city’s drainage policy. Cormack and Truman said the elevation data represents the ground surface (it does not model subsurface features) and that the master plan will identify existing flood inundation and green‑space footprints to help prevent new development from making existing problems worse. Truman noted the city currently requires detention for new development and said the drainage‑policy review in the study could recommend further refinements.

Truman said public outreach has been a large component of the project: an open house last fall in this room, presence at the Old Town Festival, a project website, social posts and a web survey with an interactive map and photo uploads so residents can flag historic flood locations. The consultants said that those citizen reports were incorporated into the prioritization process.

Planned deliverables: detailed project development (including cost sheets) for the top 15 areas of interest; limited‑detail project descriptions and cost estimates for the next 30; a ranked list of stormwater projects; a final stormwater master plan document that council can formally adopt and integrate into the CIP.

Council members expressed support for the approach and asked staff to return with the completed project cut sheets and prioritization for formal adoption and integration into the capital program.