Lewisville, TX Environmental Rules: Flood Zones (2026)

Lewisville has significant flood risk due to its proximity to Lewisville Lake Dam and the presence of multiple creek corridors including Timber Creek, Fox Branch, and Prairie Creek. FEMA-mapped Special Flood Hazard Areas (SFHAs) designated as Zone A, AE, and X (shaded) affect numerous properties throughout the city. The city administers a floodplain management ordinance that meets or exceeds FEMA National Flood Insurance Program (NFIP) minimum standards. All development in SFHAs requires a floodplain development permit from the Engineering Department at (972) 219-3590. New residential construction must have the lowest floor elevated at least one foot above the base flood elevation (BFE). Substantial improvements to existing structures (improvements exceeding 50% of the market value) must also be brought into compliance. No fill, construction, or obstruction is permitted in regulatory floodways. The city participates in the Community Rating System (CRS), which provides flood insurance premium discounts to policyholders. The Lewisville Lake Dam, operated by the U.S. Army Corps of Engineers, has a dam break inundation zone that extends downstream. Properties in the dam inundation zone should be aware of emergency evacuation procedures. Flood zone determinations are available through the Engineering Department or on the FEMA Flood Map Service Center. Elevation certificates are required for construction in SFHAs.