The Town of Flower Mound lies within the Denton and Elm Fork Trinity Watersheds. The Denton Watershed drains to Lake Grapevine and the Elm Fork Trinity Watershed drains to Lake Lewisville. The flood hazard areas in Flower Mound are mainly, but not limited to, locations along the creeks named Bakers Branch, Graham Branch, McKamy Creek, Sharps Branch, Timber Creek, Whites Branch, Wichita Chase, Wichita Creek, their tributaries and the low lying areas surrounding Lake Grapevine. These areas are subject to flash flooding, flooding from sustained rainfall, and/or Lake Grapevine flood control operations by the United States Corp of Engineers (USACE).
These areas have been identified on FEMA’s Flood Insurance Rate Maps (FIRM’s) as the Special Flood Hazard Area (SFHA). The SFHA is the area predicted to flood during the 1% annual chance storm event. The SFHA is based on conditions at the time the FIRM’s were produced. Over time conditions change due to watershed development. As the watershed develops the amount of rainfall runoff increases.
Therefore, the Town requires new development to analyze and predict the extent of flooding when the watershed is fully developed. The Town prohibits development of these areas. This provides a level of protection to structures from current predicted flooding and future flooding events.