Flooding rains are not uncommon in Central Texas. The region has long been known as “Flash Flood Alley” due to its hilly terrain, shallow soils, and proximity to the moisture-laden Gulf of Mexico. A foot of rainfall – a third of a typical year’s total – inundated the region in just a few hours. A 40-foot wall of water rushed downstream, scouring away everything in its path: trees, vehicles, homes, bridges, and unfortunately, people.”]
Source: https://www.csoonline.com/article/2938999/incident-response-lessons-from-a-flash-flood.html