Nature

Why the Hill Country is A.K.A. ‘Flash Flood Alley’

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Though beautiful to live in and visit in the best weather (and still gorgeous in less-than-stellar weather conditions), according the National Weather Service, the Texas Hill Country is the most flash flood-prone region in the country and has fast become known as “Flash Flood Alley”.

A Conduit

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Photo: mysanantonio.com

Leading the United States in the number of flash and river flooding-related deaths annually (an ominous honor), Texas, specifically the Hill Country, is the most flash flood-prone region found in North America. With its breathtaking views, gorgeous rivers, and rugged landscapes, its beauty is a beacon but also a conduit for danger in excessive rains. Flash flooding occurs when rainfalls in the amount of 8-15 inches fall in a few hours, causing rivers to rise 11-15 feet in some cases.

The Balcones Escarpment Effect

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Photo: nsf-margins.org

Part of what make the temperate climate, and enjoyable eco-system of the Hill Country is also its bane. The Balcones Escarpment consists of a series of cliffs dropping from the Edwards Plateau to the Balcones Fault Line. This outer rim of the Hill Country (if you will) with its limestone providing a stark contrast to the rolling hills, is the formation point for many large thunderstorms, which then stall along the uplift and then hover over the Hill Country.

Rainy Season(s)

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Photo: chron.com

With 2 rainy seasons (April/May in the spring from thunderstorms, and September/October in the fall resulting from tropical storms in the Gulf of Mexico) Texas has to deal like a sponge – soak up what it can and eventually hope to dry out. In the spring however, with an excess of rainfall in comparison to tropical storm season, “Flash Flood Alley” worsens due to the ground becoming saturated and the water having nowhere else to go.

A Funnel Effect

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Photo: theprestemons.wordpress.com

To highlight this fact, note that rain water flows down from the hills into the creeks, streams and rivers we all enjoy as a part of the Hill Country, however the narrow and sometimes sheer valleys it runs through can help to form a type of surge that would otherwise not be present in a lesser grade. Subsequently, what may be considered a shallow creek bed can quickly become 10-ft. deep within an hour.

Runoff Literally Has Nowhere to Run Off

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Photo: jasonrweingart.com

Ground saturation, coupled with the rocky terrain of the Hill Country aggravates developments in “Flash Flood Alley”. With less soil comes less soaking of rain and run off, leading to almost imminent flash flood development.