Flooding & Floodplains

HARRIS COUNTY'S WATERSHEDS

A web of watersheds and sub-watersheds

A watershed is a land area that ultimately drains rainfall runoff (or stormwater) to a common body of water. In the United States, for example, the huge Mississippi River watershed includes the smaller but still mighty sub-watersheds of the Ohio and Missouri rivers, part of a drainage web that stretches from the Pacific to the Atlantic, as well as to the Gulf of Mexico. Smaller bayous, creeks and gullies branching off of larger “main stem” waterways are said to have their own sub-watersheds as well.

Zooming in shows that most of Harris County is in the San Jacinto River watershed. Within that larger area, most Harris County watersheds drain into one of nearly two dozen major creeks and bayous. For example, if you live in the Brays Bayou watershed, the rain that falls on your house will eventually end up in Brays Bayou.

 

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Harris County has classified 22 major watersheds that each drain into 22 major waterways. The watersheds come in all shapes and sizes. Some are large, some small... and each has its own independent flooding issues.  

Watershed boundaries are formed by nature and are largely determined by the topography or "lay of the land." Through study, we're able to locate and map those boundaries, which sometimes cross city or county borders.

As part of its mission, the Harris County Flood Control District has identified 22 major watersheds that drain into one of our major waterways. Each one is associated in Flood Control District records and reports with a different letter of the alphabet. Buffalo Bayou and its tributaries, for example, are associated with the letter “W.”

Little Cypress Creek, often referred to as “Harris County’s 22nd watershed, is a significant exception, since it is actually a tributary in the larger Cypress Creek watershed. While it is not always delineated separately on watershed maps, Little Cypress Creek does have its own watershed letter, “L.”

Another notable Harris County subwatershed is Halls Bayou, which is a major tributary of Greens Bayou, designated by the letter “P.” While Halls shares the “P” watershed letter with Greens, it is the sole focus of the ongoing Halls Ahead planning effort.

Watersheds in Harris County come in all shapes and sizes – some larger, some smaller. Each eventually drains into Galveston Bay… and each has its own independent flooding issues.