What is a watershed?
A watershed is the geographic boundary of a creek, river or stream – it’s the area of land from which water drains to a particular water body. Watersheds come in all shapes and sizes, and there are watersheds for every body of water, whether it is the creek flowing through your neighborhood or the Mississippi River. No matter where you are, you are in a watershed. A river basin consists of all the watersheds that flow to that river.
Think of a funnel. Everything that falls into it, flows together, concentrates and flows from a single point into a receiving body or stream. Just as gas flows through a funnel to your lawnmower, water flows from the land within the watershed, to the creek, down the creek and into the receiving stream.
The Upper San Jacinto River Basin above Lake Houston contains 13 major watersheds. But, there are many smaller watersheds within each larger one. Notice how the watershed boundaries begin at a place where one stream flows into another stream or water body.
There are only three ways for water to get from one watershed to another. It can flow directly into it, man can pipe from one to another, or the water volume can become so great that it causes the water to rise high enough and overflow into the neighboring watershed.