What Is a Watershed?

What is a Watershed?

Overland flow moves only a short distance over the ground before it gathers into minute threads of water. These threads merge with one another, forming rivulets capable of eroding soil and shaping a small channel. This system of channels is called a drainage network, and it represents nature’s most effective means of getting water off the lands. The area feeding water into the drainage network is the drainage basin, or watershed.

Modern land development often alters drainage networks by altering natural channels, and man-made channels, or by changing the size of drainage basins. Deforestation, agriculture, and land development may initiate soil erosion, gully formation, and expansion of the drainage network. Discharges are in turn larger, higher flows occur with more frequency, erosion is greater, and water quality can be expected to decline.