Q: The Environmental Protection Agency's (EPA) proposed rules often mention and refer to various watersheds. I remember hearing a definition somewhere, maybe at a logger training session. What exactly is a watershed?
A: A watershed is an area that includes all the land and water within the confines of a drainage divide or a water area consisting in whole, or in part, of a land needing drainage or irrigation. Say What!?! Basically a watershed is an area of land that drains into a stream or lake. For example, one segment of the Sabine River or the Angelina River may drain 1600 square miles. In comparison, a small stream located on the property you are logging may drain hundreds or less acres. These small watersheds are all linked together and collectively form larger watersheds like the Trinity River watershed or the Cypress Creek Basin watershed.
While forested watersheds provide the highest quality water, harvesting activities have the potential to lead to erosion that could enter these watersheds. Best Management Practices help keep the soil in place and out of the watershed. The use of streamside management zones (SMZs) and the proper construction of ditches, so that they do not empty directly into streams, help prevent siltation into streams. You can see that it is important to use SMZs and other BMPs because by protecting the smaller watersheds from erosion and sedimentation, in turn you are protecting the larger watersheds.
A watershed, depicted above, is an area of land that drains rainfall into a stream.
The figure above depicts a watershed with its associated streams. An ephemeral stream, sometimes called a drain or swag, flows water only for a short time during and after a rain. An ephemeral stream may or may not have a well-defined channel. An intermittent stream flows water at least 30% of the year continuously, but not year-round. Intermittent streams have well-defined stream channels with bottoms scoured from the flow. A perennial stream flows year-round or about 90% of the time in a year with normal rainfall amounts. It may form pools during drought conditions.
The EPA has an excellent web page that can help you learn more about watersheds. The address for that site is www.epa.gov/surf/. Any questions or comments can be directed to me.
* This article was published in the July 2000 issue of the Texas Logger