I prematurely published this post before I was done writing and editing, so if you read it by RSS you may have gotten a rough draft originally. I apologize.
In hydrology, watersheds rule. A watershed is the entire amount of land that drains to a particular location. You can define a watershed for anything from a gutter downspout on the side of your house (300 square feet) all the way up to something the size of the Mississippi River (1,245,000 square miles, 40% of continental US).
Determining a watershed is a sticky procedure. Back in the olden days when dinosaurs smoked cigarettes and I was a new engineer it was a bit like hazing the new guy. I spent many an hour bent over contour maps tracing the high points with my pencil and then tracing them with a torturous device called a planimeter to get the actual area. Sadly, that was the waning days of doing it by hand. These days our new hires can measure drainage areas a lot more easily using digital methods.
If you’ve driven much in Tennessee you’ve probably seen the watershed signs Tennessee has on the interstates and some of the major state highways. I’ve heard a lot of questions from friends and families about them so I looked into it to see why they’re there.
Turns out the signs are a partnership between the Tennessee Department of Transportation (TDOT) and the Tennessee Department of Environment and Conservation (TDEC). They’re part of a public awareness campaign designed to make the general public more familiar with watersheds and hopefully cut down on pollution. The theory is based on the idea that you take better care of things if you think they’re yours. They announce when you enter 55 different watersheds throughout the state.
187 of the signs were installed in February and March of 2008 at a total cost of $280,194. I’ve heard a lot of debate about whether they’re worth the money. I’m not going to address that from a larger perspective, but from the TDOT point of view they’re definitely worthwhile. TDOT’s contribution was partially based on a requirement as part of an environmental permit. TDOT’s requires National Pollutant Discharge Elimination System approval in order to construct projects in Tennessee, and that permit has a requirement that a certain amount be spent on public education programs that have to do with water pollution. Participation in the sign program satisfied a lot of that.
Wikipedia has an interesting entry showing the area some of the world’s largest watersheds cover. If you’re interested in the topic you can also find out some interesting information, including looking at watershed management plans for specific Tennessee watersheds at TDEC’s watershed page. I also recommend the USGS Science in Your Watershed page.