What is a Watershed?
By Sharon Campanelli
East Middle School, Auburn
and Sheila Myers, Finger Lakes Institute
What is a watershed?
The land surrounding a body of water is called its watershed. Precipitation in a watershed will either infiltrate in the ground or runoff into local streams and rivers that feed the lake. If you think of the watershed as a bowl and the lake at the center or bottom of that bowl, you can envision how any contaminants such as road salt, pet wastes, and excessive soil loss could impact and "fill-in" the bowl. There are a number of factors that influence how much rainfall will runoff and how much will infiltrate into the ground. These factors include the topography and elevation of the watershed. The steeper the watershed land area, the faster the runoff will reach the lake. The type of land cover will also affect runoff. Watershed covered in vegetation and forests provide a chance for rainfall to be absorbed by plants and filtered into the ground. Watersheds covered in hard or impervious surfaces cause the rainfall to runoff more rapidly because there is no plant material to stop and absorb the flow of water. In this lesson students will learn about how the topography of a watershed contributes to non-point source pollution.
At the end of this lesson students should be able to:
MST Standards for Intermediate
Standard 4 Key idea 7 - Human decisions have a profound impact on the environment.
Social Studies Standard
Standard 3 Key idea 1,2 - Geography
The goals of this lesson is to develop an awareness of watersheds. This lesson uses the Owasco Lake watershed as an example. The students will be using topographic maps to visualize the role that topography plays in stormwater runoff. It can be replicated for any watershed using the links below to the USGS map resources. Before undertaking the activities you will need to discuss with your students how to read a topographic map. The USGS has a lesson on this and other background information.
In Activity 1 they will also see or make a model of a watershed. Many Soil and Conservation Districts or Cornell Cooperative Extension offices have the Enviroscape Model which is a visual representation of a watershed and stormwater flow in a watershed to borrow or have some demonstrate the Enviroscape watershed model contact the county office (see references below). After the use of the Enviroscape - or in place of - the students can make their own model watershed using either clay or paper to form their landscape. Discuss with them how activities in the watershed may impact the lake or stream that receives the runoff.
In Activity 2 the student will focus their attention on the role of topography in runoff. After viewing a map of New York State they will be asked to answer a few questions. They will then view topo maps of Owasco Lake watershed (not the entire watershed). They will focus their attention on Dutch Hollow Brook, a major tributary to Owasco Lake. After examining the topo maps they will answer questions and then link to a web page (referenced below) that explains some of the runoff issues on Dutch Hollow Brook. The maps you will need for this lesson are linked below under materials except the map of New York.
Answer to Questions about Map of New York
1) Where is the highest elevation of the Finger Lakes region - in the North or South of the Lakes?
2) What major body of water do the Finger Lakes drain into?
2) What are the two major river systems that drain the Finger Lakes?
Answer to Questions on Owasco Lake
1) How many towns does Dutch Hollow Brook flow through?
2) What is the highest elevation around Dutch Hollow Brook?
3) Where does the creek end?
4) What is the major landuse in the watershed?
5) What pollutants do you think might reach Dutch Hollow Brook?
ELA extension: After researching the Dutch Hollow Brook website have the students create a brochure that explains the problems facing Dutch Hollow Brook. Students will make a presentation to the class. The teacher may want to invite a representative from the local lake association to speak to the class about the environmental issues facing the lake. See links to the Finger Lakes Institute for references.
Materials needed for activities:
For best results, maps should be printed on a plotter for correct resolution. If you print in 81/2 x 11 paper you will lose resolution. After downloading your map copy to disc and send to a printer. Laminating the maps is also a good idea for future use.
USGS now has a location on their website where you can download over 60,000 1:24,000 and 1:100,000 scale topo maps. These are PDF documents that you can view with Adobe Reader. If you have a large format plotter you could print them at full scale, if not, you can copy the file to a disc and bring to a printer or print them at full scale. If you print them on 81/2 x 11 you will lose detail. (When you arrive at their site, click the "Map Locator & Downloader" image.)
County Soil and Water Conservation Districts