Watershed Boundaries

Background

We have all been trained to partition the world into political units. For example, we think of ourselves as residents of the Village of Millbrook in the Town of Washington in Dutchess County in New York State. Sometimes we locate ourselves with respect to major landscape features, like whether we live on the east or west side of the Hudson River. But how many of us know what watershed we live in?!

Some watersheds are very large. For example, the Continental Divide separates the United States into two enormous watersheds. Rain falling west of the Continental Divide drains into the Pacific Ocean; rain falling east of the Continental Divide drains into the Atlantic Ocean. The Hudson River watershed covers a much smaller area of roughly 13,400 square miles; water within that area drains into the Hudson River. Here in Dutchess County, an example of an intermediate-sized local watershed is the 210 square mile Wappinger Creek watershed which is itself within the Hudson River watershed -- water flows down the Wappinger Creek and into the Hudson River. The small watersheds that we are studying in the Small Watershed Ecology Assessment Project are smaller still, each encompassing less than 0.5 square mile in area.

People who live in the same watershed share a responsibility for their aquatic resources. The watershed drainage network makes it possible for pollutants to reach a waterbody that may be located many miles from the pollution source, and it means that human activities on land can impact the aquatic environment. The watershed is an important unit for resource conservation and management, yet it's a challenging concept to visualize and understand. This activity teaches students how to delineate the boundaries of a local watershed, translating the abstract concept of a watershed into something concrete and real.

Lesson

1. Give each student or group of students a copy of the topographic map that shows a small watershed. Give them a worksheet like the one titled "Drawing Watershed Boundaries" to lead them through the steps of delineating the boundaries of a small watershed.

Some of the steps outlined here for delineating a watershed are easier said than done. Bear in mind that delineating a watershed is an inexact science -- any two people, even if both are experts, will come up with slightly different boundaries. Field checking the boundaries is often helpful and it allows you to identify human alterations such as road ditches that could change the direction of water flow and affect the boundaries. One advantage to working with small watersheds is that the boundaries can be field-checked quickly on foot and through the windshield of a vehicle.