Mapping Exercise 2 (Delineating a Watershed)

This exercise deals with watersheds and contour lines.  A watershed is an area of land that drains into a lake or river.  Any precipitation that falls within that watershed will run downhill carrying sediment and other materials into the river or lake.

Above shows a 3-dimensional image of English Brook watershed.  Watersheds can be constructed on paper using contour lines.  All streams, rivers, and lakes have a unique watershed.  Some smaller watersheds make up part of larger watersheds.  For example, the Lake George watershed is part of the Lake Champlain watershed.  So anything that falls into the Lake George watershed will eventually find its way into Lake Champlain.  Subsequently there are many smaller watersheds that make up the Lake George watershed, such as English Brook above. 

In this exercise, you are going to try to delineate (trace the outline of) the Smith Brook watershed using the topographical map from exercise 1 and some hints below.

Hint1: Think of a watershed as an irregular shaped sink that surrounds the stream.  If a drop of water falls at a particular point, will it fall into the watershed or out of the watershed?  Try to find the edge of that sink.

Hint2: Contour lines that are V-shaped represent troughs or valleys and sometime contain streams or intermittent streams.  Contour lines that are U-shaped represent ridges and act as boundaries of a watershed.  Below is an example.  The red arrows point to troughs and the blue arrows point to ridges.

Now try to draw the watershed for Smith brook and its two intermittent tributaries.  The mouth of the Smith Brook is located at the red triangle.  To help get you started some of the watershed has already been started. 

Directions:

1. Locate the mouth of the stream.

2. Put small "X's" at the high points along both sides of the brook, working your way upstream towards the headwaters of the watershed. 

3. Starting at the mouth, draw a line connecting the "X's" along one side of the watercourse. This line should always cross the contours at right angles (i.e. it should be perpendicular to each contour line it crosses). It will probably also follow along the ridges (the U-shaped contours).

4. Continue the line until it passes around the head of the watershed and down the opposite side of the brook. Eventually it will connect with the outlet from which you started. At this point you have delineated the watershed of the wetland being evaluated.

Teacher: Click here to view completed map.