Name _______________________________________ Class _______ Date _______________
Inquiry Activity • Paper and Pencil
Chapter 14
Problem
Watershed Boundaries
How do you define the boundaries of a watershed?
Background
Why Watersheds?
Not all of the water that flows out of the mouth of a river started at its source.
Tributaries, surface runoff, and even some groundwater contribute to a river’s flow.
Along the way, this water can pick up pollutants and concentrate them in the river.
Because of this, ecologists studying river systems often want to consider pollution
sources from the entire watershed—the area of land that drains into a river system.
Water Runs Downhill
To define watershed boundaries, scientists start with the fact that water always runs
downhill. Consider a raindrop that falls on one side of a mountain. It will flow
down the side it fell on, not run up and over the mountain’s peak. Because of this,
the boundaries of a watershed are formed by high points, like mountain peaks and
ridges. A ridge is a narrow stretch of high land with a slope on either side.
Ecologists identify watershed boundaries by reading topographical maps.
Topographical maps show the elevation, or height above sea level, of landforms by
using contour lines. A contour line connects points on the land that occur at the
same elevation. Contour lines help you see the rise and fall of three-dimensional
landforms on a flat two-dimensional piece of paper. For example, the images below
show a side view, and a topographic representation of the same mountain.
Sample Topographic Map
Side View of Mapped Area
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Name _______________________________________ Class _______ Date _______________
Build Map Skills
Read a Topographical Map To mark a watershed boundary, you need to
know how to read a topographical map. Like some maps, a topographical map
looks down from above, but unlike other maps, topographical maps show the rise
and fall of the landscape. The topographical map below shows two small peaks
connected by a ridge line.
• Contour lines connect areas of the same elevation.
• Contour lines are drawn at the same interval of elevation change.
• On this map, the contour interval is 30 meters.
• In an area where contour lines bunch together, the is the change in
elevation is steep.
• At places where the contour lines spread out, the rise or drop occurs
more gradually.
1. Beside the map, draw a quick sketch of the mountain, seen from a side view.
2. What is the lowest elevation shown on the map? _______________
3. What is the highest elevation? _______________
4. Draw a line connecting the two peaks on the map, running along the highest
point of land between each.
5. Circle the area with the steepest change in elevation.
Anypeak Mountain
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Name _______________________________________ Class _______ Date _______________
Procedure
Step 1
Study the topographical map of the area around Anywater River.
Step 2
Use a pencil to locate, label, and trace Anywater River on the map.
Step 3
Find and mark with X’s all peaks or high points surrounding the river.
Step 4
Draw a continuous boundary connecting the peaks and running along
the ridges, the highest elevations that connect the peaks. To do this,
cross elevation lines at right angles. Be sure your line does not cross
the river. This boundary defines the watershed of the Anywater River.
Step 5
Lightly shade the area within your boundary line.
Step 6
Mark arrows ( > ) along the river to show the direction of the river’s
flow.
6. Use the map below to identify and mark the Anywater River Watershed.
Anywater River Watershed
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Name _______________________________________ Class _______ Date _______________
Analyze and Conclude
7. Apply Concepts Why did marking the high elevation points determine the
watershed’s edge?
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8. Explain How did you know which direction to mark the arrows to show
water flow?
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9. Draw Conclusions Why are dry land areas—not just waterways and
wetlands—included in a watershed?
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10. Infer Why is a topographical map—not just a map showing land and water
boundaries—necessary for defining a watershed boundary?
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11. Extension Why would an ecologist monitoring the water quality of the
river want to know about the types of pesticides and fertilizer used by farms
in the area?
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