Google Earth Watershed Activity
Watersheds or drainage basins are comprised of a network of stream channels that link from
smaller to larger, providing conduits for surface water runoff and sediment transport on
Earth's surface. Drainage basins are defined by topographic contour patterns with drainage
divides (bounding ridges) and stream channels (defined by "V-shaped contour lines"). When
defining watershed boundaries and stream channels, it is important to remember that water flows
from high elevation to low elevation.
The example map below shows an illustration of contour lines, topography, stream channel
network, and drainage divide. The following are the steps used to delineate watershed boundaries
and stream networks:
To draw a watershed divide or boundary:
1. First examine the contour pattern, look for "contour
crenulations" or V-shape contour lines that
indicate the location of a stream valley (Below A’s).
2. Start at the "mouth" or the outlet (B in the map) of the
watershed and draw a line that follows
the highest elevation hill or ridgeline (A’s on the map).
3. Draw lines in the center of the contour crenulations to show
the drainage network.
4. Mark all the saddles (where the dots are) on the ridgelines.
Trace the outline of the watershed beginning at outlet (B) by
connecting the marks on the saddles. Be sure to cross each
contour at right angles and try to form a closed and
continuous boundary.
Create watershed
boundaries of streams
(dashed lines) on the
topographic map
below:
Google Earth Questions Regarding Surface Water and Drainage Basins
Open the .KMZ file “Google
Earth Maui watershed.”
Click on the white triangle
next to the file name
“watersheds of Maui” to
expand the contents of the
folder.
Click on “Na Wai Eha” to get
a map of the “Four
Streams.”
Click on the box next to
Maui Contours to view
contours (contour intervals
are 200 ft) of Maui.
Double click on any of the watersheds (Waikapu, Waihee, Iao, or Waiehu) to fly to their locations and to
answer the following questions:
1- Which watershed has the greatest amount of topographic change (relief)? Which has the least?
2- How might topography affect the amount of water discharged into the rivers and streams? How
might it affect the amount of infiltration of water into the soil? (hint: think of steepness and its role
in the water’s velocity)
3- Where is the final discharge point for the surface water (streams) for all four basins? Describe three
ways water in a watershed can get transported.
4- Follow the Waikapu stream from its watershed to the open flat areas. What is the surface water
being used for in this area?