Download Getting to Know Your Stream`s Drainage Basin

Getting to Know Your Stream’s Drainage Basin
The Activity
Part I: Using maps to identify land uses
1. Working with your group, find you stream and its watershed on the topo, street,
and aerial maps.
2. Trace the stream from one of the maps, using a solid line, on a piece of graph
paper. Trace the boundaries of its watershed on the paper using a dashed line.
Also, write or trace the scale from the map you’re tracing onto your map. Trace
any important landmarks in the basin, such as roads or buildings. Mark which
direction is north. This will be you land-use map.
3. Use the maps to identify land uses in the watershed, and label these (including
approximate boundaries) on your land use map. Be as specific as you can. Land
uses might include residential (high density or low density?), agricultural (what
type?), commercial (offices, shops, mall?), industry (what type?), recreational
(walking trails, playing fields), construction, or undeveloped (vacant lots, forested
areas, wildlife preserve?).
4. Brainstorm with your group members how the different land uses might affect the
stream, wither in positive or negative ways.
Part II: Calculate Impervious Surface in the Drainage Basin
1. Impervious surfaces are areas where rain cannot soak into the ground, such as
areas covered with pavement or buildings. First, make note of which areas on
your land-use map are clearly all impervious surface (100%) or clearly no
impervious surface (0%). Many areas will be a mix. For those areas, you will
have to estimate. For example, in a residential neighborhood, estimate what
percentage of the land is covered by houses, streets, sidewalks, and driveways.
Label each area on your map with the appropriate percentage.
2. Use the scale to figure out the appropriate area of one graph paper square. Count
the number of squares in each land-use area that has any impervious surface,
estimating where you have partial squares. Multiply the area times the percentage
of impervious surface for that land use. Remember to place your decimal
properly when doing so. For example, to figure 90% of the number multiply the
number by 0.90.
3. Based on what you have learned so far, identify any possible sources of water
pollution – either point or non-point sources. Point sources might include a
discharge pipe from an industrial plant or sewage treatment plant. Non-point
sources might include run-off from agricultural areas or from a residential
neighborhood with fertilized lawns and oily streets.
4. Based on what you have learned about land uses and impervious surface in the
drainage basin, choose some places in the stream that you and your group
members think are especially important to monitor. For example, if the stream
passes through areas with high percentages of impervious surface, you might want
to monitor in that area. Or if you’re interested to see whether a tributary is
bringing in pollutants, consider monitoring just upstream and just downstream
from where the tributary joins your stream.
Part III: Verify in the Field and Monitoring
1. Spend some time in the field verifying the land uses, particularly for the area
where the maps gave incomplete or contradictory information.
2. Monitor water quality in the areas you and your classmates identified as
important, using the testing parameters you used in Module 3 (Monitoring Water
Quality in Your Stream).
Analysis
How does knowledge of land use in the drainage basin add to you understanding of the
study stream? Describe ways the stream might be different if there were different land
uses in its drainage basin. Explain why and how land use in any stream’s drainage basin
has an affect on that stream.