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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.