Metric measures (per centime- ter of rainfall): 1. Rooftop area in square meters x 0.01 meter (1 cm) = cubic meters


2. Cubic meters x 1,000 = volume in liters


I ask students, “Will all of


the rain that falls on the school grounds reach the river or lake?” I display the table “Per- cent Runoff for Different Land Use Cover Types” to show that the type of ground cover deter- mines how much precipitation infiltrates the ground and how much runs off. Other factors affecting runoff include the soil type and its infiltration rate; the intensity and amount of rainfall; whether the ground is frozen or saturated; whether the forest is a young, fast-grow- ing forest that uses a lot of water or a slower-growing mature forest; the slope of the terrain; and the amount of soil com- paction (high density residential lawns are quite compacted, greatly limiting infiltration). I show students aerial photos of our community taken in 1975 and in 2002, which clearly illustrate changes in land cover due to changes in land use (aerial photos may be obtained from local land manage- ment agencies or city planning offices and, in the U.S., from county offices of the USDA Natural Resources Conservation Service). Lastly, the students tackle calculating the total volume


of runoff from the school grounds in one year. We first look at an aerial photo or engineering sketch of the entire school grounds and note the different land covers: pavement/ impervious parking lots, sidewalks and rooftops; football field/lawn; small wooded area. I let students loose with measuring tapes and calculators to measure the area of each cover type (measurements could be done from aerial photos


Permeable paving made of recycled plastic enables rain water to soak into the ground naturally, rather than into the municipal drain system.


if a distance legend is avail- able). After obtaining these measurements, students calcu- late the total area of each cover type, which they multiply by the average annual rainfall and by the appropriate runoff factor (the percent of precipitation that runs off, as shown on the table “Percent Runoff for Dif- ferent Land Use Cover Types”). Finally, students convert these volumes to liters or gallons of runoff. (See chart “Calculating Runoff from School Buildings and Grounds.”) We wrap up this unit by


brainstorming ways to reduce


runoff from our school grounds, such as by planting a rain garden, installing a green roof, using impervious asphalt in the parking lot, and planting shrubs and trees. We also do storm drain stenciling on the storm drains around the school. Many students are not aware that land use changes in their communities can affect the water quality of nearby streams, rivers and lakes. After this unit, they are better able to connect changes in community appearance to ecological changes resulting from changes in land cover.


More land-use investigations


The following are other science-based ideas for measuring the ecological impacts of changing land uses:


• Measure the difference in water quality at river sites upstream and downstream of a town, shopping mall, or other land use, using benthic macroinvertebrates as bio-indicators. The EPA website is a good place to start to learn about sampling methods, identification, state monitoring programs and more: <http://www.epa.gov/ wbioindicators/html/invertebrate.html>.


Land Use


1. Agricultural 2. Commercial 3. Forest


4. Pasture/fields for livestock or wildlife 5. High density residential 6. Low density residential 7. Industrial


8. Open space/non-forested 9. Wetland


Page 12


Percent Runoff for Different Land Use Cover Types Description of Ground Cover


Row crops and crop residue cover


Buildings, sidewalks, paved parking areas Trees and shrubs Grasses, legumes


Lot size smaller than 0.2 hectare (0.5 acre)


Lot size equal to or larger than 0.2 hectare (0.5 acre) Buildings and paved parking areas Lawns, parks, golf courses Standing water, vegetated


Source: Urban Hydrology for Small Watersheds, USDA Natural Resources Conservation Service, 1986 GREEN TEACHER 83


Percent Runoff 30%


95-100% 20-30% 10-30% 80% 50%


70-90% 20-40% 5%


thingermejig, UK


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