These lessons were developed by the Bainbridge island Woodward Middle School 6th grade team in cooperation with the Bainbridge Island Watershed Watch program.
Storm water or runoff is defined as rainfall that falls on impervious surfaces (pavement, rooftops, street, and some lawns) and is routed to natural or artificial drainage systems. Water is not the only element that is entering storm drains. Along its way, water picks up pollutants such as grease, oil, metals, bacteria, garbage and sediment. These pollutants are harmful to animals and decrease the overall quality of water. Besides adding pollutants into our waters, storm water can be harmful just by the quantity and rate in which it enters a stream. Surges or pulses of storm water can occur after a heavy rainfall. Large volumes of stormwater running off many impervious surfaces can race through drainage systems and can overflow into sewer systems, thereby combining the two systems. When this happens, raw sewage can be directly routed to the larger body of water.
The rate at which the storm water enters a stream can have dramatic effects on the stream ecology. Some drainage systems have retention ponds that slow down the flow of stormwater and allow retention ponds that slow down the flow of stormwater and allow sediment to settle out. If retention ponds fail by releasing too much water too quckly, erosion of stream beds and banks can occur.
Stormwater Field Trip
Start this school site field trip by asking students where rain water would go if the school wasn’t there. Ask them where the water is going, now that the school is located on the ground where the rain would have soaked in or would have run off into a stream, wetland or lake. As you lead students outside, have them focus on the path of a rain drop that has landed on the school’s roof. Have students look for the storm drains on the school property and in the parking lot. If possible, follow the path of the stormwater after it enteres the parking lot storm drain. Depending on the site the storm water might connect with a sewer, a retention pond or the water might enter a stream or lake directly.
Math Extension: Calculation of surface water runoff on school site.
This activity is designed to use a unique method of measurement to determine the area of all the impervious surfaces on the school property. Students will be able to calculate the amount of water that becomes stormwater in gallons and in pounds.
This exercise an be modified to calculate only the parking lot or the school roof. Student groups of four or five is suggested.
School site maps, poster board, scales.
1. Obtain large school site maps from principal or city planners.
2. Outline all the impervious surfaces and trace them onto heavy poster board.
3. cut out all impervious surfaces.
4. From a separate piece of poster cut out a 2.5’ x 2.5’ square. This square represents 100’x100’. (The size of this square should correlate to the scale of your map).
5. What is the weight of your 2.5’x2.5’ square?
6. What is the weight of your total runoff area?
7. Since the square represents 10,000 square feet and its weight is known and you know the weight of all the impervious surfaces, you can set up two equivalent fractions.
These fractions are ratios. Example: If your square weighs .55g and your impervious surface piece weighs 20.32g, then:
10,000 sq.ft— X sq. ft
Cross multiply to solve for X.
8. What is the total square footage of all the school’s impervious surface?
9. One cubic foot = 7.5 gallons. Since a cubic foot is 12” high, how many gallons of water fill a square foot area after 1” of rain? (Hint: 1/12 of 7.5 gallons).
10. Calculate the number of gallons of water that will run off all the school impervious surfaces after one inch of rain.
11. One cubic foot of water (7.5 gallons) weighs 62.5 pounds. How much would ____ (answer #10) weigh?
Language Arts Extension
Imagine you are the architect r planner that designed the school’s storm water drainage system. Students and teachers at the school need a guide that explains how the system works. Your job is to create a pamphlet that details where the water goes.
Students may work in groups. Each group must produce a pamphlet that is one complete page double sided.
Each pamphlet should contain the following:
1. A title.
2. A map of the school and the storm water drainage system.
3. An explanation, including location of storm drains, at least two erosion controls, two manholes, the retention pond, the pond’s overflow, and the outfall into the stream. (Teachers will need to modify this for their school site).4. A glossary section where the following terms are defined: non-point pollution, storm drain, runoff, storm water, sedimentation, silt, retention pond.
5. The names of the authors.