Objectives

1. Students will map and calculate the area of the school parking lot.
2. Students will calculate the volume of water falling on the school parking lot.
3. Students will map the route surface runoff will take to the nearest water body.
4. Students will describe the roles that human activity and runoff play in urban nonpoint source pollution.

 

Materials

• Meter or yardstick
• Tape measure
• Trundle or measuring wheel (optional)
• Long piece of twine or rope (marked in meter or foot increments)
• Magnetic compasses
• Writing materials
• Clipboard
• Graph paper or computer graphing program
• Protractors
• Rulers
• Calculators
• Local rainfall data

 

Background

 

Procedure

1. Explain to students that they are going to examine the impacts of runoff from the school parking lot.
2. Review reading a magnetic compass:
• Hold the compass level in front of you where no metal object (e.g., a belt buckle) will interfere. Point the direction-of-travel arrow (located on the base plate of the compass) facing away from you toward a landmark or reference point.
• Next, twist the compass housing (the circular dial) until the compass needle (the red moving arrow) lies in the orienting arrow (outline of arrow on circular dial). Note: Make sure the north part of the compass needle points toward the letter N (north) on top of the compass housing.
• Read the number on the compass housing where the direction of travel arrow touches the compass housing. This is the bearing expressed in compass degrees.
3. Have students estimate the size of the parking lot and the expected runoff. You may choose to use only a portion of the parking lot due to its size. Have students write down these estimates and the annual amount of runoff.
4. Write several estimates on the board, including the lowest, highest and your own estimate. Which estimate does the class think is the most accurate? They will compare these estimates with their final answers.
5. Divide the class into three- to five-member teams. One team member will be required to sketch the site and record measurements. Another member will need to operate the compass. Other team members will need to make site observations and take distance measurements.
6. Instruct teams on how and in what units to make their measurements. NOTE: Use either standard or metric measurements, but do not mix measuring units.
7. Distribute compass and measuring equipment to each team. Note: Students can determine the distances by using a piece of rope or twine marked with appropriate increments, by determining a team member’s length of stride (how many paces does it take for the student to walk 100 feet [ft] or meters [m]) and pacing off the distances, or by using a measuring wheel.
8. Have the teams make rough sketches of the parking lot on plain paper. The measurements taken will be recorded on this sketch for later use.
9. To make sketches, include or do the following:
• Choose a central reference point such as a flagpole or other landmark that will not change over time. Their map will be drawn in relation to this point. Note: Use only one reference point.
• Begin sketch by locating the landmark selected in the center of the paper. Then use the compass to note N, S, E, and W.
• Locate all prominent features and other relevant information on the sketch.
• For example, determine the course of the runoff and the distance to an aquatic habitat, if appropriate. Where does the water go from the parking lot? What route does it take? What is the nature of the route? What is the groundcover? Is it below or above the ground? Have students put arrows on their maps to show the direction of stormwater flow.
• Instruct them to record any evidence of potential nonpoint sources of pollutants (type and approximate location.)
• Identify points around the edge of the parking lot that they can use later as reference points when they take their measurements. Permanent features like doors, windows, trees, or signs work well. Have them clearly mark these points on the sketch.
10. Next, have the teams determine the dimensions of the parking lot. Since many parking lots are not perfect rectangles, they will need to map the approximate shape of the parking lot by using a magnetic compass to detect directional changes.
• Have the team member with the compass stand next to the central or reference point. The recorder should be standing next to him/her with a copy of the sketch.
• The magnetic compass is used to determine angles (in compass degrees) between measurements. To use the compass, point it at one of the permanent features you previously selected and placed on the sketch. Take a compass reading and have recorder write this on the sketch next to that point.
• Measure the distance from the central point to this feature and record on the sketch.
• Repeat this procedure by choosing another point and taking a new compass reading and measurement. Use this information to make a more accurate map on graph paper later.

Note: An alternative to using this method would be to use a survey instrument or GPS (global positioning system) unit to develop a topographic map with locations.

11. Prior to graphing the site map, students need to determine the map scale. From the largest dimension, the students will need to decide upon an appropriate map scale to use and which direction on the paper will be north. For instance, what will the side of one square equal? What will a square represent? For example, the vertical side of one square might equal 2 ft and the horizontal side might equal the same or it could be different, like 4 ft. Use whichever scale will work best for the site (be consistent) and will keep your map on one sheet of paper.
12. Redraw the parking lot to scale on graph paper using a protractor and a ruler, or use a computer graphing program. Note: If the teams all measured the same site, the maps should look the same even if they choose to use different points for their central landmark and permanent features.
• Place the central reference point in the center of the graph paper. Note: Be sure this point is located where two lines bisect.
• Use a protractor to mark the compass degrees from the reference point. Use the measurements on the rough sketch and the map scale chosen to determine the number of squares away from the central point each measurement should be. Mark the point.
• Connect the appropriate dots.
13. Calculate the area of the school parking lot. Note: The formula is AREA = LENGTH x WIDTH.
• Determine what area each square on the graph paper will represent using the map scale selected. For example, if the vertical side were 2 ft or m and the horizontal scale 2 ft or m, the area would be 4 square feet (ft2) or square meters (m2).
• Count and record the number of squares completely within the boundaries of the parking lot on your map.
• Then count the squares only partially within the boundaries, divide this number by two, and add to the number of complete squares.
• Multiply the total number of squares by the conversion factor determined by the map scale used. Record this information on a piece of paper.

Conversion Formula: # of complete squares + (# of partial squares/2) = total # of squares. From map scale, 1 square = Y ft2 (or m2); let Y = your choice of map scale; thus, the total # of squares x Y ft2 = area of parking lot in ft2 or m2.

14. Have students calculate the average annual amount of rain falling on the parking lot. Local rainfall data can be obtained from a variety of sources and agencies.
15. Have students determine the annual volume of rain falling on the parking lot. To calculate, have students multiply the average rainfall by the area of the parking lot. Volume should be recorded on their data charts in cubic feet (ft3) or cubic meters (m3), as these are the standard units for runoff used by professionals. A cubic foot of water is enough water to fill a square box measuring one foot on each side or about 6 gallons.
16. Have students convert the volume into gallons or liters, and determine how many showers they could take with this amount of water. Since a paved parking lot will not absorb any water, the volume of rainfall approximately equals the volume of runoff. Note: Some water will evaporate when rain falls on hot pavement. Have students calculate and record on their data chart the number of 5-minute showers to which the annual amount of rainfall and runoff from the parking lot is equal. Finally, if you took one shower each day, how long would it take to use the amount of water from the runoff?
17. Have students use the following conversions to calculate the weight of the runoff:
    1 ft3 = 7.2827; 1 m3 = 1,000 liters; 5-minute shower = 25 gallons or 95 liters
    Density of water: 1 gallon = 8.34 lbs; 1 liter = 1 kilogram

Example Problem Using Standard Units:

Average annual rainfall is 100 inches (in.), and the area of the parking lot is 12,000 ft².

Convert the rainfall from inches to feet (12 in. = 1 ft):
100 in. (annual rainfall)/12 in. = 8.33 ft

Multiply the rainfall by the parking lot area to find the volume of runoff:
8.33 ft (annual rainfall) x 12,000 ft2 (area) - 99,960 ft3 (annual runoff)

Now, convert the volume of gallons (1 ft3 = 7.2827 gallons):
53,978 ft3 x 7.2827 gallons/ft3 = 727,979 gallons runoff

Next, determine how many 5-minute showers could be taken with this amount of water:
7,27,979 gallons (annual runoff)/25 gallons/5-minute showers = 29,119 showers

If you took one shower every day, how long would it take to shower this many times?
29,119 showers x 1 shower/1 day x 1 year/365.25 days = 79.72 years worth of showers

Determine the weight of runoff: 727,979 gallons x 8.34 lbs/gallons - 6,071,334 lbs

18. Discuss the following:

• Comparison of student estimates to the information calculated.
• How does runoff relate to nonpoint source pollution?
• Review the types of pollutants that may enter a water body from a parking lot.
• What kinds of pollutants did the students observe when they took their measurements?
• What could be done to reduce nonpoint source pollution from their school parking lot?

 

Extensions

 

Sunshine State Standards