Groundwater - Water We Doing to Our Planet??

Bonnie Keller
Earth Science teacher, Meadowbrook High School, Chesterfield County, VA

Question: How much runoff is created by an average shopping mall parking lot?

Objective: TSW calculate the yearly runoff created by a parking lot, and calculate the loss of water that would have entered the groundwater system.

Materials: Lab handout, pencil, calculator, paper

Background: In order for groundwater to be replenished for our use, precipitation must be absorbed by the ground. People worldwide are crying out due to lack of a stable, adequate water supply. Yet, in many industrialized countries, particularly the US, people are also demanding more construction, more roads, more shopping areas, etc. The over usage of our land is helping to cause the very water problem that used to be relegated to 3^rd world countries. This lab will illustrate how much water we lose to runoff that could have infiltrated the land and gone to the replenishment of the water supply.

Data:

Richmond, VA’s average annual rainfall is about 45”

Average ground absorption rate is 50%

An average shopping mall and surrounding parking areas is 75 acres.

1 acre = 43,560 ft ² (208.7 ft x 208.7 ft)

Calculating the amount of rain / runoff:

Square inches or cm are AREA measurements, as is an acre. But, if square inches are multiplied by another inch (or cm), the resulting unit is a CUBIC inch, which is a unit of volume, just like gallons, liters, etc. This volume unit is what we need to find. Since cubic inches do not translate into gallons, we must convert inches to cm, cm to liters, then liters to gallons.

Conversions:

1) 1 inch = 2.54 cm

2) 1 cubic inch = (2.54 cm)³

3) 1 cm³ = 1 ml

4) 1000 ml = 1 liter

5) 1 gallon = 3.8 liters

6) 1 foot = 12 inches

EXAMPLE of how to use conversion factors:

96 eggs = ?? dozen ; we know that 12 eggs = 1 dozen

96 ~~eggs~~ x 1 dozen = In this step, the “eggs” unit will cancel out, leaving the “dozen” unit

1 12 ~~eggs~~

96 dozen = 8 dozen

Now we have successfully used a conversion factor to go from one unit to another!!
NAME: ______________________________________ Date: _______________ Period: _________

Procedure:

YOU MUST FOLLOW THIS EXACTLY, OR YOU WILL NOT GET THE CORRECT ANSWER

Step one: Convert inches of rain into cm of rain

_____________ (inches per year of rain) x 2.54cm = ______________cm of rain per year

Step two: Convert acres into cm²

# acres x 43,560 ft²x (conversion #6)²x (conversion #1)² = # cm²

__________ acres x 43,560 ft²/1acre x (12 inches/1ft)²x (2.54 cm/1 inch)²= ___________________ cm²

Step three: Find the volume in cm³ and in ml

Step 1 answer x step 2 answer

___________ cm x _________ cm² = __________________________ cm³ , which is the same as ml !!!!!

Step four: Convert cm3 to liters .

Step 3 answer x conversion 3 x conversion 4 = liters

____________ cm³ x 1ml/cm³ x 1 liter/1000 ml = ________________________________ liters

Step five : Convert liters to gallons.

Step 4 answer x conversion 5 = # gallons

_______________ liters x 1 gallon/3.8 liters = _______________________ gallons

Step six: Find absorption amount.

Step 5 answer x percent absorption = # gallons lost to runoff

________ gallons x 50% absorption = ___________________________ gallons

Conclusion questions:

1) How many malls can you think of that are located in the general Richmond, VA area? ___________ Multiply this times the runoff amount and put that answer here: ___________________________

2) Now, add in other shopping centers, businesses, roads, and GUESS how many MORE gallons are lost in this area: _________________________________ (your answer may be different from other students)

3) Consider that most malls, shopping centers, office parks, etc., have empty stores or offices. What could we do to reduce the number or area of parking lots and buildings? ________________________________

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4) What else could we do to increase the amount of water absorption from rainfall?

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5) Explain why urban areas are more likely to have a water shortage than farmlands, even though farms use about the same amount of water. _______________________________________________________

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6) How would the absorption rate be different if we had a different type of soil? Be specific.

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7) What else could we do as a society to decrease the amount of land we use for building, while still not compromising the need to grow as populations increase?

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