By the end of today's class, you should be able to do the following:

v From last time: Describe the purpose and function of a rain barrel, and make quantitative calculations to estimate how a rain barrel is involved in the water budget of a residential property in Chicago.

v Continued from last time: Work in a team to complete today's assignment, due by the beginning of next class: collect all the information you need and make all the calculations required to answer questions on the slides with white backgrounds. You must complete this assignment by Thursday's class, but will not hand it in. The PowerPoint presentation from last class appears here.

v New this time: Use concepts of length, area, volume, and flow rate to quantify hydrologic variables.

v Solve a hydrologic problem in a sequence of logical steps, using reasonable units and dimensional analysis.

Our agenda today:

Teams get together to go over their calculations

Compare answers between teams:

How big is the property? How does the area compare to an acre?

How much of the property is in garden plots?

What is the area of the roof?

What is a typical rainfall in Chicago?

How much rain will the roof collect in a typical rainfall?

Would it fill the two barrels?

How many barrels would fill in a typical rainfall?

What depth annual precipitation do we get in Chicago?

What volume annual precipitation do we get in Chicago?

What accounts for the differences between answers? Discuss issues of precision, accuracy, error, and uncertainty.

Problem-solving: (This is an abbreviated list; see more at "Hints for Solving Quantitative Problems"!)

- List what you know about the situation ("Given").
- Write what the problem asks you to find, or what the goal is ("Find").
- Draw a sketch of the situation.
- Break the problem into smaller steps.
- Choose one part or step of the problem and write a brief heading to explain what that step is about.
- Solve that part, writing units of measurement at every step. Use "dimensional analysis" as described in your textbook!
- Put a box around the answer.
- Then move on to the other steps, writing a brief heading for each one.
- When you solve the final problem, put a box around the answer.

1) How big is the property? How does the area compared to an acre? How big is an acre (in non-technical terms)?

2) How much of the property is in garden plots? How much water would be needed to give the gardens one inch of water?

3) What is the area of the roof? How much rain will the roof collect in a typical rainfall?

4) What depth annual precipitation do we typically get in Chicago? What volume annual precipitation do we typically get in Chicago?

5) What is a "typical rainfall" in Chicago? Would it fill the two rain barrels?

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Groups that finish early should consider these questions:

- How many rain barrels would fill in a typical rainfall in Chicago?
- If the rain falls at a rate of 1 inch per hour, how long would it take to fill a rain barrel?
- How
heavy
would a full rain barrel be?

*© 2007 Laura L.
Sanders.
Last updated August 30, 2007.*