This article is reproduced with permission of the International Technology and Engineering Educators Association (ITEEA). Learn more about comprehensive STEM programs and teacher resources at www.ITEEA.org.
Harry T. Roman
In this activity, we are going to design a water utility system, one that uses surface runoff into an open reservoir as the potable water source. There is going to be some math, so hang on!
If water will flow from that deposited by rain on the ground into a reservoir, we will first need to know how much water will run-off that ground surface and into the reservoir. Challenge your students to see how much water can be harvested from say 1 square mile of surface area. Assume 1 inch of rain falls and 90% of what does fall ends up in the reservoir. For this activity, we will assume the reservoir to be 2 square miles in size, and deep enough to hold all the water that will drain into it.
After this baseline calculation is completed, here are some of the important assumptive facts of the problem:
- The rainfall in the area where the watershed is to be located is 48 inches per year.
- Snowfall in the watershed area is about 32 inches per year.
- 10 inches of snow, when it melts, will yield about 1 inch of water run-off.
- There are 50,000 people in a local town that will use the water from this reservoir.
- Each person will use 150 gallons of water a day.
A first order of business will be to calculate how much water is consumed by the town each year. Since we already know what 1 square mile of land area will yield for each inch of rain that falls, we can figure out how many 1 square mile units of land area we will need to supply the annual water needs of the town. It is important to run these numbers out, letting the students see the value of mathematics in design; and how mathematics lends perspective to problem solving. This will allow the students to see how big the entire watershed and reservoir will be. It might be advisable to add a bit more land area to provide some extra capacity in case of droughts, emergencies, and special operating needs. Usually engineers add some incremental capacity to such calculations to take into account the vagaries of weather and customer use. Adding 15-20% to student calculations is generally a good thing to do.
Take the opportunity at this time to discuss some of the land management issues that must be considered with such a large land area in the watershed:
- How do you control pollution in the watershed?
- What needs to be done to restrict development in the watershed?
- Can the watershed be used for recreation or other duel use purposes?
- Is it advisable to allow motor boating on the reservoir?
- How would trees and plant growth be managed?
- How would it be possible maintain safety and security of such a large surface area?
- What is needed to maintain the quality of the water?
- What kinds of expertise will be needed when hiring employees to manage the watershed area?
These are not simple questions — ones that hydraulic and water engineers struggle with every day. Multi-faceted and multi-dimensional, these questions require compromise and mediation between teams of experts in many areas. And of course public commentary and interests also need to be included. These are questions that can years and even decades to resolve.
Bringing the Water to Town
We shall need to make another assumption. Our watershed is to be located in the mountains; and we can simply pipe the water downhill to the folks in town. So what now remains is to design a piping system to do just that. How big should the delivery pipes be? How many pipes should be installed? What route should the pipes take?
Students should study how water engineers have designed and constructed water delivery systems. This information can be researched in libraries, magazine articles, and of course on the Internet. This is an excellent opportunity to see engineering in action. Contact your local water company and ask if one of their engineers can come out to talk with the students. I think you will find a very receptive mood from your water company; and they will learn a great deal about how water gets cleanly and safely to each and every citizen. These engineers can also educate you and the students about how emergency and extraordinary events are handled. There are other national sources of water utility information available such as the American Water Works Association (AWWA) in Washington, DC. They have an information-filled website, with resources available for teachers to use.
This challenge provides a nice gateway to study other related aspects of the water delivery system. For instance, what role and how much can water conservation play in reducing total overall water consumption? Look at the size of the watershed the students have designed. What would happen if 10%, 15%, or maybe 25% of the water needed by the town were reduced through conservation? What other things in the water delivery system does this affect? If there is now extra capacity in the water system, what can be done with that capacity?
How do water engineers provide for operational problems that may arise in their delivery system? Do they add redundancy into their piping designs so the water in the system can be re-routed while certain sections can be shut-down for emergency or scheduled maintenance?
What might happen if there was a huge spurt in the growth of the town and this greatly increased the amount of water the town needed; and there was no longer any available land in the watershed that could be acquired? How might this increase in customer water demand be accommodated?
What technology can your water utility use to read customers’ meters? Will meter readers walk round and read everyone’s meters; or is there some electronic technology that will allow them to read meters much more cost effectively?
When thinking about how much water use rates will be for customers, try and make a list of the cost components your water utility will have to deal with. Here are just a few to get you started:
- Employee salaries and benefits
- Taxes on the watershed land
- Maintenance of the water piping and delivery system
- Chemical costs to keep water quality levels up to standards
- Reading of meters and bill processing
- Maintenance of a truck and service van fleet
- Tools and materials needed for repairs
What other cost components can you and the students identify?
By the way, how are water hydrant water use accounted for in water utility system design and operation?
Chances are that your students will never see that water faucet again the way they used to, appreciating now what it takes to get the water to where it is needed. Water is just one of the important infrastructures we depend upon every day. You can repeat this exercise for electric utilities, natural gas distribution systems, sewage systems, and also with some modifications to telephone and cable delivery systems. Have fun.