Schoolyard Stormwater Runoff: An Audit and Design Project

The situation. Every time it rains, water hits the schoolyard's roofs, sidewalks, parking lots, and fields. Some of that water soaks into the ground. The rest does not soak in. It flows across the surface instead. Water that flows like this is called runoff. It runs across pavement, into gutters, down downspouts, and into storm drains. Then it leaves campus completely. It usually heads for a creek, river, or storm sewer. The school may never have studied where that water actually goes. Where does the school's rainwater go? Your team's task is to find out.

Your task. Your team is a stormwater audit crew. An audit is a careful check of something. Stormwater is rain that runs off instead of soaking into the ground. Over five sessions, you will map your schoolyard's hard and soft surfaces. You will estimate their area by pacing off distances. You will calculate how many gallons of runoff a single one-inch storm produces. You will trace the path that water follows once it leaves each surface. Finally, you will design one real improvement: a rain garden, a rain barrel, or a redirected downspout. Any of these could capture or slow some of that runoff. Your final deliverable is a pitch. You will write a real letter to your principal or facilities manager. You will also give a short spoken pitch. Both will present your improvement with evidence behind it.

The math you will use. Water professionals use one formula for this. It turns a hard surface's area and how much rain falls into a number of gallons.

Area (square feet) × rainfall (inches) × 0.623 = gallons of runoff

Here is a worked example. It uses a made-up roof, not your school's real roof. You will measure your own school's roof later, in Milestone 2. Picture a school gym roof that measures 2,000 square feet. This size is only for practice. Now imagine a storm that drops 1 inch of rain:

2,000 sq ft × 1 in × 0.623 = 1,246 gallons

That one made-up roof produces a lot of water. In a single storm, it makes more water than a typical American household uses in four days. The average household uses about 300 gallons of water each day. All of that runoff can leave the roof within an hour or two. Your job is to find out what your own school's surfaces produce, and where that water goes next.

Your audience is real. The letter your team sends in Milestone 5 goes to a real adult. This person can act on what your team finds. Write and speak like you expect to be taken seriously.

1. Surface map — Session 1 (50 minutes). Walk your assigned part of the schoolyard. Stay with your group and an adult, and keep out of driving lanes in parking lots. Bring a clipboard and the site-map handout. If you are drawing freehand from an aerial photo, bring a blank sheet instead. Sketch a bird's-eye view of every surface you cross. Include roofs, sidewalks, parking lots, and the blacktop. Also include play structures with rubber surfacing, grass fields, mulched garden beds, and bare dirt. For each surface, decide whether it is impervious or pervious. Impervious means hard: water runs off instead of soaking in, like pavement, rooftops, and rubber play surfacing. Pervious means soft: water soaks in, like grass, mulch, and bare soil. Label each surface with one of these two words. Draw an arrow on any slope to show which way the ground tilts. Do not worry about exact scale yet. Today, your job is to find every surface and label it correctly. Exact measurements can wait until next session.
   Deliverable: A hand-drawn site map. Your team should pick one consistent scale and use it throughout. Every surface must be labeled hard or soft. Add slope arrows wherever the ground is not flat.

2. Area estimates and runoff math — Session 2 (50 minutes). Return to each hard surface on your map. Estimate its area. Pace off the length and width of each rectangle. If a surface is an irregular shape, break it into rectangles and triangles. Use a known pace length or a tape measure to check your steps. Multiply length by width to find the area of each rectangle in square feet. For a triangle, find half of base times height. Then use the class formula: area times rainfall in inches times 0.623 equals gallons. Use a 1-inch storm for every surface. Add up every hard surface's gallons. This gives your team's total estimated runoff from a single 1-inch storm. Show your area math and your runoff math for each surface. A bare number with no work will not earn full credit on the rubric.
   Deliverable: A table listing every hard surface. For each surface, show its estimated area in square feet. Also show its calculated runoff in gallons for a 1-inch storm. Include a team total at the bottom.

3. Drain hunt and flow tracing — Session 3 (60 minutes). Walk the site again. This time, follow the water instead of mapping surfaces. Follow the same safety rules as in Session 1, and do not lift grates or reach into drains. Find every storm drain, grate, ditch, downspout outlet, and low spot where water collects or flows after rain. A downspout is the pipe that carries water down from a roof's gutter. Ask custodial or facilities staff where they have seen standing water. They usually know before anyone else. On your map, draw arrows to trace water's path. Show the path from each hard surface to the nearest drain or outlet. Mark where each drain seems to lead. It might lead to a storm sewer, a ditch, or a creek. Sometimes your team cannot tell without asking someone. Your town or school district may publish a stormwater map or a watershed map. A watershed map shows all the land that drains into the same river or lake. If your district has one, use it to check your guesses about where the water ends up.
   Deliverable: A flow map with labels. It should show drain and outlet locations, plus arrows tracing water's path from at least three hard surfaces. Add a one-paragraph explanation of where your schoolyard's runoff appears to end up.

4. Design proposal — Session 4 (45 minutes). Choose one location on your map where your evidence shows runoff is a real problem. It might be a flooding low spot or a drain that cannot keep up. Or it might be a large hard surface with no capture at all. Design one improvement for that location. You can choose a rain garden, a rain barrel, or a redirected downspout. A rain garden is a planted, shallow dip in the ground that catches runoff and slowly soaks it up. A rain barrel is a container that catches roof runoff from a downspout. The water it collects can be used later. A redirected downspout means moving where roof water comes out. That way, it soaks into a better spot instead of running onto pavement. Sketch your design in place on the map. Name your design's criteria. Criteria are the goals your design must meet. One criterion is how much runoff it should capture or slow. Another is where the water needs to end up instead. Also name your design's constraints. Constraints are the limits your design must work within. These include the space you have, a realistic budget, and who would maintain it. Finally, build a simple cost-benefit comparison. This means comparing two things: what the improvement would cost to build, and the benefit it delivers in gallons captured or slowed. Base your numbers on your Milestone 2 and Milestone 3 math. Your Milestone 2 gallons are all the rain that falls on a surface, so a real barrel or rain garden will catch somewhat less than that.
   Deliverable: A one-page design proposal. Include a labeled sketch and a plain-language description of how the improvement works. State your criteria and constraints. Add a cost-benefit comparison in a simple two-column list or table.

5. Pitch to a real audience — Session 5 (45 minutes). Write a professional letter to your principal or facilities manager. In it, present your team's findings and your proposal. Explain what you measured, how much runoff a 1-inch storm produces, and where that water currently goes. Recommend your improvement, and include your cost-benefit case. Then prepare a two- to three-minute spoken pitch. Deliver it using your map and design sketch as visual support. Speak to convince your audience, not only to report facts to them. Name the specific problem your evidence found. Make a specific ask: tell the decision-maker exactly what you want them to consider or approve.
   Deliverable: A signed, mailable letter addressed to a real school decision-maker. Also, a short rehearsed oral pitch delivered to the class. If your teacher can arrange it, deliver the pitch to the real audience instead.