Engineering: Environmental Engineering: Stormwater Runoff Solutions
Designing systems that reduce flooding, erosion, and water pollution
Engineering: Environmental Engineering: Stormwater Runoff Solutions
Designing systems that reduce flooding, erosion, and water pollution
Engineering - Grade 9-12
- 1
A school parking lot has an area of 2,400 square meters. During a storm, 3.0 centimeters of rain falls. Assuming all rain becomes runoff, calculate the runoff volume in cubic meters.
Convert centimeters to meters before multiplying by area.
The rainfall depth is 0.030 meters. The runoff volume is area times depth, so 2,400 square meters times 0.030 meters equals 72 cubic meters of runoff. - 2
Explain why a paved parking lot usually creates more stormwater runoff than a grassy field of the same size.
A paved parking lot is mostly impervious, so water cannot soak into the ground easily. A grassy field allows more infiltration and also slows water movement, which reduces runoff volume and peak flow. - 3
An engineer is choosing between a detention basin and a retention pond for a neighborhood. Describe the main difference between these two stormwater controls.
Think about whether water remains in the structure all the time.
A detention basin temporarily stores stormwater and releases it slowly after a storm. A retention pond keeps a permanent pool of water and stores additional stormwater above that pool during storms. - 4
A proposed rain garden will receive runoff from a 300 square meter roof. A design storm produces 2.5 centimeters of rain, and the runoff coefficient for the roof is 0.95. Estimate the runoff volume using V = CAd, where C is runoff coefficient, A is area, and d is rainfall depth in meters.
Use the runoff coefficient because not every drop may reach the rain garden.
The rainfall depth is 0.025 meters. The runoff volume is 0.95 times 300 square meters times 0.025 meters, which equals 7.125 cubic meters. The rain garden should be designed to handle about 7.1 cubic meters of runoff. - 5
List two pollutants commonly carried by stormwater runoff from roads and explain one possible environmental effect of each.
Stormwater from roads can carry oil and grease, which can harm aquatic organisms by coating surfaces and introducing toxic chemicals. It can also carry sediment, which can cloud water, block sunlight, and damage fish habitat. - 6
A city is considering permeable pavement for a sidewalk project. Explain how permeable pavement reduces runoff compared with traditional concrete.
Permeable pavement contains spaces or joints that allow water to pass through the surface into a stone layer and soil below. This increases infiltration and temporary storage, which reduces the amount and speed of runoff entering storm drains. - 7
A detention basin must store 180 cubic meters of stormwater. If the basin has a rectangular bottom area of 300 square meters, what average water depth is needed to store that volume?
Use volume = area times depth.
Depth equals volume divided by area. The required average depth is 180 cubic meters divided by 300 square meters, which equals 0.6 meters. - 8
A stream near a new development shows eroded banks after heavy rain. Explain how increased impervious surfaces can contribute to this erosion.
Impervious surfaces send runoff into streams faster and in larger amounts. This increases peak flow, which gives the water more energy to cut into stream banks and carry sediment downstream. - 9
Rank these surfaces from lowest to highest expected runoff for the same rainstorm: forest soil, compacted lawn, asphalt, gravel path. Explain your ranking.
Compare how easily water can soak into each surface.
A reasonable ranking from lowest to highest runoff is forest soil, gravel path, compacted lawn, and asphalt. Forest soil has high infiltration due to roots and organic matter, gravel allows some water through, compacted lawn has reduced infiltration, and asphalt is nearly impervious. - 10
A green roof is installed on a 500 square meter building. During a 4.0 centimeter rainstorm, the green roof retains 60 percent of the rainfall. How many cubic meters of runoff are prevented?
The rainfall depth is 0.040 meters. Total rainfall volume is 500 square meters times 0.040 meters, which equals 20 cubic meters. Since the roof retains 60 percent, it prevents 12 cubic meters of runoff. - 11
A neighborhood wants to reduce flooding at an intersection where storm drains overflow during intense storms. Propose two engineering solutions and explain how each would help.
One solution is to add bioswales along the street to slow runoff, filter pollutants, and increase infiltration. Another solution is to build an underground storage chamber that temporarily holds excess water and releases it slowly after the storm. - 12
Explain why engineers often design stormwater systems for a selected design storm, such as a 10-year or 100-year storm, instead of designing for every possible storm.
Engineering design usually involves tradeoffs between performance, risk, and cost.
Engineers use design storms to balance safety, cost, land use, and acceptable risk. Designing for every possible storm would be extremely expensive and may be impractical, so engineers choose a storm size based on the importance of the site and the consequences of failure. - 13
A construction site has exposed soil near a storm drain. Identify two temporary erosion and sediment control practices that should be used and explain their purpose.
A silt fence can be installed to slow runoff and trap sediment before it leaves the site. Straw mulch or erosion control blankets can cover exposed soil to reduce raindrop impact and keep soil from washing away. - 14
A proposed bioswale is 20 meters long and 2 meters wide. It can temporarily pond water to an average depth of 0.25 meters. Calculate its storage volume in cubic meters.
First find the surface area, then multiply by depth.
The bioswale area is 20 meters times 2 meters, which equals 40 square meters. The storage volume is 40 square meters times 0.25 meters, which equals 10 cubic meters. - 15
Create a brief design recommendation for a high school campus that has flooding near a parking lot, muddy runoff from a sports field, and warm runoff entering a nearby stream. Include at least three stormwater strategies and explain why they fit the problems.
A strong recommendation would include permeable pavement or a detention system near the parking lot to reduce flooding, vegetated buffer strips or erosion control improvements near the sports field to trap mud and sediment, and a rain garden or shaded bioswale to slow and cool runoff before it reaches the stream. These strategies address runoff volume, sediment pollution, and thermal pollution.