How can a city be built so that rainwater soaks in and stays clean instead of flooding the streets?
Topic 5.13 Methods to Reduce Urban Runoff: describe methods such as permeable pavement, rain gardens, green roofs and retention ponds that reduce urban stormwater runoff.
A focused answer to APES Topic 5.13, covering methods to reduce urban stormwater runoff (permeable pavement, rain gardens, green roofs, retention ponds, planting trees), how each restores infiltration and filters pollutants, and their benefits, with a worked runoff-reduction calculation.
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What this topic is asking
The College Board (Topic 5.13) wants you to describe methods that reduce urban stormwater runoff, permeable pavement, rain gardens, green roofs, retention ponds and planting, and explain how each restores infiltration and filters pollutants.
Why urban runoff is a problem
The methods
How they help
These practices, often called green infrastructure or low-impact development, reduce flooding (less and slower runoff), recharge groundwater (more infiltration), and improve water quality (filtering out pollutants and sediment). They also provide co-benefits such as cooling and habitat.
Why this matters
Reducing urban runoff is the practical solution to the urbanization problems of Topic 5.10, and it protects watersheds (Topic 4.6) and water quality (a link to Unit 8 non-point-source pollution). It is a clear example of designing land use to work sustainably (Topic 5.12) with the water cycle rather than against it.
Try this
Q1. Identify one method that reduces urban runoff by letting water soak into the ground. [1 point]
- Cue. Permeable pavement (also acceptable: rain gardens, green roofs, planting trees).
Q2. Explain how a rain garden improves the quality of stormwater. [2 points]
- Cue. A rain garden collects runoff in a planted depression where the soil and plants slow the water and let it infiltrate, trapping and filtering out sediment and pollutants before they reach waterways.
Exam-style practice questions
Practice questions written in the style of College Board exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AP 2021 (style)4 marksSection II (FRQ). A city suffers frequent flooding and polluted runoff after storms. (a) Explain why urban areas produce so much stormwater runoff. (b) Describe how permeable pavement reduces runoff. (c) Describe how a rain garden improves stormwater quality. (d) Identify one additional method to reduce urban runoff.Show worked answer →
A 4-point FRQ on reducing urban runoff.
(a) Explain (1 point): impervious surfaces (roads, roofs, car parks) block infiltration, so almost all rain becomes fast surface runoff instead of soaking into the ground.
(b) Describe (1 point): permeable pavement has gaps or porous material that let water pass through into the ground below, restoring infiltration and reducing surface runoff.
(c) Describe (1 point): a rain garden is a planted, shallow depression that collects runoff; the soil and plants slow the water, let it infiltrate, and filter out pollutants and sediment.
(d) Identify (1 point): a method such as green roofs, retention/detention ponds, planting trees, rain barrels, or buffer/vegetated strips.
Markers reward blocked infiltration for runoff, water passing through for permeable pavement, infiltration and filtering for rain gardens, and a valid additional method.
AP 2018 (style)1 marksSection I (multiple choice). Which method most directly reduces urban stormwater runoff by allowing water to soak into the ground? (A) Paving with standard asphalt (B) Installing permeable pavement (C) Building taller storm drains (D) Channelising streams with concrete. Justify your choice.Show worked answer →
A 1-point MCQ on urban runoff. The answer is (B).
Permeable pavement lets rainwater pass through into the soil below, restoring infiltration and reducing runoff. Standard asphalt (A) and concrete channelisation (D) block infiltration and increase runoff; taller storm drains (C) move runoff faster but do not reduce it. The trap is choosing a drainage option; the goal is to increase infiltration, not just move water faster.
Related dot points
- Topic 5.10 Urbanization: explain the environmental effects of urbanization, including impervious surfaces, runoff, the urban heat island, sprawl and saltwater intrusion.
A focused answer to APES Topic 5.10, covering urbanization, impervious surfaces and increased runoff, the urban heat island effect, urban sprawl, depletion and saltwater intrusion, and the benefits of smart growth, with a worked impervious-surface calculation.
- Topic 4.6 Watersheds: define a watershed, describe the factors that affect its characteristics, and explain how land use changes runoff and water quality.
A focused answer to APES Topic 4.6, covering the definition of a watershed, divides, the factors that shape watershed behavior (area, slope, vegetation, soil), runoff versus infiltration, and how land use affects flooding and water quality, with a worked runoff comparison.
- Topic 5.12 Introduction to Sustainability: define sustainability and sustainable yield, and explain the indicators used to assess whether resource use is sustainable.
A focused answer to APES Topic 5.12, covering sustainability, sustainable yield, the difference between renewable and non-renewable resources, indicators of sustainability (biodiversity, soil, water, productivity), and the link to natural capital, with a worked sustainable-yield calculation.
- Topic 5.9 Impacts of Mining: compare surface and subsurface mining and explain their environmental consequences, including acid mine drainage and tailings.
A focused answer to APES Topic 5.9, covering surface mining (strip, open-pit, mountaintop removal) and subsurface mining, their environmental consequences, acid mine drainage, tailings, habitat destruction, and reclamation, with a worked overburden calculation.
- Topic 1.7 The Hydrologic (Water) Cycle: describe the processes of the water cycle and explain how human activities alter the storage and movement of water.
A focused answer to APES Topic 1.7, covering evaporation, transpiration, condensation, precipitation, runoff, infiltration and groundwater, and how deforestation, paving and irrigation alter the cycle, with a worked water-budget calculation.
Sources & how we know this
- AP Environmental Science Course and Exam Description — College Board (2020)