Reducing Urban Runoff (College Board AP® Environmental Science) : Study Guide

Methods to increase water infiltration

What is urban runoff?

• Urban runoff occurs when rainwater flows over impervious surfaces, such as roads and buildings, instead of infiltrating into the soil

• Excess runoff carries pollutants, sediments, and chemicals into waterways, causing water pollution

• Excess runoff also increases flood risks

  • This is because water cannot soak into the ground, causing it to accumulate quickly on surfaces

  • This overwhelms storm drains, rivers, and low-lying areas, leading to flash floods and water damage

• Reducing urban runoff helps prevent flooding, improves water quality, and supports groundwater recharge

Methods to reduce urban runoff and increase water infiltration

Permeable pavement

• Replaces traditional pavement with materials that allow water to soak into the ground

• Reduces surface runoff and stormwater drainage issues

• Examples include porous asphalt, pervious concrete, and interlocking pavers

Planting trees and vegetation

• Trees and plants absorb rainwater and slow the flow of runoff

  • Foliage intercepts rainfall, slowing the rate at which rain accumulates on impervious surfaces below

• Tree roots improve soil structure, increasing its ability to retain water

• Green spaces, rain gardens, and urban forests help filter pollutants from runoff

Increased use of public transportation

• Fewer cars on the road lead to less oil and heavy metal pollution in runoff

• Encouraging walking, biking, and public transit helps limit urban sprawl and conversion of natural land to impervious surfaces

Building up, not out

• Developing taller buildings instead of sprawling developments reduces land consumption

  • Further minimizes expansion of impervious surfaces, preserving natural landscapes

  • Allows more space for green infrastructure, parks, and wetlands, which help absorb runoff