Civil Engineering Professional Engineer Practice Exam 2025 - Free PE Practice Questions and Study Guide

Retention basins are designed to manage stormwater by capturing and storing excess runoff during precipitation events. They play a crucial role in flood mitigation by holding stormwater in a controlled manner until it can be slowly released into the surrounding environment or drainage systems at a rate that prevents downstream flooding.

When heavy rainfall occurs, stormwater runoff can overwhelm drainage systems, leading to flooding. Retention basins act as temporary holding areas that absorb water, thereby reducing the immediate volume of water entering waterways and helping maintain more manageable flow rates. By delaying the release of stormwater, they reduce peak flows during storms, which is essential in preventing flooding in urban and developed areas.

In contrast, options that suggest increasing the speed of water runoff, constructing barriers, or completely eliminating surface runoff do not align with the primary goal of retention basins. These systems are specifically designed to balance and control the flow of water rather than to accelerate it or eliminate runoff altogether.