The Differences Between a Detention and a Retention System

May 25, 2023

Municipalities use detention and retention systems to manage stormwater, but these systems operate in distinct ways to serve different purposes. Learn the differences between a detention and a retention system to select the right stormwater management solution for your circumstances.

Temporary vs. Long-Term Water Storage

A detention system temporarily stores stormwater runoff during heavy rain events, typically for up to 48 hours. Its primary purpose is to control the water discharge rate to prevent flooding and reduce the burden on downstream infrastructure. Detention systems are commonly used in urban areas with limited drainage capacities.

On the other hand, a retention system is designed to store water for the long term. Retention systems allow water to infiltrate the ground and replenish groundwater slowly. They are often implemented in areas where water scarcity or groundwater recharge is a concern.

Water Usage Management

Another difference between a detention and a retention system is how the managed water is used. In a detention system, excess stormwater runoff is stored temporarily in ponds or basins with controlled outlets.

A detention system is designed to gradually detain and release the water, emulating a natural flow pattern and reducing peak flows downstream. Eventually, the system discharges the water into nearby bodies of water or sewers.

In a retention system, stormwater runoff is stored within the system for an extended period. That water seeps into the ground or is harvested for beneficial reuse, such as irrigation or industrial processes. The objective is to maximize water conservation.

System Design Considerations

Engineers design detention systems to manage peak flows and prevent flooding. Each system’s capacity is determined based on factors like the catchment area from which the system draws water, rainfall intensity, and allowable discharge rate. The design ensures that the system can accommodate the expected runoff volume and release it gradually to maintain flow control.

A retention system’s design prioritizes long-term storage and infiltration of stormwater. Engineers consider factors like soil type, infiltration rates, and groundwater levels to determine each system’s capacity. These systems should maximize water storage and infiltration potential while minimizing losses due to evaporation or runoff.

The Necessity of Stormwater Management

Detention and retention systems play vital roles in protecting waterways and sewer systems from the impacts of stormwater runoff. Both techniques reduce the volume of water entering sewer systems, minimizing the risk of overflow and pollution in waterways.

Excessive water can result in sewer backups, overflows, and structural damage. When you need sewer repair and replacement in New York City, call Harris Water Main and Sewer. We will efficiently service your sewer system to improve its safety and performance.

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