What is the detention time in stormwater BMPs?

The detention time in stormwater best management practices (BMPs) refers to the duration that stormwater is held within a BMP before it is released. This period is crucial for allowing sedimentation and other treatment processes to occur effectively. During detention, pollutants can settle out of the water column, and biological treatment processes can take place, improving the quality of the water being released downstream.

This concept is fundamental in stormwater management as it directly impacts the effectiveness of the BMP in reducing the quantity and quality of runoff entering larger water bodies. An inadequate detention time might not allow for sufficient pollutant removal, while excessive detention can lead to issues like stagnation and mosquito breeding.

Understanding this concept helps in designing and implementing BMPs that meet regulatory requirements and function effectively within the stormwater management system. Each BMP may have different design standards for detention time based on specific goals and site conditions, making this a crucial aspect for an inspector to monitor and evaluate.