Best management practice fact sheet 15: Extended detention ponds

Extended detention ponds (EDs) are dry detention ponds that provide 12 to 24 hours of runoff storage during peak runoff events. Releases from the ED ponds are controlled by an outlet structure. During a storm event, as the discharge restriction is reached, water backs up into the ED pond. The pool slows flow velocities and enables particulate pollutants to settle. Peak flows are also reduced.