Stormwater Retention Basin Optimization Through Multi-Stage Flow Control

By Jeremy Langburt, Gianfranco Maragno, and John Cigana

Taking advantage of government regulations on stormwater effluent rates is difficult to accomplish efficiently when there are different allowable release rates for discrete storm intensities. Managing the flow for a range of events with one control device is not always possible or efficient, yet several municipalities will require flow regulation for 5-, 10-, 25- and 100-year storm events. How can one system be able to properly manage flows from storm events with a 5-year frequency and also be able to manage the 100-year storm flow?

Conventional Design Approach

A single static flow regulator used to throttle the outlet of a retention basin will meet a single design point for a specific storm frequency. However, it will typically release less than the maximum flow permitted in a more intense storm. This approach is inefficient as it retains extra water and thus forces designers to unnecessarily oversize the basin and increase its emptying time.

To meet multiple set points, a flow regulator must have moving parts. Adding mobility to a flow regulator increases the capital and maintenance costs associated with the flow control system. Additionally, using electricity to operate the moving parts increases the chances of system failure since electricity may not be available during an intense rain storm.