ABSTRACT
In the 1980s, stormwater detention basins were built with a simple outlet pipe, which was designed to aim at 100-yr flow release control. In the 1990s, stormwater detention outlets were improved to have multiple layers of orifices and weirs to control 10- to 100-yr events. The latest development to the outlet works is to include a vertical perforated plate. A perforated plate can reproduce the base flow in downstream drainage systems. The drain time for a detention basin is extended from 12 to 72 hours, depending on the local water rights policies. In this chapter, the details of outwork hydraulics are illustrated with on-site construction, and are calculated with a conservative approach to ensure public safety.
