The effectiveness of stormwater detention is discussed in terms of quantity, water quality, and institutional constraints; and research needs are identified. The results of a study by the Urban Drainage and Flood control District in Denver, Colorado, are presented to assess the effectiveness of random on-site detention in controlling flow rates along major drainageways. The study consisted of modeling an actual 7, 85-mile 2 watershed in the Denver area under the 2-, 10-, and 100-yr rainstorm scenarios, The study suggests for the Denver region that random on-site detention has the potential of being reasonably effective in controlling the 10-and 100-yr flows along major drainageways. It also suggests that random onsite detention may not be effective in controlling frequently occurring flows such as runoff from 2-yr or smaller storms, The authors also discuss the design accuracy of stormwater systems and that institutional structure is needed to ensure the design, construction, and the continued operation of detention facilities. They conclude that such a structure is a must if detention is to be an effective part of the total stormwater management program.

The approach to drainage until the early 1970s relied on swales, curb and gutter, inlets, storm sewers, and channels to carry away flow as quickly as possible. In recent years this approach has been modified by the introduction of detention storage to hold back runoff and to release it downstream at controlled rates. The concept apparently has considerable appeal because it has been widely embraced throughout the United States, Canada, and many other countries throughout the world, Although the concept of detention storage has been widely accepted, the questions regarding its effectiveness in managing stormwater runoff persist. It is relatively easy to study the hydrologic effectiveness of individual detention sites, It is another matter to study and quantify the effectiveness of a system of detention ponds, particularly if they occur randomly as to time of construction and in their location.