Stormwater Flow Controls

Urban development has caused significant changes in patterns of stormwater flow from land into receiving waters: water quantity increases have also changed water quality.    Changes in water quality can be affected when runoff carries sediment or other pollutants into streams, wetlands, lakes, and marine waters or into ground water.  The impact of altered hydrology also has increased erosion along banks and watersheds.

Flow controls are designed to:

• Control flood flows to their current levels and maintain peak flows within the capacity of the conveyance system for most storm events.
• Control the durations of geo morphically significant flows and thereby maintain existing channel and streambank erosion rates.
• Mitigate water level changes in certain volume-sensitive water bodies such as lakes, wetlands, or closed depressions where severe flooding problems have been documented.

Many states or municipalities will require flow control rates based on certain storm events. Typical storm frequencies evaluated include the two-, five-, 10-, 25-, 50-, and 100-year storms The level of flow control required is based on the resource value of the receiving system in terms of its hydrology, ecology, geology and water quality.