Stormwater management facilities are required pursuant to the Delaware Code. The State of Delaware adopted regulations in the early 1990s that require land developers to control the quantity of stormwater runoff for land development projects to the pre-development flow rates for specific storm events. The same regulations also contain requirements that are intended to manage the pollutant levels in stormwater runoff. The enforcement of these regulations has been delegated to New Castle County since July of 1991.
There are different types of stormwater management practices. The type that is implemented depends on site specific conditions including the compatibility with the type of development, location in a drainage watershed, and existing land conditions. The following stormwater management practices are typical in New Castle County.
Wet ponds should contain a permanent pool of water that is a minimum of 3-feet deep. Their outlet structure is above the surface of the water, so the pond should stay full most of the time. Stormwater only discharges from the pond when the water level rises over the outlet as a result of runoff from a rainstorm.
A surface area with a runoff storage area that is normally dry during dry weather conditions, but stores stormwater as it rains. Such a detention facility does not have a permanent pool of water and the entire volume of the runoff storage area is utilized to store stormwater runoff.
Typically broad, grass covered ditches with a relatively flat grade. These are constructed where stormwater flow rate control is not necessary. These provide filtering and infiltration of stormwater runoff back into the ground.