A detention basin is an excavated area installed on or adjacent to development, to store water during precipitation events. These basins are also called “dry ponds,” “holding ponds” or “dry detention basins” if no permanent pool of water exists.
Detention basins that are designed to permanently retain some volume of water at all times are called retention basins. In its basic form, a detention basin is used to manage water quantity while having a limited effectiveness in protecting water quality, unless it includes a permanent pool feature. Often these basins are vegetated with basically lawn grass; mowed regularly and offering little or no wildlife habitat.
Opportunities to restore, enhance and improve detention basins exist that still provide for the intended function and design of the detention basin, but also dramatically improve wildlife and pollinator value of the detention basin. Restoration and enhancement would benefit a variety of wildlife including grassland nesting birds, neotropical birds, local reptiles, amphibians as well as pollinating insects.
To restore habitat in detention basins, the following prescription can be used. If the basin is wet (but not flooded) most of the year, plant the basin floor with a wetland herbaceous mix (e.g., sedges, rushes, bulrush). If the basin floor is flooded, then either leave unplanted or add submerged aquatic plants along the edges. If the basin floor is dry most of the year, plant warm season grass and wild flowers. Native grass seed for the project can include switchgrass (Panicum virgatum), big bluestem (Andropogon gerardi), little bluestem (Andropogon scoparius), and Indiangrass (Sorghastrum nutans). Wildflower species can also be planted, including black-eyed susan (Rudbeckia hirta), lance leaved coreopsis (Tradescantia ohiensis), and butterfly milkweed (Asclepias syricia). Side slopes surrounding the detention basin can similarly be planted with native warm season grasses and/or wildflowers.
Once established, the native grass stand should be mowed at least once every three to four years to prevent woody vegetation from establishing. Such a mowing schedule will significantly minimize routine mowing (which is often multiple times a year). Maintenance mowing should not occur between April 15 and July 15 of any year to prevent disturbance to grassland-nesting birds and to pollinators.
Additionally, the top edge of detention basins can be planted with low height shrubs to further enhance the detention basin. Woody vegetation above the detention basin will not affect functioning or design of the basin. Additional enhancements can be added to the project depending on interest and visibility of the site including nest boxes to encourage cavity-nesting bird nesting in the area (e.g., bluebirds (Sialia sialis)), and interpretive signs.
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