General Design Standards for Bio-swales

Swales are water conveyance systems that are designed into the grading plan to move water to points of collection or disposal. Swales must be designed with high points, low points, center lines, bottom slope and side slopes. Swales must be designed for specific depths and lengths. Bio-swales shall not exceed on and one half percent (11/2) percent slope to allow for slow percolation, infiltration and transpiration by native wetland plants. Colonies of wetland plants that spread by underground tuber, rhizomes, roots, or bulb division should be introduced at the upstream location of the swales. These bio0swales my also occur within the boundaries of slotted curbs within parking lots to capture pollutants run off from parked cars. Planting design criteria for bio-swales require that (30) percent of the swales be planted. A minimum of seven (7)species of plants shall be included in the design with at least two of those species being evergreen during the winter months. The design should utilized Class C trees, small shrubs and perennial ground cover and flowering plants.

Bio-swales within parking areas of twenty-five (25) cars or more and wide and shallow grassed swales or outflow pipe may be used to link them to outfall points. Pipe size for cross transfer should be sized as six (6) to eight (8) inch pipe.

 

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