Bioretention / Rain Garden
Figure 1 | Rain Garden - Biorention Swales
Rain gardens are small-scale bioretention systems that can be used as landscape features and small-scale stormwater management systems for single-family homes, townhouse units, and some small commercial development. These units can not only provide a landscape feature for the site and reduce the need for irrigation, but can be used to provide stormwater depression storage and treatment near the point of generation. These systems can be integrated into the stormwater management system since the components can be optimized to maximize depression storage and pretreatment of the stormwater runoff, promote evapotranspiration, and facilitate groundwater recharge. The combination of these benefits can result in a decrease in the peak flow and total volume of runoff generated by a storm event. In addition, these features can be designed to provide a significant improvement in the quality of the stormwater runoff, see Figure 1 above.
These units can also be integrated into the design of parking lots and other large paved areas, see Figure 2 below. This system provides "green areas" composed of either native vegetation or landscape materials that are suited for a significant variation in moisture and temperature.
Figure 2 | Bioretention in Parking Lot
The design is not perfect, but improvements are needed with respect to inlet structure and creating a forebay. These systems may need to provide more control for oil/grease.
Figure 3 | High Density - Bioretention System (St. Paul, Minnesota (Source)
Filter strips and swales are either elongated bioretention systems or vegetated areas that are located in transition zones. These transition zones help to reduce the rate of runoff by creating detention storage and promoting the infiltration of the stormwater. The effectiveness of this application to stormwater management is a function of the hydraulic design of the bioretention system.
Figure 4 | Graded Swales in Seattle were created using an amended soil which reduced stormwater volume by 97%. These units or systems can be developed into curbside bioretention areas.
Green roofs, also called "vegetated roof covers," "living roofs," or "eco-roofs," are thin layers of living plants that are installed on top of conventional roofs. Properly designed, they are stable, living ecosystems that replicate many of the processes found in nature. Green roofs can control stormwater runoff and erosion and reduce pollution which results in improved water quality in local streams. In addition, the systems can reduce heat loss, reduce the air condition costs, increase roof life, conserve energy, provide a sound barrier, provide habitat, and provide a unique aesthetic environment in an urban area.
Figure 5 | Vegetative Roofs
Figure 6 | Porous Pavement (Requires an underdrain)
Porous Pavement or porous paving structure may be excellent material for walkways, sidewalks, patios, along shoulders of roads and paved areas (curb and channel units), use as entrance areas to bioretention systems, driveways, and possibly as an alternative to conventional paving. The porous units could include: porous asphalt, pervious concrete, open-celled paving grids, open-graded aggregate, open-jointed paving blocks, plastic geocells, soft paving materials, and porous turf.