Bioswales are landscape elements designed to remove silt and pollution from surface runoff water. They typically consist of a swaled drainage course with gently sloped sides (less than six percent) and filled with vegetation, compost and/or riprap. The Bioswales in the downtown area are connected to curbed parking area that direct the flow to a bioswale inlet. The water’s flow path, into the landscaped area in the sidewalk, is designed to maximize the time water spends in the swale, which aids the trapping of pollutants and silt. Depending upon the geometry of land available, a bioswale may have a meandering or almost straight channel alignment. Biological factors also contribute to the breakdown of certain pollutants.
The bioswales are attached to parking areas, where substantial automotive pollution is collected on the pavement and then flushed by rain. The bioswales have inlet within the cub of the parking area and treats the runoff before releasing it to the storm sewer and ultimately to the stream.
The bioswales serves to treat several types of pollutants including silt, inorganic contaminants, organic chemicals and pathogens. In the case of silt, these effects are resultant turbidity to receiving waters. Inorganic compounds may be metallic compounds such as lead, chromium, cadmium and other heavy metals. Lead is the most prevalent chemical of this class, deriving from automotive residue (e.g. surface spillage of leaded gasoline). Other common inorganic compounds are macronutrients such as phosphates and nitrates. Principal sources of these nutrients are excess fertilization, which can cause eutrophication in receiving waters. Chief organic chemicals are pesticides, frequently over-dosed in agricultural and urban landscaping. These chemicals can lead to a variety of organism poisoning and aquatic ecosystem disturbance. Pathogens typically derive from surface runoff containing animal wastes and can lead to a variety of diseases in humans and aquatic organisms.