Efforts to Curb Pollution and Richmond Highway Development, Part 3: Bio-Mimicry

Many feel that the circumstances we are in look grim and the fact that this problem is an interstate one involving three different states and the District of Columbia with their own regulatory bureaucracies makes the problem more difficult. Some state and local governing authorities have responded with research and development that have led to a wide range of newly engineered technologies. These engineered systems are beginning to have a positive impact on the watershed through a pretreatment process for storm water runoff from impervious areas before allowing the water to reenter the watershed

 While the terms engineered technologies suggests a complicated anti-pollution device, these ideas for cleaning the water before reentering the bay are a form of bio-mimicry where engineers replicate those ecosystem components of the watershed that were once abundant as natural habitats but have been in decline for the past four centuries. These areas function in much the same manner as the original wetland forests and tidal marshes surrounding the river. These forests once functioned as mechanisms of retention with the ability to soak up water like a sponge and to hold materials, sediments and nutrients. Engineers call them bio-retention devices and they come in a variety of forms and applications. The State of Maryland has been a leader in the development of these technologies while Virginia has been lagging and playing catch-up.

The larger and most common forms are bio-retention ponds which capture and fill with storm water during a rain event and then allow the suspended sediments and particulate matter to settle out before releasing the water back into the environment to flow to a nearby creek or stream. Some of these ponds are designed as wet ponds and maintain a constant level of water and eventually have emergent and submerged aquatic plants growing in them, which in turn provides habitat for animal species. Others are dry ponds where the water is drained within a few days and the pond area dries out and is simply composed of low growing grasses and plants.

Another type of bio-retention is the rain garden. Similar to the retention pond in that storm water is directed to the facility but different in that the depression area of the garden is filled with absorbent soil and mulch and is planted with a variety of native plantings that like a lot of moisture. These devices work well during rain events that are within a normal range of precipitation and can generally hold all of the water that comes into them. The plants that live in the rain garden utilize the water for growth and transpire the water back into the atmosphere. These gardens contain overflow valves in the event that a runoff from the nearby impervious surfaces exceeds a volume greater than the retention capacity of the garden. The excess water is then directed to either a drainage swale or storm sewer flowing into a bio-retention pond.

Another system that is getting a great deal of attention are green roof technologies which are surprisingly aesthetic and very functional in trapping water during rain events of an inch or less. The plants living on the green roof are sedums a type of succulent plant that can withstand extremes in temperature as well as drought. They have a low growing habit and require little maintenance and have a long growing season of eight to nine months in our region. Like in the rain garden, the plants use the water to grow and transpire the moisture back into the atmosphere. The plants grow in a thin layer of combined soil and other media that is very absorbent. Much of the water in this thin layer evaporates back into the atmosphere. The important thing is that the roof keeps the water from becoming runoff and controls the volume that would normally drain from the roof back to the surface and down a storm sewer. By having the green roof on the building we have reintroduced a permeable surface and the roof is providing ecological services.

Individually, none of these systems alone will resolve the crisis of non-point source pollution. Most of these technologies are designed to work in conjunction with one another. Combined on a development sight with a high degree of imperviousness these technologies can perform many of the ecological services that are now missing as a consequence of the fractured habitats we have within the watershed. In doing so, they can lessen the impact of our human footprint on nature.  The next time you are out and about in your neighborhood, see if you can spot examples of engineered storm water runoff facilities. You’ll be surprised at just how common they are in newly constructed areas of the county. Unfortunately, in older areas of the county such as Richmond Highway these forms of infrastructure are less common and difficult to construct since little undeveloped land is available.

Part 4 will look at some ways that individuals can make a difference in their neighborhoods and communities to help control storm water impacts to our local streams.