Biofiltration & Water Damage

If designed properly, a biofiltration retention pond (or a biofiltration swale) negates the effects of water damage. Without it, storm runoff and other runoff water damage can occur because of rain-path erosion, silt sedimentation in rivers and streams, and debris buildup. Furthermore, water damage can occur if pollutants leach into the subsurface water table, making the water undrinkable. A number of concerns are involved when designing a biofiltration pond, such as location, topographical layout, cubic feet of storage and wall lining. Mississippi State University and the State of Washington present several key points in the design criteria, and these should be relied upon when designing a biofiltration pond or swale.

Background

• Storm runoff is not clean water but rather is full of sediments, pollutants and litter that is carried along. Because water always seeks the lowest level, a funnel effect occurs within the surrounding topography, and debris funnels into a depression. For example, if a farmer just sprayed pesticides, the rain runoff from the field accumulates and concentrates the pesticide runoff into that depression. Also, storm runoff tends to form streams (again following the topography). If left alone, these streams eventually widen, and the current flow erodes all the topsoil. Not dealing effectively with soil erosion was one of the contributing factors of the Great Dust Bowl of the 1930s because many thousands of riverlets carried away many thousands of cubic feet of topsoil.

Purpose

• The purpose of a biofiltration pond or swale is to deal with water and water pollution damage effectively in an eco-friendly manner. Because nature has the effect of accumulating and concentrating, all the sediments and pollutants have to be contained and dealt with. Also, because soil erosion can cause significant damage over time, conservation practices are in place to direct runoff into predetermined channels, which then flow into the pond.

Design and Placement

• A well-designed biofiltration swale is key.

  The design and placement of a biofiltration pond is usually done by civil engineers, environmental engineers or geologists. First, they analyze the surrounding topography. Then they test the percolation rates of the underlying strata (commonly called a "perc test") of where the pond will be placed. Based upon the perc test, they calculate the size of the pond. Much research has been done in this area.

Environmental Concerns

• The goal of a biofiltration is to deal with water damage in a least harmful manner to the environment. It is designed to have runoff absorb slowly into the underlying strata and to provide catch basins for sediment. Another concern is to direct the runoff flow into predetermined channels to stop soil erosion. Still another major concern is how to stop pollutants from leaching into the groundwater, contaminating the water table. Modern methods use aquatic plants in ponds and swales to biofiltrate the pollutants, thereby lessening the environmental damage.

Conclusions and Recommendations

• The conclusions drawn by many years of research indicate that a biofiltration pond or swale is an effective, low-cost, eco-friendly method of dealing with water damage. For a farmer or large land owner, having retention ponds strategically placed is an excellent way to deal with runoff and soil erosion. For a municipality, having biofiltratioon swales is also an excellent way to deal with large-scale runoff from storm drainage systems. Before a pond is placed, a geologist or bioengineer can be consulted to design the most efficient system for the project's needs.