Types and Function of Stormwater Facilities

Stormwater facilities can range from simple and small (e.g., a bio-filtration swale with mowed grass) to large and complex (e.g., ponds or underground structures with piping systems).

What they have in common is a design that collects stormwater and in some fashion filters contaminants out of it. They approach this task in one or more of the following ways:

Collecting and transporting stormwater

Runoff from large but infrequent storms can usually be collected by means of open ditches or catch basins and pipes. It’s important to keep the individual components of these systems free of weeds, debris or anything that can clog the grates, pipes or ditches. If the integrity of the system is compromised in this way, flooding and property damage can occur.

Holding and reducing water flow

Hard surfaces such as roads, roofs and parking lots aren’t able to absorb stormwater to the extent softer surfaces can. This may result in runoff into natural streams, leading to stream or channel erosion and flooding. Some detention facilities, such as ponds and underground vaults, are designed to detain and slow the flow of stormwater to surface waters. allowing for controlled release.

Storing and treating runoff

In nature, trees, vegetation and microbes help break down and remove pollutants carried by runoff. Detention basins are a way to accelerate this process on a large scale by temporarily storing or retaining runoff while it soaks into the ground. This reduces the amount of  stormwater that flows into waterways.

Multiple facility systems

In most cases, a multi-pronged approach is need to remove pollutants such as oils, chemicals, metals and sediment from stormwater runoff before it is discharged to ground or surface water. So in a given district, you may find simpler systems such as swales and wet or dry ponds working in concert with complex systems composed of underground vaults with cartridge filters or oil/water separators.