Updated August 2021
Stormwater — the runoff from rainfall, melting snow, or ice — sounds harmless enough. But, left unchecked, stormwater can contribute to costly flooding and pollution issues that wreak havoc on our communities.
Since we can’t control the weather, implementing stormwater best management practices (BMPs) is one of the most effective ways to avoid the consequences of excessive runoff. BMPs can help you:
- Reduce stormwater runoff — and associated ramifications including erosion, flooded basements, and backed-up sewers — on your property.
- Meet National Pollutant Discharge Elimination System (NPDES) permit requirements.
- Supplement your stormwater pollution prevention plan (SWPPP).
Here are four examples of BMPs that can help you control stormwater runoff.
Dry detention basins
Also called dry ponds, dry detention basins are a BMP used primarily for controlling water quantity versus quality, as they only confine stormwater for a short amount of time.
Here’s how they work:
- During and immediately following storm events, the basin fills with stormwater runoff.
- Particles and pollutants settle to the bottom. (Note: Water rarely remains in dry detention basins for longer than 24 hours, but the longer the water stays in the basin, the more the water quality improves.)
- When the water reaches a certain level, an outlet designed to throttle flow rate drives water into nearby streams or storm sewer systems, leaving the dry pond empty.
Dry ponds also employ emergency spillways that guide water away from the basin during major storm events. Both the outlet and the emergency spillway must be designed and maintained to eliminate the risk of erosion.
Dry detention basins are one of the most commonly applied stormwater BMPs, as they don’t require any specific climate conditions to be successful.
In addition to managing stormwater runoff, dry detention basins function extraordinarily well as a flood control measure. And, as previously mentioned, they can be applied in almost every climate with only minor design alterations.
The primary limitation of dry detention basins is available construction space — dry ponds require a good chunk of impervious land area. If the land area is too small, the outlet system may prove ineffective due to clogging when storm events occur.
Although widely applicable as a stormwater runoff BMP and flood control measure, dry basins are not recommended as a sole solution in “stormwater hot spots” or areas where runoff is potentially highly contaminated.
Retention basins are artificial lakes or ponds that treat stormwater runoff by emulating the water treatment capabilities of natural watersheds. Runoff that collects in the basin undergoes natural treatment processes:
- Sedimentation promotes the removal of particles, organic matter, and metals.
- Biological uptake from plants, algae, and bacteria works to remove pollutants further.
Retention basins maintain a constant level of water, only releasing to receiving water after significant storm events. This is one of the main differences between dry ponds and retention basins.
Retention basins are a good solution for almost any application with sufficient land. They can also replace existing detention basins. Retention basins are most suitable for areas with highly permeable soil, as this allows water to pass through more quickly to decrease the water levels.
In addition to functioning as a stormwater control measure, these artificial ponds:
- Significantly improve water quality.
- Recharge groundwater.
- Add aesthetic appeal to communities.
- Stay functional for more than 20 years with proper maintenance.
Much like the dry ponds, retention basins are not appropriate for every location. They come with a hefty upfront cost and a few important considerations:
- During the initial design and construction phase, it’s crucial to look for potential disturbances to the surrounding wetland areas and/or groundwater contamination. Any major design flaws can result in decreased water quality.
- It will also be necessary to conduct periodic inspections of surrounding vegetation after construction, as well as regular evaluations of the structure itself.
Vegetated or grassed swales are shallow, open channels tasked specifically with slowing stormwater runoff while also removing pollutants. The sides and bottoms of the channel are lush with vegetation, as you may have guessed from the name.
These swales are suitable in any area that can support dense patches of vegetation. They function exceptionally well in residential and industrial areas that don’t stay overly wet and maintain a lower water flow.
Vegetated swales can be a sole solution or combined with other BMPs. They also encourage infiltration of water and slow water flow.
Considering the design aspects of swales, they are not as successful in extremely flat or steep graded areas. They are also unable to withstand high water flow. And, with no protection below the swale, pollutants may reach groundwater.
Anything stored outside and exposed to rain and/or runoff should have a covering if it has the potential to contaminate stormwater. Coverings include anything temporary, like a plastic covering or tarp, or something more permanent such as a roof or building enclosure.
Coverings are a widely applied BMP, as many facilities have raw materials, byproducts, and other final products that could pollute stormwater runoff.
Coverings are exceptionally easy to implement in a myriad of situations and, in many cases, prove to be pleasantly cost-effective.
They require frequent inspections, and some types of coverings may not be as effective as originally intended.
Selecting the right BMPs
When choosing which BMPs to include in a stormwater solution, consider these questions:
- What are the climate and weather conditions of the area?
- How much land is available, and is it suitable for construction? Look into factors like topography, soil type, and proximity to other bodies of water or drainage areas.
- How much maintenance will be required to keep the BMP operating effectively?
- How will the BMP impact the aesthetics of the property and/or community?
- What effect will the BMP have on the surrounding environment (e.g., water quality, fish and wildlife, insect control, odor, etc.)?
There is no one-size-fits-all solution for managing stormwater runoff at your facility, so it’s worth considering several different solutions before implementing one. These five general descriptions of stormwater BMPs are only a few of countless ways to keep your stormwater runoff under control.
- Stormwater Pollution and Prevention Plan (SWPPP) development
- Spill Prevention, Control, and Countermeasure (SPCC) plan development
- Stormwater testing, monitoring, and reporting