If stormwater were to be considered a valuable resource, on the same level as metals, paper, and even plastics, one could apply many of the same principles of Reduce—Reuse—Recycle when developing management strategies.
Reduce
The first goal in stormwater management must be to reduce the volume of stormwater flowing across hard surfaces in developed areas. Reduced volumes of flowing stormwater mean less pollution is picked up, flooding is less likely, and municipal systems are more likely to be able to detain and properly treat the stormwater that does flow.
The simplest way to reduce stormwater flow is to allow it to return to the soil, where it can quickly return to the natural water (hydrologic) cycle. Since the key here is to avoid inundating (and flooding) any particular patch of ground, it’s critical to establish broad areas of permeable soil where rain can infiltrate as it falls. This can be encouraged by replacing hard surfaces such as asphalt and concrete with permeable surfaces such as porous asphalt, pervious concrete, grid pavers, and interlocking concrete pavers separated by joints or gaps. Used on patios, sidewalks, driveways and parking lots, these pavers allow water to pass through gaps filled with sand or small stones to the underlying soil.
One fundamental of reducing damage associated with flowing stormwater is to manage stormwater close to the location where it fell as rain. Bioswales and other vegetated buffers installed alongside roads and in roadway medians are designed to collect runoff, filter out pollution and allow the water to infiltrate the soil before it’s had a chance to gain volume, velocity, and contamination. Bioswales can be constructed to effectively capture and filter runoff even from relatively large hardscaped areas like streets and parking lots.
Even when all stormwater cannot immediately infiltrate the soil, most practices that reduce stormwater flow have a side benefit of improving the quality of water that is collected, whether the eventual disposition is for aquifer recharge or treatment and recycling to drinking water.
Reuse
Both rainwater and stormwater can be reused, ideally with little or no need for treatment if the source and end-use are carefully matched. This kind of reuse takes a minimal amount of energy and resources, making it an ideal option for sustainable stormwater management.
Stormwater harvesting, for example, is a critical tool for maximizing both reuse and recycling and is part of a larger concept of water reuse. In broad terms, water reuse involves collecting and distributing stormwater, graywater, and blackwater to meet different types of water demands. Some typical uses for captured stormwater and graywater water include:
- Irrigation for farms and home gardens
- Municipal irrigation such as for parks and medians
- Process water for industrial activities, manufacturing, and power generation
- Indoor uses such as toilet flushing
Recycle
Recycling of municipal wastewater is already employed in developed countries, through the use of wastewater treatment plants. These plants may deal exclusively with sewage, or they may handle other, less challenging sources like stormwater and some industrial wastewater. These treatment processes can be expensive, however, and it’s not always necessary to aim for drinking water quality.
Good stormwater management techniques, aside from reducing the overall volume of stormwater, can improve the quality of the remaining water. With higher quality water, less treatment is necessary before it can be directed for safe re-use. Lower demands for treatment save energy, require fewer facilities, and reduce costs. These are all important elements in establishing a long-term sustainability plan.
In the overall discussion of stormwater management, it’s common to discuss a variety of well-recognized Best Management Practices (BMPs) that are known to achieve certain goals. BMPs for stormwater management include structural systems, vegetative materials, and management practices focused on preventing, reducing, and treating water pollution.
What About Stormwater Harvesting?
Stormwater harvesting involves both the reuse and the recycle segments of the three Rs. Ideally, systems are designed to direct water towards reuse whenever possible, based on the quality of the water connected. Relatively clean stormwater used to water lawns and landscaping whenever dry weather hits ultimately returns water to the hydrologic cycle without spending energy and resources for unnecessary treatment. Rainwater, especially from green roofs, is usually clean enough to be filtered and disinfected for drinking water with relatively few steps.
Intelligent stormwater harvesting reduces our need to rely on expensive and increasingly scarce potable water for tasks like flushing toilets and washing cars. This is a critical benefit in many cities where the demand for water is approaching, and even exceeding, sustainable limits.
In ever-expanding urban environments, the prevalence of hard surfaces coupled with more frequent severe storm events create a dangerous combination of heavy peak flows and increasing volume. By diverting significant volumes of stormwater that would otherwise flow through city streets, harvesting practices help reduce stress on existing stormwater infrastructure and reduce overall energy consumption.
Moreover, stormwater harvesting offers even more benefits beyond simply providing a readily available supply with which to water the landscaping. In fact, stormwater and rainwater harvesting and reuse can maintain and improve the ability of water to move naturally through watersheds and maintain the hydrologic cycle. The use of BMPs and green infrastructure in stormwater management reduces many of the harmful effects of urbanization, including reducing the amount and types of pollutants carried into surface waters, minimizing the destructive effects of erosion, and protecting the health of vulnerable aquatic ecosystems.
