Stormwater runoff is generated when natural precipitation – rain, snow, ice melt, etc. – does not initially infiltrate/percolate into the ground. When precipitation is absorbed into the soil, vegetation draws some of the water up through its roots, but the remaining liquid continues its journey deeper into the soil to replenish aquifers and other underground water sources. Stormwater may collect into puddles or flow across the land’s surface, as runoff, into larger bodies of water such as ponds, lakes, streams, rivers or wetlands. Most surface runoff flows, untreated, into nearby rivers, streams and other surface water bodies – carrying with it eroded soil, debris, bacteria, chemicals and other pollutants. These pollutants may result in a variety of water quality problems including:
- floating debris and trash
- fish kills
- algal blooms
- higher drinking water treatment costs
Common pollutants and contaminants are picked up as water flows through streets and parking lots, from fertilizers and pesticides used on lawns and vegetation, and from the soil that eroded during the flow of water over unprotected and unvegetated bare ground.
When the soil becomes saturated, or when precipitation falls onto manmade impervious surfaces such as paved streets and parking lots, the excess water runs across the surface and flows into ditches, storm drains and sewers. In developed environments with many impervious surfaces, unmanaged stormwater can cause two serious problems -- flooding and potential water contamination.
As populations and the demand for water increases, stormwater management becomes even more important. In drought-prone and arid climates, water management, purification and harvesting is particularly important to create self-sustaining water resources for urban environments.
The purpose of stormwater management in urban environments has become broader over time. Although flood mitigation continues to be an important factor, many other concerns are influenced by stormwater management. Stormwater management strategies and practices have evolved beyond pipe-based drainage systems into multifunctional systems that meet ecological and social objectives.
Stormwater management is one of the most difficult challenges that both rural and urban communities face. Some cities use classic catch basin systems, with only a grate or manhole cover visible at ground level. Underground, hidden from sight, are areas that can easily become clogged or leak, often leading to serious damage and cost. Many cities, however, are abandoning the old-fashioned, precast, concrete catch basin and its associated problems and utilizing flexible, impermeable liners to create custom-built catch basins and other features within the stormwater management system.
How Does Stormwater Management Help?
All too often, stormwater is treated as a nuisance rather than an important resource. Although runoff issues exist, the water is essential to recharge underground water sources. Without adequate stormwater management processes in place, flooding occurs, wells dry up, local rivers lose volume and waterways become contaminated.
Where urban development has led to the installation of many impervious surfaces such as paved streets, buildings and hard-surface parking lots, precipitation is not allowed to naturally soak into the ground. Instead, in these settings, excess precipitation collects and flows into drainage ditches, storm drains and sewer systems. Insufficient and inadequately planned stormwater management systems can result in flooding and unsanitary, polluted and contaminated water collection.
The main purpose of stormwater management is to detain/retain stormwater and remove the contaminants and pollutants that are often present in the water. This is achieved through:
- the incorporation of pervious surfaces that allow precipitation to soak into the soil
- the installation of gutters, culverts, piped drainage and storm sewers (gray infrastructure)
- protecting and restoring methods of stormwater management that mimic the natural water cycle (blue/green infrastructure)
Stormwater management, which must be compliant with local, state and federal regulations, has municipal, industrial, commercial and construction applications. Failure to comply with, or totally ignoring, these regulations often results in additional fees and exorbitant costs to repair the systems. The National Pollutant Discharge Elimination System (NPDES) addresses all levels of stormwater regulations and can assist you in determining the rules and regulations which apply to your particular small (one to five acres) development project. Larger projects generally staff engineers who are well-versed in local, state and federal guidelines and regulations.