by Jill Steed, Ph.D.
Stop and think about what you wash down your driveway or abandon at the curb. Unlike wastewater that goes down a sink or toilet in your home, stormwater is not treated, and often flows directly to a lake, river, or the ocean. In a natural system, stormwater percolates through soil and plant roots, cleaning the water before it enters rivers, wetlands, coastal lagoons, and the ocean. In urban landscapes, impervious surfaces such as roofs, streets, and parking lots prevent the storm water from seeping into the soil. Unfortunately, seemingly innocuous everyday products can be carried from your home to storm drains by rainwater, lawn overwatering or car washing. As the water washes over man-made surfaces, it absorbs the materials collected on the surface such as oil, grease, pesticides, metals, bacteria, viruses and toxic chemicals that have accumulated after many dry months. All this crud washes into the stream and ocean waters with the season’s rain. We call this polluted runoff Stormwater and Urban Runoff Pollution, or SWURP. Originating from city streets, neighborhoods, construction sites, parking lots, and farms miles away, SWURP remains the single biggest threat to water quality in San Diego’s streams, beaches and coastal waters.
You can take steps to reduce the SWURP from your home or business. In addition to using fewer pesticides and fertilizers, picking up litter, purchasing reusable items and cleaning up after your pets, reducing the extent of impervious surface near your home and business is an important source of SWURP control. On a slightly larger scale, you can incorporate low-impact development (LID). LID is a set of building site design and stormwater management practices that reduce runoff and pollutants by means of infiltration, evapotranspiration and reuse of rainwater. Rather than using miles of costly pipes and acres of stormwater ponds, LID techniques manage water and pollutants at the source using natural vegetation and small-scale treatment. LID can be applied to new development, redevelopment, or as retrofits to existing development, and can be used in high density ultra-urban settings as well as low density development. LID solutions include the following:
1. Buffer Strips
Buffer Strips are landscaped areas using particular plants and soil that filter runoff before the water enters a storm drain system or waterway.
2. Cisterns and Rain Barrels
Cisterns and rain barrels are devices that hold storm rainwater runoff in above or below ground storage tanks. This water can be used at a later time for irrigation or other needs.
3. Curbless Parking Lots
Curbless Parking Lots send runoff to adjacent bioretention cells or filter strips to hold and clean the water rather than sending it directly to the storm sewer system.
4. Disconnecting a Downspout
Disconnecting a downspout reduces the amount of rainwater sent into storm sewers and instead channels it onto the ground and into the soil.
5. Green Roofs
Green roofs are roofs planted with a specialized mix of plants in a lightweight soil that can thrive in harsh, dry, and high temperatures on the roof and tolerate short periods of saturation from heavy rains. Green roofs help reduce water pollution from runoff in urbanized areas by absorbing and cleaning rainwater.
6. Permeable Pavement
Permeable pavement contains many small holes, allowing water to pass into the ground. It can be interlocking pavers or can be poured like regular concrete, great for driveways and sidewalks. Rainwater then seeps into the ground or is sent to a rain garden, swale, or infiltration trench.
7. Infiltration Trench
An Infiltration Trench is a rock-filled trench with no outlet that receives stormwater runoff. To help treat and remove the runoff, the stormwater initially passes through a swale, or something similar, before entering the trench. It is then stored in the voids of the stones, slowly seeping through the bottom and into the ground over a few days.
8. Rain Gardens
A Rain Garden is a man-made depression in the ground that collects and stores runoff and is filled with particular plants that help filter and clean the water as it is allowed to seep into the ground. Street gardens near intersections and drain inlets allow runoff to enter a planter through a curb cut and filter through the soil.
9. Swale or Bioswale
A Swale, or bioswale, is a broad, shallow channel with a dense stand of vegetation covering the side slopes and bottom. Swales are designed to trap pollutants, increase groundwater recharge and slow the flow of runoff, which reduces erosion.They are used in lieu of curbs and gutters in low density development.
10. Tree Box Filters
Tree Box Filters are small areas designed to hold runoff beneath trees, where it is cleaned by vegetation and the soil before being sent to the sewer system.
The San Diego Water Board recently drafted a Regional Municipal Separate Storm Sewer System, or MS4, permit as part of a countywide effort to comply with stormwater and urban runoff requirements. Wouldn’t it be great if LID was used in this effort? LID has numerous benefits and advantages over conventional stormwater management approaches. It is a more environmentally friendly technology and a more economically sustainable approach to addressing the impacts of urbanization, and we all know the need for those types of approaches has never been greater. LID also provides the key in its emphasis on controlling or minimizing changes to the local patterns in water flow. To developers, LID can offer infrastructure savings and a way to respond to environmental regulations. For municipalities, LID can help contain burgeoning street and storm water management costs. For community residents, LID can encourage local environmental stewardship. For the environment, the benefits speak for themselves. Great Ecology has experience designing and planning LID for residential and business use, with proven success balancing development and the conservation of natural resources. Give us a call if you are interested in how we can help your business or town reduce its SWURP footprint.