As urban and suburban areas grow, so too does the amount of impervious surfaces from roads, parking lots, roofs, houses, and more. This puts an increasing amount of pressure on parks, natural areas, urban forests, open space, and lawns to capture rainfall and reduce stormflow into nearby watersheds. Not only do plants reduce stormflow, but did you know that they also cleanse it? Rapid urbanization increases the variety and amount of pollutants that can be found in water. As rainfall hits impervious services, it picks up various urban pollutants such as petroleum products, pharmaceuticals, personal care products, industrial discharge, sediment, road salts, heavy metals, chemicals from cars and trucks, and more.
Green infrastructure, including lawns, takes advantage of natural plant processes such as infiltration, evaporation, and transpiration to keep water and pollutants out of stormflow and allow it to enter the natural water cycle. Perennial grasses and their fibrous root systems are some of the most effective species of plants at fracturing compacted, mineral soils and depositing organic carbon through photosynthesis. As they do this, they naturally increase the amount of pore space in soils capable of holding oxygen and water. Want to learn more about the value of grass lawns at capturing rainfall, reducing stormflow, and more? Check out some of the highlights from recent scientific research below!
Lawns and Urban Water
- A 5,000 sq. ft. natural grass lawn has the potential to capture around 2000 gallons of rainwater before runoff occurs on sandy-loam soil, and up to 27,000 gallons of rainwater before runoff occurs on sandy soil.
- The thatch alone on a 5,000 sq. ft. lawn can capture 500 gallons of rainfall before runoff occurs.
- Grass lawns provide ecosystem services including water filtration, sediment reduction, runoff control, flood control, and reduction in point and non-point source pollution,
- A recent study of a typical metropolitan area with a population of 407,000 people demonstrates that low-density, residential lots with a range of 50 to 80% vegetation including lawns provided the greatest overall infiltration among various land-cover classes.
- In the same study as above, open spaces such as city parks, golf courses, and cemeteries comprised of lawn grasses were the second highest land-cover class in their ability to regulate urban runoff.
- A doubling of grass blade density results in a 2-fold increase in infiltration rate and 66% reduction in runoff.
- The complex system of grass leaves, stems, and thatch creates hydraulic resistance to lateral water flow, which increases surface residence time and infiltration into soil, thereby reducing runoff velocity and amount.
- Natural grass lawn ecosystems support abundant populations of edaphic organisms including earthworms, which combined with grass’s highly dense root system increases soil macropore space and contributes to higher soil water infiltration rates and water-retention capacity compared to other landscape types.
- The extremely dense and fibrous root system of grass lawns act as a biological filter, trapping and removing non-point source pollutants before they enter groundwater supplies.
- Natural grass is often used in catchment and filtration areas in urban areas due to its ability to trap pollutants including heavy metals, oils, grease and fuels, and household/industrial hazardous wastes before they enter surface waters.
- Of 11 pharmaceutical pollutants contained in recycled wastewater, none were detectable in drainage water leaving grass lawns highlighting the tremendous capacity of natural grass systems for filtering and purifying groundwater and role of grass lawns and other areas in environmental protection.
- The presence of natural grass has been shown to reduce runoff and soil losses from erosion from 6 to 18 times greater than bare soil.
- Natural grass leaves dissipate a large amount of the energy of falling raindrops, thus slowing the rate of runoff flow.