- Polluted runoff is one of the greatest threats to clean water in the U.S.
- Urbanization can reduce groundwater recharge by 30-52%
- Climate change is expected to lead to increased flooding
- Natural drainage systems can improve public health by providing clean air and better quality water
Current Problem
As we combat the effects of climate change on our cities, we have to think of ways to adapt to the issues that arise with it, one of which is extreme weather events. With the increased precipitation we expect, we need new methods that better handle high levels of stormwater.
Currently, the goal of our urban stormwater systems is simple: collect runoff and get it out of the city as fast as possible.
Composed primarily of impervious surfaces, urban drainage systems are full of stormwater that has collected chemicals, bacteria, trash, gasoline, bacteria, and more. In LA, this runoff is carried through concrete channels that eventually drain to the Pacific Ocean. To reduce such high levels of runoff, our approach needs to mimic natural systems. Instead of focusing on water discharge, we need to prioritize water recharge. This is the thinking behind low impact development.
Emerging Solutions
Los Angeles
Low impact development (LID) is the use of sustainable drainage solutions that allow water to follow its natural cycle, replenishing the groundwater table and being uptaken by plants. Examples of low impact development include rain gardens, swales, rainwater harvesting, permeable pavement, and drainage basins. These systems focus on handling stormwater at the source, rather than carrying it miles away to be treated in a wastewater treatment plant, or discharged to nearby water bodies.
Implementing these drainage systems brings a multitude of ecological and social benefits. By allowing water to percolate through the soil, we help to recharge the water table, thus nourishing our water supply and helping prevent drought. As well, these proposed drainage systems support habitats in cities. The green spaces that come with LID can help to increase biodiversity in cities through housing a variety of native plants and creating habitat patches that welcome native fauna. By strengthening the biodiversity of our cities, we increase our climate resilience.
Besides the ecological benefits, green drainage methods bring a variety of social benefits to our communities. Reducing the urban heat island effect, increasing green spaces, and fostering the spread of knowledge are just a few. Focusing on the last point, the development of green drainage systems can be a community-wide effort in which people who benefit from these drainage systems can contribute to their planning, construction, and maintenance. This creates a sense of togetherness and pride in communities, and fosters knowledge sharing.
The South Los Angeles Wetland Park, transformed from a bus yard to a public green space with a constructed wetland habitat, is a great example of a local sustainable urban drainage system. The park’s 4.5 acres of wetlands treats runoff through collecting stormwater, pretreating water in an underground system, and then diverting water to the wetland. The pretreatment system is a hydrodynamic separator that removes heavy metals, trash, sediment, and gasoline. Mimicking the natural filtration properties of wetland ecosystems, the wetland’s open-water, emergent marsh, riparian, and upland plants improve water quality through sediment trapping, nutrient removal, and chemical detoxification. The site also features a bioswale that carries runoff from the parking lot into the wetland. This project brought much needed green space to a neighborhood of Los Angeles that had the second lowest park acreage per capita in the city.
California
The Southeast Community Center in San Francisco is another great example of a nature based drainage solution in the state. In front of the community center lies a green retention basin composed of a variety of native plants and stepping stones. Through the historic atmospheric river events of this past winter, the large bioswale showed its resilience to extreme weather events. While California as a whole was hit quite hard with historic flooding due to the storms, areas like the Southeast Community Center stood their ground, proving how well green drainage systems can handle major rain events by detaining water and reducing the stress on the city’s gray infrastructure. Levels of runoff were 45% lower than they would have been before the site’s redesign.
National
One of the best examples of LID in the United States is in High Point, Seattle. Equipped with one of the largest natural drainage systems in the country, the neighborhood of High Point features bioswales, yard drains, storm drains, rain gardens, and porous pavement that drain to underground slotted pipes. The drainage system flows into a retention pond and then the nearby Longfellow Creek, which is home to an endangered salmon run. When creating this drainage redevelopment, planners were focused on improving the water quality of Longfellow Creek to protect one of the last four remaining salmon runs in Seattle. Before this new system was in place, contaminated stormwater flowed directly into the creek. The redesign converted an area that was once 65% impervious to one with 75-80% infiltration. High Point’s sizable nature-based drainage approach is a great example of how other major US cities can apply LID on a larger scale.
Global
In Copenhagen, Denmark, a residential courtyard at Straussvej was redone in 2021 with the focus of creating rainwater solutions while also providing a green space for the surrounding apartment building’s residents. The design was created in collaboration with residents and the Copenhagen Municipality. Built with recycled building materials, the site features a “climate wall” that carries rainwater into a central pool filled with filtered roof runoff. Before it enters the “climate wall”, runoff is collected and filtered through a limestone filter beneath the green area. This project is the first in Denmark to biologically purify its water to a safe level that allows for recreation within the central pool. The redesigned courtyard also houses a community greenhouse and playground area.
As noted at the top of this page this article was written by Ava Dillard.