Low-impact development can manage stormwater

Cities can have many benefits when designed well, including reducing carbon imprints. Another way cities can improve their environmental impact is by using "low-impact development" to manage stormwater. It is also called "green stormwater infrastructure."

Cities can have many benefits when designed well, including reducing carbon imprints. Another way cities can improve their environmental impact is by using “low-impact development” to manage stormwater. It is also called “green stormwater infrastructure.”

The Soil Science Society of America’s (SSSA) September 1st Soils Matter blog explores how low-impact development provides planners with a toolbox of practices and approaches to manage water during rain events and snowmelt.

According to soil scientist and blogger John McMaine, only a small amount of rainfall (10 per cent) becomes runoff on undeveloped lands with no impervious surfaces. The natural landscape and soil manage the rain (or snowmelt) by storing, infiltrating, or evapotranspiration. Runoff becomes a problem in cities where the soil is covered with asphalt for roads, cement and other materials for sidewalks and parking lots. Buildings count, too.

Every time it rains in a city, rainfall hits the pavement and runs into streams, lakes, and ponds. There are few barriers between the source of runoff and the water body. In cities, the water level in streams and flow rates can increase quickly during precipitation events. Streams rise more slowly and over a longer period in natural and country landscapes. Low-impact development replicates the natural water balance by reducing runoff and increasing infiltration.

Managing stormwater and local flooding

A big driver for managing stormwater is to reduce local flooding. While flood reduction is an immediate and critical need, if cities send water downstream using a curb, gutter, and storm sewer system, this relocates the problem rather than resolving it. The low-impact development approach manages stormwater close to a landscape’s natural hydrology or water balance.

Cities can manage local and downstream flooding, and peak flows using low-impact development. Using detention and retention basins, cities can create ways to capture and hold water and release it at a controlled rate. These systems can reduce downstream peak flows but do not reduce the total flow volume. Low-impact development reduces peak flow and total flow volume and improves water quality.

In general, low-impact development works by slowing water down, spreading it out, and soaking it in. Conventional development connects systems of impervious surfaces to send water downstream to mitigate local flooding quickly. An example would be storm drains on a roadway attached to an underground piping system.

Low-impact developments can manage stormwater by capturing, storing, and treating it on-site. Water is held and infiltrates into the ground or distributed across the landscape. Low-impact development approaches can include landscape site design or structural practices.

Sponge cities manage stormwater better

Considering stormwater when a building site is designed could mean disconnecting impervious surfaces. That could include directing roof runoff into a lawn instead of a driveway connected to the street. This allows runoff to soak into the ground instead of just flowing downstream. This is an easy, low-cost way to add function to a landscape to manage stormwater runoff effectively.

Rain gardens and rain barrels are two of the most common strategies for homeowners. Rain gardens, or bioretention cells, are shallow depressions in the landscape that runoff is routed into. The water ponds for 24-48 hours as it slowly soaks into the soil. They are planted with flowers or shrubs that can withstand extremes in water—both flooding and drought. The plants also provide pollinator habitat and aesthetic value. Rain barrels are containers, often 50-gallon barrels, which hold captured rainwater that can be used to water landscaping.

Many options to manage stormwater

Cities, businesses, and institutions can implement a wide range of practices to help manage runoff. Impermeable or impervious, sidewalks, parking lots, and roads can be made porous or permeable. Permeable pavement can be concrete, asphalt, or pavers. They feature a large amount of space that allows water to soak into the pavement. If you’ve seen water rushing off a parking lot during a rainstorm, you can imagine how much runoff can be reduced with permeable or pervious pavement. Medians, boulevards, shoulder areas, and rights of way are great candidates to include pervious pavement.

Homeowners, businesses, or cities can implement low-impact development. Cost does not have to be a barrier when using low-impact strategies. All landscaping costs money. Why not broaden the focus from only visual to functional? Green stormwater infrastructure can provide attractive landscaping features that reduce peak flows and runoff volume. It can improve water quality and, depending on planting types, can also provide habitat for pollinators. It’s time that cities shift their paradigm to use landscapes to meet multiple objectives, not just to look good.

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