How to Slow Down Stormwater in Your Landscape: The First Step in Sustainable Design

Traditional landscaping rushes rainfall off-site as quickly as possible—but this approach harms water quality by increasing downstream flooding and bypassing the natural cleansing that occurs when water filters through soil. Enter "Slow it, spread it, sink it," the sustainable water design mantra coined by Brock Dolman of the Occidental Arts & Ecology Center. This three-step framework guides municipalities and conservation groups nationwide. This article explores the critical first step: slowing water down.

Takt | Studio for Architecture

The Power of Daylighting Water

A quiet revolution is underway among landscape architects who are designing with water more sustainably. A key concept is "daylighting"—bringing water that's confined in underground pipes and culverts up to the surface. Exposed to light, air, soil, and plants, daylighted water naturally cleans itself while slowing down. Slower water means reduced downstream flooding, less erosion, and more opportunity for soil infiltration and natural purification.

Start by identifying where runoff occurs on your property. Any hard surface—roof shingles, asphalt, concrete, rocky outcroppings—sheds water rapidly. Roofs, driveways, and steep slopes are prime culprits. Determine how to intercept water at these points and slow it through storage, permeable surfaces, swales, and strategic plantings.

Rooftop Strategies

The Lewes Building Company

Store Downspout Water

Collecting roof runoff in rain barrels or cisterns removes significant volume from the runoff equation while reducing municipal water dependence. During dry periods, you'll have free irrigation water on hand.

Intercept Runoff with Green Roofs

Feldman Architecture, Inc.

Green roofs offer multiple environmental benefits, but their ability to absorb and retain water during frequent small storms is exceptional. A shallow green roof can capture an inch of rainfall, releasing it slowly through evapotranspiration. This dramatically reduces stormwater loads on downstream water bodies. During larger storms, green roofs also provide initial filtration—runoff from a vegetated roof is cleaner than from an impervious surface.

Driveway Solutions

TOPOS Architects, Inc

Permeable Paving

Permeable paving on driveways and large patios allows water to percolate into the soil while adding visual interest. Water moves slowly through the soil profile, cleaning as it goes, before recharging the aquifer. While permeable paving doesn't absorb 100% of heavy storm volume, surface friction slows excess runoff, providing aeration and more infiltration time. This example features grass-planted concrete pavers designed for vehicle loads, with drainage through each paver's center.

Sloped Site Strategies

Margie Grace - Grace Design Associates

Move Water with Swales

Swales are a cost-effective alternative to pipes and subdrainage for managing stormwater. They make water movement visible, creating a defining landscape feature. A curving, bumpy swale maximizes slowing benefits—curves create meandering flow paths, while rocks and plants break up the surface to aerate the water.

Plant Steep Slopes

Porebski Architects

Plant slopes with herbaceous and woody vegetation to dramatically slow runoff. This reduces erosion, stabilizes the slope, and slows water far more effectively than a mowed lawn.

Vegetate Rocky Surfaces

Island Gardens Company

Natural rock outcroppings shed water like pavement. On steep rocky slopes, water races off unimpeded. Plant alpine species that thrive in minimal soil—even small pockets can establish plants that gradually spread into crevices, breaking up the surface and slowing runoff over time.

Banyon Tree Design Studio

This rain garden at the edge of a permeable driveway captures additional runoff during heavy storms.

Next: How to spread water runoff so it can percolate into the soil.