How adding plants to your driveway could reduce winter flood risks

When it comes to adapting cities to a rapidly and dramatically changing climate, the garden is on the frontline of the fight. Gardens act as green sinkholes, allowing excess rainwater to escape, as well as helping to cool cities in summer.

Gardens would provide all these (and other) benefits if they were not being concreted over—and research shows this is happening fast. Around 54% of front gardens in the UK are now concreted over, up from 46% in 1991.

As the winter storm season approaches, the risk of flooding is of increasing concern. Urban areas face the double jeopardy of more intense rainfall due to climate change and enhanced soil sealing from paving over of gardens.

At least one in six people in the UK already live with flood risk as heavy rainfall is increasing. Insurance claims linked to extreme weather are rising.

A recent report from the Royal Horticultural Society, launched on October 30, highlighted how UK front gardens now comprise 89,000 hectares of paved or concreted space, compared to only 73,500 hectares of space with plants.

At a wider scale across Europe, it is thought that about 25,000 hectares of urban land, such as gardens, is sealed each year via urban expansion and the use of impermeable surfaces.

The green spaces in cities—gardens, parks, roadside verges and urban woodlands—help stop cities from flooding. Gardens act as conduits to disperse rainwater. They trap and slow rainwater in the first place—acting as a brake on flash flooding and allowing rainwater to find its natural path to the soil water table and flow into our rivers.

Plant canopies, detain and retain rainwater (green sponges in effect) and roots re-route surface water to deeper, safer sub-surface layers (infiltration).

Plants move water from their roots to their leaves and release it as vapor—a process that works like nature’s water pump and air conditioner, cooling cities in summer. This process pumps tons of water back to the atmosphere every day, and in summer, significantly cools the city. The pumping action is important as it allows the soil to dry quickly—essential before the arrival of the next storm. Saturated soils don’t hold excess water any more effectively than concrete, so they need time to recover.

So gardens are one of the best defenses to stop domestic properties from flooding. In built up areas of cities, 55% of rainfall forms surface flow (runoff—the water that potentially enters one’s front door), yet in green areas, there’s only 10% runoff—the rest is absorbed and dissipated by the soil and vegetation. Retaining good plant coverage in gardens and leaving soil open so rain can infiltrate effectively are significant factors in reducing urban flooding.

So why have homeowners decided to pave over and block the natural drains of the city? Turning front gardens into driveways has come from the need to find an off-road spot for the family car as well as a flat surface to place the bins on, and perhaps least justifiably—a place that simply can be kept clean, neat and tidy more easily.

And having an electric car creates more problems, potentially, because that means the car needs to be closer to the house to be recharged, resulting in more paving and concrete close to houses.

Plant your driveway

But there is another way to tackle this: cars and plants can co-exist. Permeable lattice-framed blocks that support the weight of the car can be used to create driveways. These allow plants to grow through the gaps.

Alternatively, gravel pathways and drives can allow access and parking, while providing opportunities for plants to grow around the edges. Many striking garden designs use gravel and scree to grow colorful plants that also support pollinating insects and birds.

Some gardens are even designed specifically to reduce the risk of flooding and exploit plant species that are more effective at trapping and dissipating water. So-called rain gardens help surface runoff water infiltrate into the ground, purifying it in the process. Water is directed off gutters, pavements and roads towards these rain garden soak-aways where it is given time to percolate into the soil. This is where soil and plant root activity help trap silt and deactivate pollutants coming off the road surfaces.

Most people want their car parked close by, but we need to be more imaginative in how we accommodate these vehicles. Driveways don’t need to be simply sterile concrete spaces. Permeability, plants and, indeed, a better sense of place can be built in too, and help reduce flooding along the way.

This article is republished from The Conversation under a Creative Commons license. Read the original article.