The most serious environmental threat that cities and towns face is urban flooding. This threat will likely increase in the future as extreme rainfall changes.
Urban flooding is a major problem caused by the urbanization process. Stormwater cannot penetrate buildings, roads, and pavements. The amount of stormwater the urban landscape is able to retain or infiltrate will be exceeded, and water will start to flow downhill.
Stormwater runoff, in addition to flooding, is a leading cause of contamination and ecological degradation of urban streams. It is a key element in the restoration and protection of our waterways.
In our busy cities, it is becoming more popular to pave front yards in order to create parking spaces. Water runoff from private homes can increase. Courtesy Alessandro Ossola
Urban flooding
Urban areas generate large amounts of stormwater runoff from impervious surfaces on private residential land, such as rooftops and patios.
According to the work we performed for the City of Melbourne in Melbourne, Australia, in the past, the amount of stormwater produced by a typical urban parcel is approximately 83,000 liters annually (assuming an impervious surface area of 250 square meters).
Residential gardens are more water-permeable than public parks and nature reserves in cities.
The area that is cultivated in the United States with corn – the largest irrigated crop – is about three times the area covered by urban lawns.
Around 6,733,600 Australian households have a Garden. This compares to approximately 52,000 Recreational Parks and Reserves.
The backyard is dead.
Our gardens are rapidly changing due to new economic and social norms. Researchers in Leeds, UK, found that paving residential gardens increased by 13% during 33 years (1971-2004). This led to a 12% rise in runoff.
Lack of time and interest is also a reason why people are losing interest in gardening. The ” Death of the Australian Backyard ” may also be underway in Australia, where new houses are being built at the expense of our gardens.
These green spaces, even though they are shrinking, still provide valuable benefits to the public and private sectors, especially if they are managed with water-sensitive practices.
Our gardens can capture stormwater that is generated by impervious surfaces, allowing us to disconnect residential properties from municipal sewers. Gardening is also common in urban areas, which helps to manage stormwater runoff.
Water-sensitive gardening
The gardens in your home can act as sponges. Plants can absorb water from the air and leave when it rains. Rainwater can percolate into the soil or evaporate and return to the atmosphere. The rest of the water is lost through superficial runoff.
By planting more trees, grasses, and shrubs in our gardens, we can intercept larger amounts of stormwater. This will cause water to be evaporated through the vegetation.
Reduce runoff by allowing mulch to accumulate or using techniques such as differential mowing.
Gardening with trees, shrubs, and grasses can intercept large volumes of rainfall, reducing runoff into sewage systems and rivers. This type of vegetation helps cool buildings in summer and reduces energy consumption. Courtesy Alessandro Ossola
Rain gardens are water-sensitive designs made of a porous substrate (for instance, 50 cm of loamy soil) and native plants (or vegetables).
Stormwater diverted into rain gardens will usually pool up to a depth between 20-30 cm before it is diverted from the drainage system. You can achieve this by surrounding the garden with raised wooden edges, which will improve system performance.
It is easy to use rain gardens to intercept stormwater from a Melbourne household. Installing a small rain garden of 10 square meters could reduce the amount of stormwater that is transported downstream from 83,000 liters to 15,000 liters. This is close to an 81 percent reduction.
Rain gardens allow stormwater to be absorbed back into the ground. It can also provide soil water to nearby plants, reducing the need for drinking water during dry seasons.
A private garden covered with synthetic turf. This lawn is not pavement, but it still has an impervious surface that prevents water from percolating into the soil, contributing to increased stormwater runoff. Courtesy Alessandro Ossola
Locally, many city councils and environmental groups have also begun to recognize the importance of depaving neighborhoods in order to create healthier and greener cities. In the United States, the Philadelphia Water Department offers advice to homeowners on removing paving from their backyard. Depave is a Portland-based group that aims to remove paved areas from local neighborhoods by engaging and involving the community.
Private gardens are more than just a place to escape the bustle and noise of cities. Our gardens are part of the solution for some of our most pressing environmental problems in cities, like stormwater management.
