The process of urbanisation is among the main reasons for urban flooding. Roads, pavements and buildings areas are inaccessible to stormwater. If there is a limit to the quantity of rainwater the urban landscape can hold or absorb is greater than the amount that it can hold the water begins to flow downhill, creating runoff.
In addition to flooding, stormwater runoff can be also a major source of polluting and the degradation in urban waterways. The reduction of stormwater runoff being pumped to stormwater pipes is crucial to the preservation and restoration of our rivers and waterways.
The paving of front lawns is becoming a frequent practice to create parking spaces in busy cities. This could increase the amount of water that runs off from private residences. Courtesy Alessandro Ossola
Urban flooding
Urban areas are where huge quantities of stormwater runoff are produced from impervious surfaces on private property like roofs and our backyard patios that we love so much.
Based on the work we conducted on behalf of Melbourne, based on work we did for the City of Melbourne, even in extremely dry seasons, the amount of stormwater produced from a suburban land plot within Melbourne, Australia, is around 83,000 liters a year (assuming that the total impervious area of 250 square meters).
However, the gardens of residential properties comprise the most green spaces than public parks in urban areas or nature reserves. This makes backyards crucial water-permeable spaces within urban areas.
In the United States, it is believed that the lawns of urban areas are spread over an area of around 128,000 square kilometers – roughly three times that of the land planted with corn, which is the country’s biggest irrigation-irrigated crop.
The statistics show that in Australia, 83.5% of households, or roughly 6,733,600 houses, are home to an outdoor garden, which is a lot more than 52,000 recreation parks and reserves.
The end of the backyard
Unfortunately, our gardens are rapidly changing in response to the new economic trends and social standards. Researchers have found that the amount of paving for gardens in residential areas located in Leeds, UK, increased by 13% in a span that spanned three decades (1971-2004). The result was an increase of 12% in runoff coming from those gardens.
Many people are becoming disengaged from their gardens due to lack of interest and time. Like Britain in this regard, we are experiencing the ” death of the Australian backyard” might be afoot in Australia as well, since newly constructed homes are expanding and destroying our backyards.
Despite the decline of the gardens used by residents, These green spaces provide valuable public and private advantages, especially if they are maintained in a way that is water-sensitive.
The impermeable surface of a stormwater drain could be collected in our gardens, separating homeowners from municipal sewers. Gardens are also common throughout cities, aiding in the decentralised administration for urban runoff stormwater.
Designing a water-sensitive garden
The gardens of residential areas can behave like sponges. When it rains, the plants take in water that has fallen on leaves and canopy. Rainwater then can percolate through the soil or evaporate into the air. The rest of the water goes away in the form of superficial runoff.
The addition of more trees, shrubs, or grasses around our yards will aid in absorbing more stormwater and causing it to evaporate back into the atmosphere via the plants.
allowing mulch or leaves to build up by using techniques like the practice of differential mows could help to decrease runoff.
Gardens with dense vegetation comprised of shrubs, trees and grasses catch large quantities of rainwater. This reduces the amount of runoff that reaches sewage systems and waterways. This kind of vegetation can also help cool buildings in summer and reduce energy use. Courtesy Alessandro Ossola
“Rain gardens” are water-sensitive designs that are made up of a porous substrate (for instance, 50cm of loamy sand) filled with native plants (or maybe veggies).
Typically, stormwater that is diverted to rain gardens can accumulate to an extent of 20-30 centimeters before being returned to the drain system. This can be accomplished by enclosing the park with a raised wooden edge, which significantly improves the efficiency of the system.
Rain gardens can easily be utilized to catch stormwater that is generated by the common Melbourne household. With the installation of an area as tiny as 10 square meters and a small quantity of stormwater that flows downstream could be reduced by around 83,000 liters to about 15,000 liters a year. This is nearly an 81 percent reduction.
In the rain gardens, the majority of the stormwater that is intercepted is absorbed back into the soil. This could provide the surrounding vegetation with water from the ground, helping to cut down on the use of drinking water to rinse (particularly during dry seasons).
