How Your Garden Could Help Stop City Flooding

gardening

urban gardening1 5 14

Urban flooding represents the most common yet severe environmental threat to cities and towns worldwide. Future changes in rainfall extremes are likely to increase this threat, even in areas that could become drier.

The urbanisation process itself is one of the major causes of urban flooding. Buildings, pavements and road areas are impervious to stormwater. When the amount of stormwater that the urban landscape can retain or infiltrate is exceeded, water starts to flow downhill, generating runoff.

Besides flooding, stormwater runoff is also a major cause of pollution and ecological degradation of urban streams. Reducing the amount of stormwater runoff conveyed to stormwater pipes is central to the restoration and protection of our waterways.

gardeningPaving front yards is an increasingly popular practice to create car spaces in our busy cities. This can increase water runoff from private households. Courtesy Alessandro Ossola.

Urban flooding

In urban areas, large volumes of stormwater runoff are generated from impervious surfaces located on private residential land, such as roofs and our beloved backyard patios.

For example, based on work we did for the City of Melbourne, even in very dry years the average amount of stormwater generated from a typical urban land parcel in Melbourne, Australia, is about 83,000 litres per year (assuming a total impervious area of 250 square metres).

On the other hand, residential gardens make up more green space in total than urban public parks or nature reserves, making backyards essential water-permeable areas within cities.

In the United States, it is estimated that urban lawns cover an area of about 128,000 square km - about three times the area cultivated with corn, the US’s largest irrigated crop.

In Australia, 83.5% of households - or about 6,733,600 homes - have a garden, compared with roughly 52,000 recreational parks and reserves.

The death of the backyard

Unfortunately, our gardens are quickly changing under new economic drivers and social norms. Researchers found that paving of residential gardens in Leeds, UK, increased by 13% over a period of 33 years (1971-2004). That generated a 12% increase in runoff from the same gardens.

People are also getting detached from gardening due to lack of time and interest. Similar to Britain, the “death of the Australian backyard” may be under way here too, as newly built houses are growing bigger at the expense of our gardens.

Despite the shrinkage of residential gardens, these green spaces still offer valuable private and public benefits, particularly if managed in a water-sensitive way.

Stormwater generated by impermeable surfaces can be captured in our gardens, disconnecting residential properties from municipal sewer systems. Gardens are also widespread across the urban landscape, helping in the decentralised management of urban stormwater runoff.

Creating a water-sensitive garden

Residential gardens can act like sponges. When it rains, plants intercept water on leaves and canopies. Rainwater can then percolate through the soil or evaporate back into the atmosphere. The remaining water is lost as superficial runoff.

Planting more trees, shrubs and grasses in our gardens would help to intercept greater amounts of stormwater, causing water to be transpired back into the atmosphere through the vegetation.

Allowing mulch and leaf litter to accumulate, or using practices such as differential mowing, could also help to reduce runoff.

 Gardens with dense vegetation made of trees, shrubs and grasses intercept substantial volumes of rainwater, decreasing runoff reaching sewage systems and waterways. This type of vegetation also helps to cool buildings during summer, reducing energy consumption. Courtesy Alessandro Ossola Gardens with dense vegetation made of trees, shrubs and grasses intercept substantial volumes of rainwater, decreasing runoff reaching sewage systems and waterways. This type of vegetation also helps to cool buildings during summer, reducing energy consumption. Courtesy Alessandro Ossola“Rain gardens” are water-sensitive designs composed of a highly porous substrate (for example 50 cm of loamy sand) planted with native vegetation (or even vegetables).

Usually, stormwater diverted to rain gardens is allowed to pool to a depth of 20-30 cm before any overflow is diverted back to the drainage system. This can be achieved by surrounding the rain garden with raised wooden edging which greatly improves system performance.

Rain gardens can be easily used to intercept the stormwater generated from a typical Melbourne household. By installing a rain garden as small as 10 square metres, the amount of stormwater conveyed downstream could be reduced from approximately 83,000 litres per year to around 15,000 litres per year. This represents close to an 81% reduction.

In rain gardens, most of the intercepted stormwater is infiltrated back into the soil. This can provide nearby vegetation with soil water, helping to decrease the use of drinking water for irrigation (particularly during dry periods). 

A private garden with a lawn covered in synthetic turf. While not considered a proper pavement, this lawn still represents an impervious area not allowing water to percolate into the soil and contributing to increased superficial stormwater runoff. Courtesy Alessandro OssolaAt the local level, numerous city councils and green groups are also starting to recognise the importance of de-paving our neighbourhoods to create greener and healthier cities. For example, in the United States, Philadelphia’s Water Department, offers advice to landlords on de-paving your backyard. Depave, a Portland-based environmental group, also aims to remove unnecessary paved areas in local neighbourhoods through community engagement and participation.

Our private gardens are much more than refuges from the hustle and bustle of modern cities. They are part of the solution to some of our most pressing urban environmental problems, such as stormwater management.

Fortunately, there are numerous ways we can make each garden a water-sensitive one.

About The Authors

Alessandro Ossola, Researcher in Urban Ecology, University of Melbourne. His research focuses in unravelling the functional links between habitat structure, biodiversity and eco-hydrological processes in both natural and human-dominated ecosystems.

Matthew Burns is a postgraduate research fellow working in hydrology and environmental engineering in the Waterway Ecosystem Research Group at the University of Melbourne.

This article was originally published on The Conversation. Read the original article.

Related Books

The Essential Urban Farmer

gardeningAuthor: Novella Carpenter
Binding: Paperback
Features:
  • Penguin Books

Brand: Penguin Books
Studio: Penguin Books
Label: Penguin Books
Publisher: Penguin Books
Manufacturer: Penguin Books

Buy Now
Editorial Review: The "how-to" guide for a new generation of farmers from the author of Farm City and a leading urban garden educator.

In this indispensable guide, Farm City author Novella Carpenter and Willow Rosenthal share their experience as successful urban farmers and provide practical blueprints-complete with rich visual material-for novice and experienced growers looking to bring the principles of ethical food to the city streets. The Essential Urban Farmer guides readers from day one to market day, advising on how to find the perfect site, design a landscape, and cultivate crops. For anyone who has ever grown herbs on windowsills, or tomatoes on fire escapes, this is an invaluable volume with the potential to change our menus, our health, and our cities forever.





Urban Jungle: Living and Styling with Plants

gardeningAuthor: Igor Josifovic
Binding: Hardcover
Features:
  • Callwey Verlag

Brand: Callwey Verlag
Studio: Callwey Verlag
Label: Callwey Verlag
Publisher: Callwey Verlag
Manufacturer: Callwey Verlag

Buy Now
Editorial Review:
  • Provides all your DIY ideas for styling and tips on how to plant
  • Inspiration for seasoned plant lovers as well as beginners, providing the total package on the topic of living with plants
Urban Jungle: Living and Styling with Plants is a source of inspiration, ideas and a manual for all of those who want to bring more plants into their home.

The book guides the reader through different "green" homes in five European countries and shows how beautiful, unique, creative and even artistic living with plants can be. More than that the reader finds endless ideas for styling from the bloggers of the "Urban Jungle Bloggers" community. To complete the topic of indoor plants the book offers easy help for taking care of the plants and DIY tips.




All New Square Foot Gardening II: The Revolutionary Way to Grow More in Less Space

gardeningAuthor: Mel Bartholomew
Binding: Paperback
Features:
  • China

Brand: Hachette/Quarto Publishing
Studio: Cool Springs Press
Label: Cool Springs Press
Publisher: Cool Springs Press
Manufacturer: Cool Springs Press

Buy Now
Editorial Review:

Square Foot Gardening is the most practical, foolproof way to grow a home garden, whether you're growing an urban garden, or have an entire backyard.

That explains why author and gardening innovator Mel Bartholomew has sold more than two million books teaching how to become a successful DIY square foot gardener. Mel developed his techniques back in the early 1980s and has been teaching them around the world ever since. In the process, he has made improvements and refinements, and has continually adapted his practices to keep pace with modern times.

In this second edition, Bartholomew furthers his discussion on one of the most popular gardening trends today: vertical gardening. He also explains how you can make gardening fun for kids by teaching them the square foot method. Rich with new, full-color images and updated tips for selecting materials, this highly produced edition will bring you up to speed with Mel's industry-changing insights.





gardening
enafarzh-CNzh-TWtlfrdehiiditjamsptrues

follow InnerSelf on

google-plus-iconfacebook-icontwitter-iconrss-icon

 Get The Latest By Email

{emailcloak=off}

follow InnerSelf on

google-plus-iconfacebook-icontwitter-iconrss-icon

 Get The Latest By Email

{emailcloak=off}