Importance of front gardens in flooding battle
Recent storms in the UK have highlighted the vulnerability of many urban areas to high levels of rain. Whilst research suggests climate change will result in hotter, drier summers in the UK, it has also warned the rain which punctuates this heat is likely to fall in heavier bursts. Without management in the future, urban flooding is therefore likely to occur during periods of heavier rainfall in summer as well as the winter.
Together with amenity planting and greenspaces, gardens attached to domestic homes in urban areas have the potential to play a key role in reducing the severity of flooding during storm events.
Surface runoff is defined as the flow of water on the ground surface when excess rainwater falls and can no longer infiltrate the soil. It is more likely to occur where impervious surfaces such as traditional tarmac pavements and driveways do not allow water to soak into the ground and is a primary cause of urban flooding.
Research suggests domestic gardens make up a significant proportion of the greenspace in towns and cities, and therefore have the potential to reduce the severity of urban flooding by reducing surface runoff and increasing infiltration. Whilst generally smaller than the rear garden, the front garden of urban properties can play a key role in reducing runoff. The reality, however, is that the front gardens of many houses in urban areas are being paved over for use as a driveway.
A 2016 study by Heriot Watt University revealed a typical front garden with no impermeable paving was found to produce no runoff in response to both 1 in 5- year and 1 in 50-year storm events. The addition of a small area of impermeable surface resulted in runoff.
The same research paper suggested a typical front garden in London is more likely to generate higher runoff volumes than cities in other regions due to the higher rainfall intensities applicable to the south-east. For example, the current 1 in 5-year event in London is equivalent – in terms of runoff volume – to a 1 in 50 year event in Edinburgh.
Predictably, forecasted increases in rainfall intensity will have the effect of increasing runoff from front gardens throughout the UK, which means the contribution of paved front gardens to the overall surface runoff volume will also increase.
Reducing the surface area of impermeable surfaces in front gardens in urban areas is not straightforward, given the trend for car ownership and desire to park on a driveway.
Whilst planning regulations have been changed to reduce further loss of permeable surfaces, there is evidence these are not enforced, and there is no legislation to target the gardens that have already been covered with an impermeable surface.
Educating homeowners about the role front gardens can play in the urban landscape in terms of rainwater management and providing them with advice on how this can be achieved, is likely to present the most reliable solution at present. The range of permeable surfaces now available means homeowners can still create a driveway on their front garden, without significantly increasing surface runoff.
Financial incentives may also play a role in encouraging homeowners to re-consider using impermeable surfaces. Evidence suggests house prices may reduce once most front gardens on a street have been paved over, as the result is a less attractive street scene to home buyers. More importantly, however, is the likely effect of increased urban flooding on household water, sewage bills, as well as insurance premiums.
Association Accredited Suppliers now offer a range of permeable paving products suitable for driveways and any area of hard surface. When constructed correctly, these offer the benefits of traditional hard surfaces without the risk of increased surface water runoff.
Further reading:
How does your garden flow? The impact of domestic front gardens on urban flooding