How Does Your Garden Flow? The Impact of Domestic Front Gardens on Urban Flooding.

Aims: To quantify rainwater runoff from domestic front gardens as a consequence of increased impervious surface area and climate change impacts, thus allowing the runoff contribution from both newly and previously covered front gardens to be assessed in terms of the overall urban flood burden. Study Design: Numerical simulation of the runoff from a typical front garden in response to simulated rainfall events for four UK cities (Edinburgh, Manchester, London, and Exeter). Methodology: A typical front garden was simulated with varying areas of impermeable surface area (0%, 10%, 25%, 50%, 75%, and 100%) to represent observed trends in garden paving. Storm events representing current design and projected future rainfall intensities were applied to each of the four cities. The resultant runoff volumes were then quantified. Results: Runoff is shown to be directly proportional to both the impermeable surface area and the rainfall intensity. Areas of impermeable paving can generate substantial volumes of runoff during a storm event which can contribute to localized flooding or add to the urban flood burden. Increased rainfall intensities and frequencies due to climate change are likely to increase runoff further. Conclusion: Domestic front gardens play a vital role in managing surface water runoff in towns and cities. Growing trends of paving over front gardens put this role in jeopardy, while increasing rainfall intensities due to climate change make this role increasingly important. The quantification of domestic front garden runoff provides a mechanism for facilitating the protection, and enhancement, of this important asset in terms of water and urban flood management.