An investigation into the extent and impacts of hard surfacing of domestic gardens in an area of Leeds, United Kingdom

There is limited information available on the scale and potential impacts of increasing imperviousness in suburban areas, despite significant evidence which suggests that such changes could have severe consequences, particularly for urban flooding. In this investigation, aerial photographs from 1971 to 2004 were used to map changes in the impervious cover of a 1.16 km2 suburban area of Leeds in northern England. A 13% increase in impervious surfaces was observed over the 33-year study period. Of the increase in impervious surfaces, 75% was due to paving of residential front gardens. To allow an assessment of annual runoff sensitivity to the increased imperviousness in the study area, an empirically based model, L-THIA (long-term hydrologic impact assessment model) was applied. The L-THIA hydrologic model predicts that average annual runoff increased by 12% over the period of study. The L-THIA model is also used to create a graph from which increases in annual runoff due to increased imperviousness can be predicted. These results show significant increases in imperviousness and suggest that this will cause an increase in the frequency and magnitude of flooding in the area.