Effects of urban afforestation on the reduction of runoff and on the peak flow delay

Abstract

Soil proofng and absence of tree cover produces more volume of surface runoff, enlarges the peak flow and reduces the delay time. The search for alternatives to reduce the volume of surface runoff in urban areas is important to get the hydrological answers to the problems caused by the urbanization process and, along with that, to reduce the risk of flooding. This article proposes to estimate the reduction of runoff and the delay in the peak flow caused by the presence of three species of trees (Mangifera indica, Tabebuia ochracea and Licania tomentosa) in urban areas. This allowed the quantifcation and the performance analysis of tree species in reducing urban runoff; the arboreal parameters correlated with the flow capacity reduction; and examined whether there is reduction and delay in the peak flows. The benefts from the interception of storm water for trees need to be pondered and guaranteed in afforestation master plans and urban drainage in order to reach the mitigation of damage caused by the neglect of urban water. For this, level sensors were used (limnigraphs) to quantify the surface runoff in areas with and without the presence of arboreal coverage, and in experimental structures set on waterproof, semipermeable and permeable soil. For events with an average value of gross precipitation of 17.1 mm, the presence of arboreal individuals caused an average time delay up to the peak flow of 3 minutes, an average reduction of peak flow of 0.8 mm/min and it contributed to an average reduction of surface runoff of 4.7 mm/min.