A methodology to quantify ecohydrological services of street trees

Abstract

This paper proposes a methodology to assess ecohydrological value of isolated trees located in streets and avenues. The study considers two main aspects involved in the reduction of runoff trough interception process: the water volume that can enter the rainwater drainage system and the volume reduction of water needed to be treated in waste water treatment plants. This method uses the Rutter interception model, run at a short time step, to compute street trees interception. The Rational method and dimensionless unit hydrograph (DUH) are used to compute the associated hydrograph at the same time step. The study was applied to street trees located in an urban catchment of Querétaro, one of the main cities of the Altiplano in Mexico. For this purpose the street tree abundance was characterized and rainfall had been recorded at high temporal resolution (5min) for two years. Interception model parameters were derived from results of an interception study conducted on an isolated tree from the Ficus benjamina species. Results show that street trees, as part of the urban forest and in the context of combined sewer systems, allow the reduction and mitigation of overland flux by impervious surfaces by 10–20%, and the peak delay is estimated to 10–15min. The reduction in the volume sent to Waste Water Treatment Plants (WWTP) can be converted into benefits due to lower dimensioning of WWTP.