Influence of time-space rainfall variability on urban runoff models: the Mostacciano catchment case study

For a correct design and construction of an urban drainage system it is necessary a good knowledge of urban hydrological problems and drainage processes. The hydraulic and hydrological phenomena of an urban catchment are directly linked to a large number of factors: climatic pattern of the region where the basin is located, rainfall time-space variability, and physical characteristics of the catchment. In order to investigate on these phenomena the availability of data from experimental basins can play an important role for the growth of the knowledge. For this reason in the present paper we deal with a field investigation, carried out during an eight-year period (from 1985 to 1993) in the “NIR-Mostacciano” urban test catchment, located in the outskirts of Rome. This watershed drains a residential area and for its geomorphological and environmental characteristics, it can represent a typical situation in the Italian urban context. It is also well known as in rainfall studies for urban storm drainage planning maximum intensities for short durations are involved. In addiction the errors in hyetograph input due to different spatial resolution are amplified by losses and flow processes so that they result in bigger errors in runoff volumes and peak discharges (Paoletti, 1993). To take into account of the time-space rainfall variability the measurements of the two raingauges operating in the catchment are integrated with the raingauges network of the National Hydrographic Service that is quite dense around the case-study area. The experimental results have ascertained that this catchment denotes a very quick response to the hydrological input, with the consequential necessity to use data with a very high resolution. To link the precipitation measurements to the discharge ones a rainfall-runoff model is calibrated by the use of data with very high spatial and temporal resolution; the results are showed in the paper.