FIELD ANALYSIS OF THE WATER FILM DYNAMICS ON A ROAD PAVEMENT

The analysis of water film dynamics on road pavement during high intensity rainfall events is fundamental in the study of problems of different nature, from road safety to urban drainage. The influence of precipitation time-variability and road pavement geometry on the water film dynamics is investigated using an experimental monitoring station installed on a mountain road which is prone to heavy storms. The monitoring station is composed by a road portion, a rain gauge and a video-camera automatically activated during intense rainfall. The investigation is based on the digital analysis of the recorded images between summer and autumn 1999. The water film surface irregularities, due to the raindrop impact with the surface and to the presence of roll waves, are studied. The first results are relative to the analysis of the roll-waves dynamics, as they are prevalent in terms of visible effects during the periods of intense rainfall. The digital analysis of the image sequences allows estimating direction and speed of the wave propagation with variable precision due to different light conditions. Using empirical relationships derived from laboratory experiments (Caporali et al., 2000b), and a high-resolution Digital Terrain Model (DTM) of the road surface, depth and discharge of the water film in the maximum local slope direction are investigated.