An urban lysimeter to assess runoff losses on asphalt concrete plates

Hydrological behaviour of roads concerns environmental issues, as pollution by rainwater runoff or urban heat island, and road safety issues. The few studies devoted to the subject concluded that runoff losses are non-negligible and poorly understood. The objective of the study is to better describe runoff losses over asphalt concrete plates of around 0.5 m(2) area. An urban lysimeter has been developed to measure by weighing the partition of rainfall on the plate: storage at the surface and in the pore of the plate, surface runoff, infiltration at the bottom of the plate and evaporation at the surface of the plate. Three plates have been tested outdoor during 5 months each. One of them is a porous asphalt concrete. Results show that runoff losses are significant. They represent 30% of the rain for the traditional plates and 84% of the rain for the porous plate. Losses are mainly due to infiltration (58%) and evaporation (25%) for the porous plate. For traditional plates, evaporation is similar to the one measured for the porous (25% of the rainfall), but infiltration at the bottom is negligible (3%). (C) 2004 Elsevier Ltd. All rights reserved.