Abstract
Rainfall simulators are useful tools for controlling the main variables that govern natural rainfall. In this study, a new drop-forming rainfall simulator, which consists of pressure-compensating dripper grids above a horizontal mesh that breaks and distributes raindrops, was developed to be applied in wash-off experiments in a large-scale physical model of 36 m2. The mesh typology and size, and its distance to drippers, were established through a calibration where rain uniformity and distributions of raindrop sizes and velocities were compared with local natural rainfall. Finally, the rain properties of the final solution were measured for the three rain intensities that the rainfall simulator is able to generate (30, 50 and 80 mm/h), obtaining almost uniform rainfalls with uniformity coefficients of 81%, 89% and 91%, respectively. This, together with the very suitable raindrop size distribution obtained, and the raindrop velocities of around 87.5% of the terminal velocity for the mean raindrop diameter, makes the proposed solution optimal for wash-off studies, where rain properties are key in the detachment of particles. In addition, the flexibility seen in controlling rain characteristics increases the value of the proposed design in that it is adaptable to a wide range of studies.
Highlights
Urban areas of cities are expected to continue to grow significantly over the forthcoming decades [1].The sustainable development of cities, respect for the surrounding environment, and ensuring healthy living conditions are all significant challenges for current science and engineering
This study focuses on the development of a new drop-forming rainfall simulator to study wash-off and sediment transport processes in the 36 m2 urban drainage physical model presented in Naves et al [25]
Local rain properties registered by the disdrometer are presented here to be used as reference
Summary
Urban areas of cities are expected to continue to grow significantly over the forthcoming decades [1].The sustainable development of cities, respect for the surrounding environment, and ensuring healthy living conditions are all significant challenges for current science and engineering. Increases in the percentage of impervious areas in urbanization processes leads to higher runoff volumes and flow discharges, and to an increase in the total load and peak concentration of mobilized pollutants. These contaminants, such as heavy metals, polycyclic aromatic hydrocarbons (PAH) and microplastics, accumulate in urban catchments during dry weather and can be washed off during rain events and transported by stormwater runoff into drainage systems, and eventually into aquatic media [2,3,4]. Since the impact of these pollutants in receiving environments represents one of the most urgent environmental issues in urban areas [5,6], a thorough understanding of processes involved in wash-off and sediment transport is essential in estimating pollution loads and concentrations toward designing treatment and management measures that promote the sustainable growth of towns and cities.
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