Modelling of road surface pollution buildup and washoff using rainfall simulator

Water quality management of nonpoint source (NPS) pollution is still being confronted with identification and assessment. The extent of pollution due to NPS in tropics is not yet affirmed, and the relative influences of its associated sources were not yet totally understood. This study explored the significance of road as a NPS unit in tropical region of persistent rainfall, and investigated the possible sources of heavy metals in urban areas. To achieve the objectives of this study, the natural rainfall dynamic of the study area was appraised using the flour pellet method. The information was used as a basis for developing a highly efficient Rainfall Simulator (RS) that was used to investigate pollutant washoff process under different rainfall depth and intensities. A total of 30 buildup samples were collected from five chosen roads of varying characteristics, and fractionated into 10 classes of particle sizes each. For quantitative analysis, 60 samples were analysed for dissolved Zn, Fe, Cd, Pb, Cu, Ni, Mn, Al, and Cr concentrations. A multivariate principal component and factor analyses were used to investigate the likely sources of these heavy metals. Three sources were identified, the indigenous, geogenic and scavenge. The natural raindrop sizes were found to vary from less than 1.2 mm to as big as 7.0 mm with median raindrop diameters (D50) of 2.51 mm and a mean of 2.56 mm. These raindrops have an average rain kinetic energy content of 30 J m??2 mm??1. The developed RS can satisfactorily simulate rain intensity similar to natural rainfall, with an average kinetic energy content of 42 J m??2 mm??1 and a D50 between 2.41 and 2.64 mm. An advanced principal component and cluster analysis identified TDS as a surrogate for measuring dissolved metals pollution among eight physicochemical parameters considered, and was therefore used in the modelling of the washoff process. The developed models suggested that the rain intensity plays a more prominent role in the occurrence of first flush, while the rain depth plays a central role in the total washoff event. This research demonstrated that the influence of sediment to retain mass loading did not necessarily translate to higher pollution loading of heavy metals, and the residency of heavy metals in different particle classes cannot be generalised

A novel technique for measuring and sensing rain

Rainfall passing over a given area is a highly dynamic process; it changes constantly in form and intensity. It varies constantly on short spatial and temporal scales that makes real time measurements of the amount of rainfall challenging. Measuring and sensing rain is important to be able to understand and control our urban environment. Traditionally, rainfall analysis for hydrologic modelling use spatial measurements collected at various sparsely spread observation points using rain gauges working on various principles such as weighing type, tipping bucket, capacitive type etc. An accurate representation of spatial model of rainfall is essential for hydrological operational purposes such as forecasting of river flow, flood irrigation planning and modelling of catchment areas. Measurement of drop size distribution are also exploited to investigate microphysics of precipitation and to improve rainfall remote sensing estimation techniques. However, the high initial costs of convectional rain gauges prevent collection of data with high spatial resolution. The research looks at investigating the sensor stack to be a part of an integrated sensor approach to develop a device architecture for the development of low cost integrated rain sensing and measuring the rain.The device architecture consists of three main stacks – energy generation layer, sensing layer, processing layer. The raindrop on impact causes vibration on the device surface. This force exerted by the raindrop causes a deflection and is measured indirectly by the use of a thin film piezo sensor. As part of the work, we find there is a good correlation between the vibrations caused and the size or volume of the raindrop by indirectly measuring the impact force of the raindrop. The working range of the device is between 100