A Revisit of Rainfall Simulator as a Potential Tool for Hydrological Research

Abstract

Different means of hydrological data collection have developed and used. However, they are constraint in one way or other. This paper therefore revisited the rainfall simulator as potential tool for hydrological research. The research disclosed that there are three different types of rainfall simulators; drop former simulator, pressure nozzle simulator and hybrid simulator. It can further be classified as indoor model and outdoor. The research also showed that precipitation is the driving force in hydrological studies. Consequently, in the design of rainfall simulator, the following should be taken into consideration: nozzle spacing, pump size, nozzle size, nozzle type, nozzle spacing, plot size and pressure. Meanwhile, intensity, distribution uniformity, kinetic energy, rainfall drop size and rainfall terminal velocity should be noted in its evaluation. Factoring-in the aforementioned design considerations, data collection is made easy without necessarily waiting for the natural rainfall. Since the rainfall can be controlled, the erratic and unpredictable changeability of natural rainfall is eliminated. Emanating from the findings, pressurized rainfall simulator produces rainfall characteristics similar to natural rainfall, which is therefore recommended for laboratory use if natural rainfall-like characteristics is the main target.

Overview of the research gaps in the rainfall simulator study

“…(2002) and Ngasoh et al. (2021) stated that pressurized RS is better than unpressurized RS as it yields larger intensities, covers larger plot sizes, and is more portable.…”

“…Thus, unpressurized systems need a height of 9.1 m (Ricks et al., 2019), 7–10 m (Ngasoh et al., 2021), and 10 m (Blanquies et al., 2003) to reach terminal velocity and to represent natural rainfall, while pressurized RS that use nozzles and sprinkles require a shorter height as they have an initial velocity more than zero that allows portable and shorter RS to be sufficient in order to reach the terminal velocity (Blanquies et al., 2003).…”

“…According to Ngasoh et al. (2021), the terminal velocity should be reached before it reaches the ground from the right height to simulate natural rainfall conditions. The terminal velocity is the gravitational force that is cancelled by the drag force that is acting on the raindrop due to the viscosity of the air (Abudi et al., 2012).…”

“…(2019) stated that the drag force acting upon a droplet is equivalent to the square of the droplet velocity. The terminal velocity is measured by photographing the approximate time taken to pass consecutive points using an electronic device (Ngasoh et al., 2021). Abudi et al.…”

“…Since precipitation is the main driver for hydrological studies (Ngasoh et al., 2021), more studies should be conducted worldwide based on different geographical areas, latitudes, soil types, and climates. Beside, knowledge of test conditions (Iserloh et al., 2013) and rainfall properties (Mhaske et al., 2019) are vital to interpret and analyze results, although standardization of RS does not exist.…”