10 Nov 2021
10 Nov 2021
Status: a revised version of this preprint is currently under review for the journal HESS.

Influence of drop size distribution and kinetic energy in precipitation modelling for laboratory rainfall simulators

Harris Ramli1, Siti Aimi Nadia Mohd Yusoff1, Mastura Azmi1, Nuridah Sabtu1, and Muhd Azril Hezmi2 Harris Ramli et al.
  • 1School Of Civil Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Seberang Perai Selatan, Pulau Pinang, Malaysia
  • 2School of Civil Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia

Abstract. It is difficult to define the hydrologic and hydraulic characteristics of rain for research purposes, especially when trying to replicate natural rainfall using artificial rain on a small laboratory scale model. The aim of this paper was to use a drip-type rainfall simulator to design, build, calibrate, and run a simulated rainfall. Rainfall intensities of 40, 60 and 80 mm/h were used to represent heavy rainfall events of 1-hour duration. Flour pellet methods were used to obtain the drop size distribution of the simulated rainfall. The results show that the average drop size for all investigated rainfall intensities ranges from 3.0–3.4 mm. The median value of the drop size distribution or known as D50 of simulated rainfall for 40, 60 and 80 mm/h are 3.4, 3.6, and 3.7 mm, respectively. Due to the comparatively low drop height (1.5 m), the terminal velocities monitored were between 63–75 % (8.45–8.65 m/s), which is lower than the value for natural rainfall with more than 90 % for terminal velocities. This condition also reduces rainfall kinetic energy of 25.88–28.51 J/m2mm compared to natural rainfall. This phenomenon is relatively common in portable rainfall simulators, representing the best exchange between all relevant rainfall parameters obtained with the given simulator set-up. Since the rainfall can be controlled, the erratic and unpredictable changeability of natural rainfall is eliminated. Emanating from the findings, drip-types rainfall simulator produces rainfall characteristics almost similar to natural rainfall-like characteristic is the main target.

Harris Ramli et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2021-462', Rolf Hut, 07 Dec 2021
    • AC1: 'Reply on RC1', Mastura Azmi, 03 Feb 2022
  • RC2: 'Comment on hess-2021-462', Luca G. Lanza, 02 Jan 2022
    • AC2: 'Reply on RC2', Mastura Azmi, 03 Feb 2022

Harris Ramli et al.

Harris Ramli et al.


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Short summary
A rainfall simulator was designed, calibrated, and tested to produce heavy rainfall intensities like natural rainfall. Properties considered include appropriate density under constant head conditions that will influence the intensity of the raindrops based on the spacing of drop formers, uniformity of the application and the droplet size distribution. The results from this study show that kinetic energy and terminal velocity was dependent on particle size distribution.