International Journal of Engineering, Sciences and Technologies www.scienceresearchlibrary.com International Journal of Engineering, Sciences and Technologies Published online 20 September 2014 (http://www.scienceresearchlibrary.com) Vol. 0 1 , No. 0 1 , pp. 1 - 4 Research Article Open Access Physical Simulation of Rainfall-Runoff System by a Hydrology Bench Md. Nurul Kadir 1 , Taznin Naher 2 and Dr. M. Hassanuzzaman Khan 3 1 Research Associate, IWFM, BUET, Dhaka-1000, Bangladesh 2 Research Fellow, IWFM, BUET, Dhaka-1000, Bangladesh 3 Professor, Department of IWM, BAU Mymensingh-2202, Bangladesh Received: 1 September 2014 / Accepted: 17 September 2014 ⓒ Science Research Library Abstract This study was conducted to simulate the rainfall-runoff system by a hydrology bench in a hydraulic laboratory. The hydrology bench consisted of a 210.8 cm long, 108.0 cm wide and 16.5 cm deep metallic tray with an overhead sprinkling system. A river network was created on the soil bed in the tray. Rainfall on the tray was simulated by supplying water by a pump through the sprinkling nozzles. There were two outlets, one to drain surface runoff and the other the subsurface runoff. Surface runoff hydrographs were developed for different rainfall durations on two different surface conditions, such as simple soil bed and gravel spread bed. The results were analyzed to verify the theories used in analysis of hydrographs, as available in relevant text books. Uniformity of rainfall distribution over the catchment was also analyzed. The results showed that the hydrology bench could simulate rainfall-runoff system quite satisfactorily. The simulation was better on the soil bed than the gravel spread bed. The rainfall distribution was not very satisfactory. However, the analysis of hydrographs showed that theories used in literature were in good agreement with the practical findings. Keywords: Simulation, Rainfall-Runoff, Hydrograph, Hydrology bench. *Corresponding author: mnkseum@gmail.com, tnsabia@gmail.com, mhkhan@yahoo.com Introduction Rainfall duration and intensity influence the rate and volume of runoff. The rainfall-runoff simulation is the process of representing the natural rainfall-runoff system by means of an artificial simulator. A simulator may be mathematical or physical. A physical rainfall-runoff simulator consists of a metal tank that supports spray head assembly. The unit may be placed directly on the ground for field studies or used with its accessory tray for laboratory experiment. In use, water is pumped from the holding tank via a control valve to the spray nozzle to produce artificial rainfall. In a rainfall simulator, specially designed nozzles produce raindrops of various sizes falling from a desired height and are capable of producing various intensities of rainfall. The metal tank acting as a catchment can generate runoff which is also influenced by the surface condition maintained in the tank. So, these simulators can be used to study the effects of intensity and duration of rainfall and catchment conditions on the volume and rate of runoff generation. In this work, a hydrology bench was used to simulate rainfall-runoff system in the laboratory. The objective of the study was to develop and analyze runoff hydrographs for different rainfall durations on two different surface conditions of the simulator catchment. Materials and methods Hydrology bench The hydrology bench consisted of a sand/soil filled metallic tray to act as a micro catchment and an over-head sprinkler device to produce rainfall on the catchment. The Metallic tray was 211.0 cm long, 108.0 cm wide and 16.5 cm deep, filled layer by layer with different textures of dry sieved soil. The top and bottom layer consisted fine soil and very coarse material to represent natural