THE DESIGN AND CONSTRUCTION OF NON-PRESSURIZED RAINFALL SIMULATOR FOR WATER BUDGET ESTIMATION (RUN OF, INFILTRATION AND TRANSPIRATION) IN MAUTECH FARM IS THE CASE STUDY

ABSTRACT 
Rainfall simulator is an important instrument for producing artificial rainfall for the determination of soil loss from a catchment over a given period of time. The instrument is rarely available in most Nigeria Universities for practical demonstration for students and research in Soil and Water Conservation Engineering. This is due to high cost of the rainfall simulator and materials that are commonly used for the construction of rainfall simulator are not readily available or expensive in developing countries. In this study, a pressurized rainfall simulator was designed and constructed using the locally available materials mainly PVC pipe, shower rose and a pump for supplying water to the simulator for its operation. The main-pipe receives water from the pump and supplies it to the laterals. The laterals supply water to the distribution pipe which passes it to the shower rose. One hundred shower roses on ten laterals spray water to the ground surface through 2 mm openings. The simulator was 3 by 3 m and all the components are detachable for portability. The simulator rests on an adjustable frame which could be varied from 1 to 2 m height. The coefficient of uniformity and drop velocity from the simulator during the performance test were 84.4 % and 8.16 m/s, respectively. The results of coefficient of uniformity (CU) and drop velocity (DV) were within the range because the recommended minimum values of CU and DV were 81 % and 8.06 m/s, respectively. The intensity of water dropping from the simulator depends on the inflow rate of water which could be regulated by the control tap fixed to the inlet main-pipe. 

CHAPTER ONE: INTRODUCTION 
1.1 BACKGROUND 
Top soil is very important for agricultural purpose but it is usually washed away in the tropical countries like Nigeria by erosion due to heavy rainfall with high intensity which is common in tropics. The consequence of soil erosion is degradation of arable land thereby reducing the size of the productive land for agriculture (Pimentel, 2006). The potential ability of rainfall to cause soil erosion is termed erosivity while the vulnerability of soil to detachment by the impact of rainfall and transportation of the soil particles by the runoff is called erodibility (Schwab, et al., 1993 as cited by Yusuf et al., 2016) 

Man has no control over the natural rainfall properties such as rainfall intensity, drop size and duration of rainfall. 

Rainfall simulator is a useful tool which can be regulated for creating artificial rainfall that is synonymous to natural rainfall pattern in order to study the impact of rainfall on soil surface and how it causes erosion. Simulators are not readily available in Nigeria for research and not available in most Nigerian Universities for students to use for practical. There is need for a simple rainfall simulator which should be designed and constructed using the locally available materials for research and practical by students. Rainfall simulator for field experiment must be portable, withstand wear and tear, the components must be easily assembled and disassembled to eradicate theft, vandalism, ease of transportation, simple design and must produce rainfall similar to natural rainfall (Loch et al.,2001). 

1.2 RAINFALL SIMULATORS 
There are two main types of rainfall simulator which are; drop–forming simulator also known as non–pressurized simulators and pressurized nozzle simulators (Thomas et al., 1987 as cited by Yusuf et al., 2016). Drop-forming simulator is not usually portable and required high elevation between 10 and 12 m to attain the terminal velocity (Grierson et al., 1987 as cited by Wilson et al., 2014). Bowyer-Bower and Burt (1989) as cited by Yusuf et al. (2016) also pointed out that pressurized nozzle rainfall simulator (spray type) uses more water (because of wide area receiving water) than drop–forming type simulator. The pressurized nozzle simulators are suitable for many areas and the intensity could be varied (Grierson and Oades, 1987 as cited by Yusuf et al., 2016). 

The intensity of water from the nozzle varies with orifice diameter, hydraulic pressure on the nozzle and the spacing of the nozzle. Fernandez-Galvez et al. (2008) used a simulator that have a wide range of intensities from 1 –120 mm/hr. The operating pressures for the pressurized nozzle simulators usually produced by a pump are from 34 to 3400 kPa to produce the flow rates between 13.3 and 132 L/min (Junior and Siqueira, 2011). Bubenzer (1987) as cited by Yusuf et al. (2016) found that 41 kPa produced drop size and intensity similar to natural rainfall. The simplest form of sprays that may be suitable for many applications is a spray from watering can or the rose connected to a pressurized hose. Drop size distribution depends on many characteristics especially rainfall intensity. The drop size varies with intensity ranging from 1 to 7 mm. The median drop size distribution for high intensity storm is 2.25 mm (Laws and Parsons, 1993 as cited by Wilson et al., 2014). Rainfall from rainfall simulator should drop or fall at its terminal velocity, if they are to have the same level of energy as natural drops of the same size. Terminal velocity is defined as the velocity at which objects fall without further acceleration due to gravity (Raghunath, 2006). In other words, for a free falling sphere at terminal velocity, the gravitational force will be equal to the dynamic force on the falling sphere. Wischmeier and Smith (1978) as cited by Yusuf et al. (2016) found that rainfall intensity is highly correlated to kinetic energy of rainfall and kinetic energy is the most important factor influencing the ability of rainfall to cause erosion. The objectives of this study were to: (i) design and construct a simple rainfall simulator using the locally available materials and (ii) determine the uniformity coefficient of rainfall simulator.. 

1.3 RESEARCH OBJECTIVES 
The primary purpose of this research is to incorporate the use of a non pressurized rainfall simulator water budget estimation (run of, infiltration and transpiration) in MAUTECH farm. The objectives of each phase are detailed below: 

1. Design a rainfall simulator and electrical control system that will provide uniform coverage and produce consistent, repeatable rainfall on the test plot. 

2. Develop testing protocols to ensure consistent, repeatable conditions for the test plot 

(i.e. plot preparation, soil type, compaction, moisture content). 

3. Develop testing protocols to calibrate the rainfall simulator and ensure that the system is satisfying all criteria to produce uniform raindrop coverage that mimics natural rainfall. Evaluate the performance of the rainfall simulator and its ability to simulate natural rainfall, while producing repeatable conditions through calibration of the rainfall simulator and validation of the test results.

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Item Type: Project Material  |  Attribute: 52 pages  |  Chapters: 1-5
Format: MS Word  |  Price: N3,000  |  Delivery: Within 30Mins.
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