CHAPTER ONE INTRODUCTION 1.1 BACKGROUND OF THE STUDY
A rainfall simulator allows the generating of rainfall with a known intensity and duration which can always be determine by a well calibrated rain gauge over an area in a collaborated manner, making it possible to quantify or measure.
In this way, rainfall simulator have widely contributed to the understanding of rainfall, rainfall determination practices can be carried out. There are different between natural and simulated rainfall (artificial rainfall).it is possible to find out the different between the two and three characteristic.
The simulator consists of a square frame, having different dimensions of the top and another at the base with respect to the function and characteristic properties of the simulator. The rainfall simulator supported by four metal pillars, valves are used at the inlet and the out-let of the system, the inlet valve controlled the pressure the rain that will be discharged while the outlet valve in or securing .
The uniformity of the range fall can be obtained from the outlet distributing channels placated at different positions on the simulator.
1.2 RAINFALL
Rainfall is defined as the amount of water falling in form of rain, snow, hail or sheet in a specified area and time interval. It can also be defined as the quantity of water, expressed in millimeter precipitated as rain, snow, hail or sheet within a given time and are usually given as a hypothetical depth of coverage.
Rain is liquid in the form of droplets that have condensed from atmosphere water vapour in the precipitate (becomes heavy enough to fall under gravity). Rain is a major component of the water cycles and is responsible for deposition most of the freshwater on earth. It provides suitable conditions for many types of ecosystems, as well as water for hydroelectric power plants and crop irrigation.
The major causes of rain production is moisture moving along three dimensional zones of temperature and moisture contrast known as weather points. If enough moisture and upward motion is present, precipitation falls from convective clouds (those with strong upward vertical motion) such as cumulonimbus (thunder clouds) which can organize into narrow rain bands. In mountainous areas, heavy precipitation is possible where upslope flow is maximize within windward sides of the terrain elevation which forces most air to condense and fall out as rainfall along the sides of mountains. On the leeward side of the mountains desert climates can exist due to the dry air caused by down slope flow which causes heating and drying of the air mass. The movement of the moisture through, or intertropical convergence zone brings rainy seasons to savannah climates.
Rainfall is measured using rain gunges. Rainfall amount can be estimated by weather rador.
Rain is also known or suspected under planets where it may be composed of methane, neon, sulfinic acid or even iron rather than water.