ABSTRACT
The primary objective of this research was to develop and evaluate an acceptable instrument for field measurement of infiltration. Many situations arise in civil engineering, irrigation and hydrology where it is desirable to evaluate infiltration of water into the soil under either ponded or rainfall conditions. An example is in the prediction of the rate of surface runoff. During a given storm rainfall intensities in excess of infiltration rates give rise to surface runoff. Since a large percentage of the rainfall infiltrates into the soil, the accuracy with which the surface runoff can be predicted is therefore dependent on the evaluation of infiltration. Infiltration is the movement of water through the soil surface and into the soil and is distinguished from percolation, which is the movement of water through the soil profile. It is the source of soil moisture needed to sustain the growth of vegetation and of the groundwater supplies of wells, springs, and streams. Through infiltration the soil surface divides rainfall into overland flow, and soil moisture and groundwater. Some of the sources of water are: rain, dew, frost and irrigation.The maximum rate at which water will enter the soil in a given coalition is known as the infiltration capacity. The infiltration rate is the rate at which water enters the soil during a rainstorm, and it must equal the infiltration capacity, or the rainfall rata, whichever is least. It has the dimensions of volume per unit time per unit of area. Infiltration rates may be determined experimentally by measuring the surface runoff from a small test plot subject to either natural or simulated rainfall. The most important items influencing rate of infiltration have to do with the physical characteristics of the soil and the cover on the soil surface, but such other factors such as soil moisture, rainfall intensity, temperature are also involved. A comprehensive review of literature regarding the factors affecting infiltration and the methods of measurement is included in this thesis. Infiltration measurements have been conducted by different methods in the past by observing runoff from natural or artificial rainfall or by observing the rate of fall of ponded water. The most suitable method of measuring infiltration will depend upon the intended application, the equipment, and other resources available. Since there is no single accepted method for measuring infiltration rate, it is of particular interest therefore, to derive a standard method of infiltration measurement in the Local Soil, However, to find a simple but reliable infiltration measurement many existing methods were examined and due to various reasons stated under chapter II of this thesis two methods were investigated and from the results obtained, it was determined that the buffer cylinder infiltrometer method was the most reliable, and also give the highest degree of accuracy.