Infiltration is the process of flow of water from the soil surface into the ground. Further the movement of water into subsurface soil is called percolation. Infiltration followed by percolation recharge the groundwater which eventually reaches the streamflow. The rate at which the water enters into soil is called infiltration rate. The measurement of infiltration rate is important in problems including runoff, irrigation, seepage, soil erosion, leaching, drainage and various others. Hence the measurement of the infiltration rate is of utmost importance .The infiltration can be measured by flooding type infiltrometers. Flooding type infiltrometer experiment is an in situ experiment carried out using infiltrometers to observe the rate at which water enters into soil at various intervals of time. There are two types of infiltrometer a) simple or tube type infiltrometer and b) double-ring infiltrometer.

The tube type infiltrometer is commonly called a “single-ring infiltrometer”.Single ring infiltrometer is a metallic ring driven into ground up to a certain depth and filled with water till the marked level. The reduction in water level and change in volume of water is noted down. The reduced water level is brought to initial level by adding additional water in order to measure the rate of change of water depth with time. The experiment is continued till the infiltration reaches a steady state condition.Although the double ring infiltrometer is used widely to estimate the infiltration rate, the single ring infiltrometer is also well accepted by many hydrologists. One major drawback of a single ring is the unfiltered water spreads outwards from the tube. The total volume of water infiltrated into the soil in a given period of time is called accumulated/ cumulative infiltration . The unit is mm or cm. The average infiltration rate is the fraction of accumulated infiltration depth divided by the total time of infiltration. And the unit is cm/hr, mm/min, mm/hr.

Horton’s equation is a commonly used empirical equation to calculate the infiltration capacity of soil.

k = a Horton’s decay coefficient constant representing the rate of decrease in f capacity. fc = a final steady state infiltration capacity
t=tc
fo = the initial infiltration capacity at t=0