Soil Properties - Quantitative
Infiltration rate is a measure of how fast water enters the soil. This process affects surface runoff, soil erosion, and groundwater recharge. Infiltration rate is important when estimates of runoff are necessary. An infiltrometer is the device used to measure the rate of water infiltration into soil. However, infiltration cannot be measured with this method on very rocky or gravelly sites, steep slopes or areas that have dense root mats at the surface.
The most commonly used infiltrometers are single ring or double ring infiltrometers. They provide a relative indication of infiltration capacity under saturated conditions.
The single ring infiltrometer involves driving a single metal ring partially into the soil and filling it with water. Double ring infiltrometers in contrast require two rings (inner and outer), which creates a one dimensional flow of water from the inner ring. The inner ring is driven into the ground, while a second larger ring is located around the smaller one in order to help control the flow of water through the first ring. In both cases the rate at which the water moves into the soil is measured by recording how much water goes into the soil for a given time period. This rate becomes constant when the saturated infiltration rate for the particular soil has been reached. The rate at which water goes into the soil is related to the soil's hydraulic conductivity (or ease with which water can move through pore spaces or fractures). The difference between the single ring and double ring methods is that with single ring infiltrometers, water spreads laterally as well as vertically making the analysis more difficult.
Ring infiltrometers can be challenging to use since having to pound the infiltrometer into the ground disturbs the soil (i.e., soil compresion or cracking) which can alter the infiltration capacity measurement. Ground disturbance can also cause a poor connection between the ring wall and the soil, leading to a leakage of water and ultimately an overestimation of the infiltration rate.
In addition, there are many variations of this method and the size of the cylinder used in these infiltration devices can be a source of error.
As stated above, single-ring infiltrometers overestimate vertical infiltration rates because the flow of water beneath the cylinder is not only vertical, but spreads laterally as well. Double-ring infiltrometers minimize this error since the water level in the outer ring forces vertical infiltration of water in the inner ring.
Single-ring infiltrometers can be obtained from:
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