Infiltrometer
Encyclopedia
Infiltrometer is a device used to measure the rate of water infiltration
Infiltration (hydrology)
Infiltration is the process by which water on the ground surface enters the soil. Infiltration rate in soil science is a measure of the rate at which soil is able to absorb rainfall or irrigation. It is measured in inches per hour or millimeters per hour. The rate decreases as the soil becomes...

 into soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...

 or other porous media. Commonly used infiltrometers are single ring or double ring infiltrometer, and also disc permeameter
Disc permeameter
The disc permeameter is a field instrument used for measuring water infiltration in the soil, which is characterized by in situ saturated and unsaturated soil hydraulic properties...

.

The single ring involves driving a ring into the soil and supplying water in the ring either at constant head
Hydraulic head
Hydraulic head or piezometric head is a specific measurement of water pressure above a geodetic datum. It is usually measured as a water surface elevation, expressed in units of length, at the entrance of a piezometer...

 or falling head condition. Constant head refers to condition where the amount of water in the ring is always held constant. Because infiltration capacity is the maximum infiltration rate, and if infiltration rate exceeds the infiltration capacity, runoff will be the consequence, therefore maintaining constant head means the rate of water supplied corresponds to the infiltration capacity. The supplying of water is done with a Mariotte's bottle
Mariotte's bottle
Mariotte’s bottle is a device that delivers a constant rate of flow from closed bottles or tanks. It is named after French physicist Edme Mariotte . A picture of a bottle with a gas inlet is shown in the works of Mariotte, but this construction was made to show the effect of outside pressure on...

. Falling head refers to condition where water is supplied in the ring, and the water is allowed to drop with time. The operator records how much water goes into the soil for a given time period. The rate of which water goes into the soil is related to the soil's hydraulic conductivity
Hydraulic conductivity
Hydraulic conductivity, symbolically represented as K, is a property of vascular plants, soil or rock, that describes the ease with which water can move through pore spaces or fractures. It depends on the intrinsic permeability of the material and on the degree of saturation...

.
Double ring infiltrometer requires two rings: an inner and outer ring. The purpose is to create a one dimensional flow of water from the inner ring, as the analysis of data is simplified. If water is flowing in one-dimension at steady state condition, and a unit gradient is present in the underlying soil, the infiltration rate is approximately equal to the saturated hydraulic conductivity.
An inner ring is driven into the ground, and a second bigger ring around that to help control the flow of water through the first ring. Water is supplied either with a constant or falling head condition, and the operator records how much water infiltrates from the inner ring into the soil over a given time period.

There are three main problems related to the use of infiltrometers:
1. The pounding of the infiltrometer into the ground deforms the soil causing cracks and increasing the measured infiltration capacity.
2. Natural rainfall reaches terminal velocity. Also natural droplet sizes differ with different types of storms. Pouring water from a measuring cup however loses this momentum and variance.
3. With single ring infiltrometers, water spreads laterally as well as vertically and the analysis is more difficult.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK