when the ring size was at least 15 cm. Gregory et al. (2005) concluded
that the test employing a constant headwith a double-ring infiltrometer
of 15 cm inner and 30 cm outer diameters would be suitable for sandy
soils generally found in North and Central Florida. Lai et al. (2010)
conducted a total of 7224 numerical simulations, which resulted in
a conclusion that inner ring diameters greater than 80 cmare needed
to obtain reliable in situ measurement of saturated hydraulic conductivity.
Fatehnia and Tawfiq (2014) by simulating 864 Double
Ring Infiltrometer tests and applyingM5′ model tree algorithm offered
an equation for hydraulic conductivity estimation from the steady infiltration
rate measurements that can be used for any ring size. They also
considered the effects of head of ponding, depth of the rings in the soil,
initial effective saturation of the soil, and soil type on steady infiltration
rate.
Depending on the soil texture and the initial soilwater condition, the
necessary measurement time of the test may be undesirably long. In
order to reduce the time consuming and tedious procedure of themeasurement,
continuous efforts have been previously done to automate
the test process. One of the earliest works was done by Constantz and
Murphy (1987). They utilized a single pressure transducer to develop
an automated Mariotte reservoir that enabled automatic recording of
water flow for constant head DRI test. Their infiltrometer was far from
being automated as their method required manual water level control
in both inner and outer rings. Their set-up was later modified by
Ankeny et al. (1988) for use as a “tension infiltrometer.” Tension