TDR application for automated water level measurement from Mariotte reservoirs in tension disc infiltrometers

Abstract

This paper describes the use of an automated method of measuring water level changes in Mariotte-type reservoirs via time domain reflectometry (TDR) and demonstrates its field application for measurements of soil hydraulic properties. The method is based on the assumption that the travel time of a TDR pulse propagating along a transmission line immersed in an air-water medium is the summation of the pulse travel times in the air and water phases. A TDR cable tester generates a pulse that propagates through a three-rod probe traversing the centre of the Mariotte reservoir from top to bottom. The reflection of the pulse is automatically transferred to a computer for waveform analysis with the water level being a simple function of probe length and the air, water, and air-water medium dielectric constants as measured by the cable tester. Water level measurements obtained with the TDR technique showed close agreement with those obtained using visual and pressure transducer procedures. The application of this TDR method as an alternative to more traditional methods was demonstrated in a field experiment using a tension disc infiltrometer. The TDR approach allows for automated water level measurements and is simple, accurate and easy to implement. Moreover, it allows for simultaneous TDR measurements of both water flow and volumetric water content of soil below the infiltrometer disc.

Dynamics of soil hydraulic properties during fallow as affected by tillage

“…The field soil hydraulic properties were characterised at each observation point using a 1 modified Perroux and White (1988) tension disc infiltrometer with a base radius of 125 mm 2 as described by Moret et al (2004) for structured soils and Moret and Arrúe (2005) for freshly 3 tilled soils. Infiltration measurements were taken on areas cleared of surface crust, large clods 4 and crop residue and brushed smooth.…”

“…On average, the minimum time to reach a steady-state condition varied from 10 to 12 45 minutes for the 0 to -14 cm of water pressure head range. Flow readings were 13 automatically recorded every 30 seconds from the drop in water level of the water supply 14 reservoir of the infiltrometer, by using a three-rod TDR probe vertically placed in the center 15 of the water reservoir and connected to a TDR pulser (Tektronix 1502C metallic Time 16 Domain Reflectometer) according to the procedure described by Moret et al (2004). 17 The soil hydraulic conductivity, K, at the different water pressure heads (K 14 , K 4 , K 1 , and 18 K 0 ) and the matric flux potential were calculated from cumulative infiltration using the 19 multiple-head method (Ankeny, 1992).…”

New automatic minidisk infiltrometer: design and testing

“…However the device seems to be overcomplicated and not suitable for use in the field. Moret et al (2004) suggested water level registration using a time domain reflectometry probe placed in the reservoir tube. Another method proposed by Jara et al (2012) or Rodný et al (2013) is based on sequential imaging of water level in the infiltrometer's reservoir using an automatic camera or a smart phone's digital camera.…”

An automated microinfiltrometer to measure small-scale soil water infiltration properties

“…Various designs of automated infiltrometers have been developed, with the simplest using a pressure transducer to measure the rate of water loss from an infiltrating falling head (Arriaga et al, 2010). Steady-state tension infiltrometers have also been developed that measure water infiltration directly with microflowmeters (Moret-Fernandez et al, 2012), indirectly from pressure transducers located in the air and water of a Mariotte bottle (Casey and Derby, 2002;Madsen and Chandler, 2007;Prieksat et al, 1992), or from the height of the water column in the infiltrometer measured using TDR (Moret et al, 2004) or infrared sensors (Milla and Kish, 2006). Very sophisticated infiltrometers that change hydraulic head (Moret-Fernandez et al, 2012) and refill automatically (Castiglione et al, 2005) have also been developed.…”