Monitoring soil moisture dynamics using time-domain reflectometry (TDR)
1996
Mintesinot Behailu (Mekele University College (Ethiopia))
Time-domain reflectometry is becoming an important tool for monitoring the hydrodynamic characteristics of soils. In the present study, TDR was used to monitor the dynamic patterns of infiltration, redistribution and evaporation in a loamy sand soil. To obtain a comprehensive information regarding the dynamic patterns of these processes, TDR was complemented with tensiometry. From a column experiment conducted under a small rainfall simulator, it was found out that the evolution of moisture and potential dynamics during infiltration follow an exponential pattern. During redistribution process, two patterns were observed: an exponential pattern in the sorbing part and a linear pattern in the desorbing part of the column. Evaporation process investigated under two conditions (without and with a fan) showed two different patterns: a power form without a fan and a linear form with a fan. In an attempt to determine the water flux at the different probe depths, parkin et al (1995) model of predicting local infiltration was used. Resulted showed that, the slope from the linear regression of the cumulative storage over time provides an excellent estimate of the flux at the different probe depths. The TDR data was further used to trace back the simulated rainfall depth. Results revealed that, the increase in storage calculated from the TDR water content profiles excellently approximates (within 1.8-2 percent deviation) the applied rainfall depth. In an effort to trace back the rainfall depth from the TDR evaporation data, the cumulative evaporation between the end of infiltration (being the storage at the beginning of evaporation) and the end of evaporation (being the storage at the start of the infiltration) was calculated. Indeed, results showed that, for a given wetting-drying cycle, the rainfall depth was estimated within 5-5.6 percent deviation.
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