Soil water content estimation from point scale to plot scale

Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Civil Engineering, Turkey

Approval Date: 2018




Estimating soil moisture is crucial for understanding vadose zone and surface hydrology dynamics. In this study, soil moisture measurement is investigated by using a range of techniques spanning different spatial scales in a test basin in the south of Turkey. A cosmic ray sensor soil moisture probe (CRS) and a water content reflectometer (CS-616) have been installed for retrieving volumetric soil moisture data continuously. Lab analyses have been performed for calibrating the installed instruments and to obtain the pore water electrical conductivity range in the study area. The average pore water conductivity value is obtained as 933 μS/cm, and it is observed that the variation of the pore water conductivity is not directly related to clay content. Electrical resistivity imaging (ERI) was used to map water content variation in a 2-D shallow unsaturated zone within the footprint of the CRS. Schlumberger and WennerAlpha electrode array with 0.50 m electrode spacing were used along 19.5 m resistivity profiles in the field surveys. Soil moisture measurements were done with CS-616 at these profile locations, concurrently. Archie’s Law has been used to reveal the relationship between soil moisture and resistivity. Archie’s cementation index (m) and saturation index (n) were calculated for the footprint as 1.57 and 1.152, respectively. This study reveals that ERI has limited sensitivity to the moisture content in the study area, whereas the CRS shows good agreement with the values obtained from the installed CS-616 at point-scale, and rainfall amount observed at a nearby meteorological station.