Mapping of soil moisture by time domain reflectometry and electrical resistivity tomography at Velika Gorica well field, Zagreb aquifer

Knowing the soil moisture distribution in the unsaturated zone can improve understanding the water flow through the unsaturated zone and thereby enable the calculation of aquifer recharge, which occurs through precipitation. One part of the Zagreb aquifer recharge occurs through infiltration from precipitation. In order to observe and model infiltration from precipitation through the unsaturated zone, the research polygon was constructed at the Velika Gorica well field, located in the southern part of the Zagreb aquifer, Croatia, where hourly measurements of electric conductivity (EC) and soil moisture content were carried out. EC and soil moisture data are measured by Time Domain Reflectometry (TDR) probes which are placed at different depths in the unsaturated zone. Furthermore, electrical resistivity tomography (ERT) measurements were conducted. Geophysical data, along with moisture and EC data from TDR probes, were used as input data for MoisturEC software, in order to obtain soil moisture distribution along a 2D profile. MoisturEC program offers three options for translating EC data to moisture content data which are all tested in this research. We obtained eight moisture content distributions along the observed profile and concluded that MoisturEC provides reasonable results with input data from geophysical measurements and TDR probe measurements. Soil moisture distribution in the unsaturated zone represents the initial conditions for further unsaturated flow modeling. Understanding the flow in the unsaturated zone enables the quantification of effective infiltration and can improve groundwater management. Poznavanje raspodjele vlažnosti u nesaturiranoj zoni može doprinijeti razumijevanju toka vode kroz nesaturiranu zonu a time i omogućiti izračun prihranjivanja vodonosnika putem oborine. Jedan dio prihranjivanja zagrebačkog vodonosnika čini oborina. U cilju promatranja i modeliranja infiltracije oborine kroz nesaturiranu zonu izgrađen je znanstveno-istraživački poligon na vodocrpilištu Velika Gorica, u južnom dijelu zagrebačkog vodonosnika, u kojem postoje satna mjerenja električne vodljivosti i sadržaja vode u tlu. Električna vodljivost i vlažnost mjere se TDR (eng. Time Domain Reflectometry) sondama koje su postavljene na različitim dubinama u nesaturiranoj zoni. Nadalje, provedena su i geofizička mjerenja gdje je korištena metoda električne tomografije. Podaci dobiveni geofizičkim istraživanjem te podaci o električnoj vodljivosti i vlažnosti dobi