Modeling seasonal water flow dynamics in unsaturated zone of hydromorphic soil

Podzemne vode uključuju vodu smještenu u dubljim slojevima tla u uvjetima potpune saturacije. Tok podzemne vode podijeljen je na strujanje u saturiranim i nesaturiranim uvjetima. Tok u nesaturiranoj sredini prvenstveno je vertikalan, a tok u saturiranoj sredini prvenstveno je horizontalan. Modeli toka podzemnih voda opisuju tok podzemnih voda i transport tvari pomoću matematičkih jednadžbi temeljenih na pojednostavljenim pretpostavkama. U nesaturiranoj zoni tla modeliranje je složenije zbog stalne promjene vlažnosti tla uslijed oborina kao i varijacija razine podzemne vode. Određivanje vodnog režima nesaturiranih horizonata tla uzimajući u obzir sezonske razlike u razinama podzemnih voda na odabranim lokacijama provedeno je pomoću numeričkog modela HYDRUS-1D. Numerički model ispitan je pomoću podataka dobivenih s lizimetra na pet lokacija u polju Biđ (istočna Hrvatska). Model je validiran na temelju isteka iz samih lizimetra s visokom razinom pouzdanosti (R2 = 0,87 - 0,96). Hidropedološka svojstva tla određena su na pet lokacija kako bi se mogao odrediti režim vode tla nesaturirane zone s obzirom na sezonske varijacije razine podzemnih voda mjerenih u blizini svake odabrane lokacije. Rezultati su pokazali velike varijacije u razinama podzemnih voda na svakoj lokaciji, što je bio glavni uzrok oscilacija relativne količine vode i vodnog potencijala u višim slojevima tla. Niska količina oborina u promatranoj godini rezultirala je još većim utjecajem podzemnih voda na pokusnom području. Navedeni rezultati ukazuju na važnost resursa podzemnih voda u poljoprivrednoj proizvodnji s obzirom na njihov značajan utjecaj na površinski horizont tla, a posebno kada su potrebni sustavi navodnjavanja.Groundwater includes water located in deeper soil layers characterized by a complete saturation. The groundwater flow is divided to flow in saturated conditions and flow in unsaturated conditions. Water flow in unsaturated medium is primarily vertical and water flow in the saturated medium is primarily horizontal. Water flow models describe the groundwater flow and solute transport using mathematical equations based on certain simplified assumptions. In unsaturated soil zone modeling is more complex due to the constant change in soil moisture as a result of precipitation and groundwater level variations. Determining the water regime of the unsaturated soil zone, while taking into account the seasonal variations of groundwater levels at selected locations, were carried out using the HYDRUS-1D numerical model. The numerical model was tested using the data obtained from the lysimeters at five locations in the Biđ field (eastern Croatia). The model was successfully validated with a high level of confidence on lysimeter outflow (R2 = 0,87 – 0,96). Hydropedological soil properties were determined at five locations to determine soil water regime of the unsaturated soil zone considering seasonal variations of groundwater levels measured at the proximity of each location. Results show different groundwater levels at every location, which had a major influence on water content and pressure head oscillations in the upper soil layers. The low amount of precipitation in the observed year resulted in even larger effect of groundwater levels at the experimental sites. Results highlight the importance of groundwater resources in agricultural production because of their significant influence on soil surface layer, especially when irrigation practices are needed