Large numbers of numerical models are nowadays available for the description of physical and chemical processes affecting water flow and solute transport in soil vadose zone. This chapter explains basic principles of water flow and solute transport modelling in soil vadose (variably saturated) zone and some of the most important processes present in it. First part deals with water dynamics in the soil, that is, soil water content, pressure head, soil porosity, and water flow. Also, some of the measurement techniques used to estimate water dynamics in soil are explained. Water retention curve and soil hydraulic properties needed for modelling are briefly discussed with the explanation of basic (i.e. most commonly used) hydraulic relationship in soil (van Genuchten equation) and water flow (Richards equation) approaches. Second part includes solute transport description in vadose zone, including processes such as advection, diffusion, dispersion, and adsorption. Basic advection‐dispersion equation is explained and also the implementation of boundary and initial conditions in the numerical model. Preferential flow is shortly discussed with the basic principles behind its occurrence and modelling in the soil vadose zone. One real case one‐dimensional (1D) example of modelling with HYDRUS software is presented in which water flow and nitrate transport is simulated on the lysimeter study. Short overview of the most widely used numerical models for simulating vadose zone processes is also presented, whereas the final part is focused on chemical speciation modelling in relatively homogeneous soil solutions using visual MINTEQ interface.
Part of the book: Groundwater
The occurrence of drought periods which last for several months is becoming increasingly frequent, even in regions which have not encountered them before. Agricultural production is very sensitive to drought, and in areas where such conditions were rather unexpected, it is also unprepared for limited water management. As an example, in the area of the Biđ-Bosut field located in eastern Croatia, a significant change in the agricultural soil water regime is noticed during a long-term study (2003–2018). From 2003 to 2018, the groundwater level at 4 m below the soil surface showed a decreasing trend of 6–10 cm annually, while this negative trend was even more prominent from 2014 to 2018 (18–71 cm annually). Furthermore, water level in a groundwater aquifer at 15 m below the soil surface showed a decreasing trend of 26–77 cm during 2015–2018. In accordance with the obtained results, this study proposes certain agro-hydrotechnical strategies which can be used in agricultural production to alleviate the effects of drought period. Although these management strategies are primarily described on an eastern continental Croatia example, they can also be applied in all agricultural areas with similar agroecological conditions.
Part of the book: Drought