Coupling surface and groundwater processes for water resources simulation in irrigated alluvial basins

Understanding the interaction between soil, vegetation and atmosphere processes and groundwater dynamics is of paramount importance in water resources planning and management in many practical applications. This is the case, for example, of the most important agricultural and industrial area in Italy, the Padana Plain, where intensive exploitation of groundwater for domestic and industrial supply coexists with massive diversions from surface water bodies, providing abundant irrigation to one of the most productive agricultural districts in Europe. Hydrological models of such complex systems need to include a number of components and should therefore seek a balance between capturing all relevant processes and maintaining data requirement and computing time at an affordable level. Water transfer through the unsaturated zone is a key hydrological process, at the interface between surface and ground water. The paper focuses on the analysis of the modelling approaches that are generally used to describe the soil water dynamics in hydrological models of water resources systems. A physically based approach, using numerical solutions of Richards equation, and two conceptual models, based on reservoirs cascade schemes, are compared. The analysis is part of a comprehensive modelling study of water resources in a 700 km2 irrigation district in northern Italy. Simulations are carried out using ten years of rainfall data and a number of soil profiles that are representative of the pedological characteristics of the study area. Based on the analysis of results, showing significant differences in the simulated patterns of output variables, a number of remarks are drawn.