Impacts of vegetation cover on surface-groundwater flows and solute interactions in a semi-arid saline floodplain: a case study of the Lower Murray River, Australia

Despite many studies on floodplain vegetation, there is limited quantitative understanding of the role of vegetation in surface water (SW) and groundwater (GW) interactions through processes such as evapotranspiration. Moreover, most of the investigations that have been undertaken on SW-GW interactions consider 1D or 2D model set-ups. In addition, most of the modelling studies in this research area have only included water but not solute transport. This paper presents the results of a study on the potential impacts of vegetation cover on the interaction of a river and a saline semi-arid floodplain aquifer using a 3D physically-based fully integrated numerical model. In this regard the following three scenarios were defined: current vegetation cover (calibration model), deep-rooted vegetation cover and shallow-rooted vegetation cover. Clark's Floodplain, located on the Lower Murray River in South Australia was selected as the study site. The results show that deep-rooted vegetation cover may maintain relatively deeper groundwater levels and a less saline floodplain aquifer. Also, it is shown that in the shallow-rooted scenario, most of the ET component belongs to the evaporation process due to shallower groundwater. On the other hand, the deep-rooted model includes groundwater uptake largely via a transpiration process, and consequently keeps the groundwater levels below the evaporation depth. Overall, in semi-arid areas, the vegetation cover type can have significant impacts on the flow and solute interaction dynamics of a river and a floodplain aquifer due to the influence of ET as a dominant hydrological driver.