Abstract
This paper presents a model of flow and solute transport of intermittent catchments in arid and semi-arid regions, highlighting challenges caused by the complex interactions between subsurface and surface flows. A case study is used for the application of the integrated MIKE SHE model to investigate temporal and spatial dynamics of water and salinity in a small ephemeral catchment in southwestern Victoria, Australia. MIKE SHE was successfully calibrated and validated against experimental data of streamflow, groundwater levels, and salt discharged from the catchment. Projections of climatic conditions, adopting Representative Concentration Pathways (RCPs) 4.5, 6.0, and 8.5, were used to infer how salinity discharge and concentrations might be affected across a range of greenhouse gas emission scenarios with different severity. The calibration of the water fluxes was solely based on parameters associated with the model of evapotranspiration, with other parameters selected from field observations and literature. The calibrated parameters for the salt transport were the longitudinal and lateral dispersivities. The calibration and validation of streamflow series led to Index of Agreement (IoA) of 0.92 and 0.8 respectively, while the simulation of groundwater levels was more challenging (IoA ranging from 0.22 to 0.89). Parameter equifinality was observed, with different parameter sets achieving a good fit of streamflow and groundwater levels, although leading to differing spatial patterns of evapotranspiration rates. Calibration and validation of the discharge concentrations appeared more difficult (IoA of 0.35 for calibration and 0.44 for validation) as they are affected by errors in the simulated flow. Climate projections RCP 8.5 suggested a reduction of salt discharge with consequent increased concentrations within the catchment. The study showed the ability of MIKE SHE to be successfully applied to intermittent dry catchments to possibly support water and land management.
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