Hydrologic modelling of a complex hydrogeologic basin: Evrotas River Basin

Abstract

Climate change is expected to affect mostly water resources in arid and semi-arid areas, imposing in this way significant constraints in satisfying water demands in these regions. Under these conditions, water resources management should focus in increasing the efficiency of water uses by minimizing water losses and improving on the water balance accounting of the watersheds. Evrotas River Basin is a typical case of a water resource that has been under intense human pressure due to extensive water abstractions. Pumping from numerous wells (approximately 3000 private wells) and surface water abstractions impose significant uncertainty in water balance estimation and a new approach was developed to constrain the system and improve on the water balance assessment. The ETD (Enhanced Trickle Down model), a physically-based watershed model was coupled to a karstic model and were used to simulate the hydrologic response of the watershed. Ten years of data were used to simulate the hydrologic regime of the watershed. Losses from the karst due to evapotranspiration and infiltration to the deeper aquifer were estimated to be 45% of its annual volume. Karst is recharged annually by a water volume of 306Mm³ and only 24% (75Mm³) recharges the river as karst baseflow. The annual rainfall volume (for the non-karstic area of the watershed) was estimated to be 629Mm³, the evapotranspiration was 655Mm³, stream discharge 152Mm³ and stream abstraction and irrigation were 77Mm³. On the average, the amount of irrigation (77Mm³) corresponded to 900 mm (per year for agricultural areas) which is almost twice the recommended irrigation levels. The modelling approach presented in this work can be used to constrain the uncertainty in the hydrologic budget of basins with complex hydrogeomorphology.