A multi-model approach to the simulation of large scale karst flows

SummaryThe possible effects of water transfer through a tunnel from Fatničko Polje to Bileća Reservoir on the hydrologic regime of the Bregava River located in Eastern Herzegovina, in an area characterised by a predominantly karstic terrain, are studied. Three different simulation models of the area were developed and their predictions compared under a range of current and future hydrological and operational management conditions. These are based on a range of modelling approaches from a simplified conceptual approach to a quasi-physically based one. Despite the large complexity of the natural system, the models gave good fits to existing flow data with the most simplified model providing the closest agreement to historical flows. Calibrated models were used to study the possible effects of the intervention under a range of operational scenarios and identify the sources of the associated uncertainties. The results of the work suggest that the system of tunnels in question has a favourable effect in reducing flood hazard in the area, thus liberating scarce land resources for agriculture, and in reducing flows in the Bregava River (especially high flows). It is also suggested that a significant reduction in the uncertainty of modelling the karstic environment can be achieved by an appropriate, complementary combination of modelling approaches viewed as a multi-model ensemble.