Environmental aspects and potential impacts of proposed water transfer scheme on sustainable water management in eastern Herzegovina

East Herzegovina is characterized by substantial water resources and abundant precipitation from October to May each year. As a result, the karst poljes of east Herzegovina are experiencing major, long-lasting floods during the rainy period and, conversely, insufficient recharge to the aquifer systems and rivers in the summer, often causing streams to completely dry out. Consequently, the karst poljes, which are the largest arable lands in the area, are rendered virtually useless during most of the year. To address this issue, the idea was born to build multi-purpose systems—the Trebišnjica Hydropower Scheme—in the so-called Lower Horizons and Upper Horizons, the primary and ultimate goal being the management of water resources in the area. The Lower Horizons scheme, which encompasses hydraulic structures, surface reservoirs, hydroelectric power plants, irrigation systems and drinking water supply facilities, was largely completed in the 1970s. The outstanding Upper Horizons project calls for comprehensive development of the water regime, including water resources management, social, environmental and energy components, as well as the transfer of water from the Neretva River Basin to the Trebišnjica River Basin (still under evaluation). Namely, interbasin transfer would reduce the discharges of the Neretva’s left tributaries: the Buna, the Bunica and the Bregava, but must not threaten minimal natural flows. The hydraulic model and preliminary environmental impact assessment indicate that there will be no significant adverse impacts; however, continuous monitoring of the effects during both construction and operation is mandatory.