Delta flood risk analysis: case study from the Neretva River (Croatia)

Floods play an important role in deltas, particularly in their geomorphological and ecological processes. Current deltas are exposed to strong anthropogenic influences. In the Neretva River Delta (Croatia), which is located in the Mediterranean, numerous hydrotechnical facilities have been built for flood protection and flow regulation. The level of flood protection has significantly increased compared to natural conditions, because the main cause of flooding in this delta is fluvial flow, but there are still certain risks for material assets and the population. The hydrological regime of the Neretva River is strongly influenced by reservoirs and hydropower plants built upstream of the basin. This study presents a simulation of floods in the Neretva River Delta for various return periods (from 5 to 1000 years) to assess damages and risks. The extent of flooding is classified into three statistical levels: high, medium, and low probability. Floods in this area can cover approximately 110 km 2 with a low probability of flooding and material damage of approximately 250 million Euros. The average number of potential human victims would be 0.67 per year, and the potential average annual damage would be 11.63 million Euros, in the Donja Neretva according to the conditions of 2015. Climate change would increase the mentioned risks of floods, the potential number of victims and damage by 31 and 41%, respectively. Based on a multi-criteria analysis, protective measures including the construction of embankments and self-regulating gate were proposed. Their implementation would reduce the average annual potential number of victims and the average material damage by 70% and 83%, respectively. The results of this study should be used to identify critical areas and make decisions to improve the flood protection system in the delta area, as well as to improve water management in the entire basin, which is located in the territory of two countries Croatia and Bosnia and Herzegovina.