Slovenian Water Agency, in cooperation with the Municipality of Kostanjevica na Krki, organized an Online Stakeholder Workshop on scenarios for flood risk reduction in the pilot area Kostanjevica na Krki on 2nd of October 2020. More than 30 attendees from 15 institutions participated at the meeting which was the 2nd official stakeholder meeting of the Danube Floodplain project.

During implementation of the Danube Floodplain project, several scenarios for the purpose of flood risk reduction were developed:

Scenario 1 - combination of a corridor enabling floodplain activation, and measures to increase water conductivity in the river bed through Kostanjevica, thus lowering water levels within the settlement.

Scenario 2 – a wider combination of a corridor enabling floodplain activation, and measures to increase water conductivity in the river bed through Kostanjevica, thus lowering water levels within the settlement.

Based on the results of the hydraulic simulations of the scenarios, scenarios 1 and 2 have no significant impact on the flood hazard in Kostanjevica.

Scenario 3 – here we tried to combine several approaches to get a confirmation, if quite extensive measures can assure any result in lowering water levels within the settlement.

Scenario 3 includes construction of the bypass channel, construction of levees, elevation of the road between the floodplain and the settlement, construction of dams (for inflow from the Krka river to the floodplain and outflow from the floodplain downstream of the Kostanjevica na Krki), and some other necessary infrastructure measures. But, no matter how we tried, we could not assure the desired results in flood risk reduction only or mostly with the additional activation of the floodplains.

Namely, the floodplains along the Krka river and in the Krakovski forest are already rather active at lower return periods. According to simulations, additional activation does not yield any significant improvements in flood risk. River bed deepening of the northern stream of the Krka river has no perceivable effect on floodwater depth decrease. The Scenario 3, which activates the floodplains to their maximum possible extend, does yield significant improvements in flood hazard in Kostanjevica, but the estimated costs are prohibitively expensive, and we believe the scenario is not feasible.

In the future, we intend to explore some more options for the purpose of flood risk reduction in the pilot area (such is the construction of temporary precast walls installed only when a flood is expected).

Nevertheless, the results and the experiences gained from the project Danube Floodplain so far will significantly help us in preparation of the Floodplain management Manual, the Catalogue with win-win restoration and preservation measures, and DRB Sustainable Floodplain Management Strategic guidance. Such a framework will provide a solid foundation to stakeholders in flood risk management planning, considering floodplains as an important factor for flood risk reduction with the emphasis on water protection and nature conservation.