The key study or the basis for taking decisions on the continuation of flood protection actions at the level of entire cross-border river basins is the so-called comprehensive flood study. The main objectives of the study are an integrated assessment and determination of optimal variants of long-term flood protection measures for flood risk management. In this regard, hydrological, hydraulic, environmental and technical-economic verification of the costs and benefits of structural and non-structural flood protection measures at the level of the entire river basin must be considered. Of special importance is the fact that all six cases of river basins are so-called cross-border river basins, whereby the whole river basin is not in only one country, but in both Slovenia and Croatia (and also in other countries as in the case of the Mura and Drava); therefore, such decisions can be taken only within the framework of jointly prepared, conducted and completed comprehensive studies.

The study includes an analysis of the existing situation, an analysis of the objectives of the flood risk management, analysis, assessment and comparison of alternative options, and a determination of an optimal combination of flood protection measures for long-term risk management in the river basins concerned. The study also identifies the main areas for natural retention or spilling of high waters and the analysis of potential, economically viable and in other aspects feasible, measures of green infrastructure.

When deciding on the implementation of structural flood protection measures, the natural hydromorphological characteristics of watercourses are preserved to the maximum possible extent. In addition to the investment costs, the estimated cost of flood protection measures includes running costs (e.g. operating, management and maintenance costs of the water infrastructure or operating, management and maintenance costs of the hydrological forecast system), the environmental costs of an individual flood protection measure and the cost of water as a natural resource.

Commonly and in a coordinated way, prepared comprehensive flood protection studies for the cross-border river basins of Dragonja, Kolpa, Bregana, Sotla, Drava and Mura will present long-term guidelines agreed by two countries for flood protection activities in these river basins in the future.