**1. Introduction**

Flood risk managemen<sup>t</sup> and protection infrastructure does not comprise an exclusively technical subject. The implementation of flood risk managemen<sup>t</sup> strategies and their societal integration and acceptance necessitate flood governance. The catchment area of the project, the Strymon River basin in northern Greece, has suffered numerous flood events of varying importance in the past decades with consequences on the natural and socioeconomic sectors. At the European Union (EU) scale, the gradual employment of the Water Framework Directive (WFD) (EC 2000) since the early 2000s and the Directive on the Assessment and Management of Flood Risks (EC 2007), commonly known as the Floods Directive (FD), have provided a critical legislative framework that has led to the development of operational tools, such as the Flood Risk Management Plans (FRMPs) [1].

The FRMPs are the first step in compliance with the European Legislation in the hierarchical pyramid of flood managemen<sup>t</sup> and protection. Their objectives set for flood risk managemen<sup>t</sup> focus on reducing the potentially negative consequences that floods have on human health, the environment, cultural heritage, and economic activity, as well as on initiatives to reduce flood occurrence [2]. Although they offer a fundamental plan, their macroscopic perspective in terms of scale does not always give precise results when dealing with large-scale areas.

In order to assess the necessity of flood protection infrastructure on a local scale, further technical and operational data should be coupled together with those derived by the FD. These data include specific information on infrastructure with the site-specific location,

structural characteristics, the initial cost of construction, performance, the response to flood events, and the cost of maintenance and reconstruction.

In cases in which structural flood protection measures fail to serve flooding inhibition, the results may affect different sectors, depending on the intensity and extent of the flood event [3]. Material damage is the most common consequence of infrastructure failure, and it has a direct economic impact in that it requires financial resources to be repaired or reconstructed in order to continue to provide the required amount of protection in the future.

The aim of the research is to demonstrate the importance of evaluating the operability of existing flood protection structures in future anti-flood planning at regional and local scale. The operability is evaluated as a synthesis of flood occurrences, cost of structures and cost of structures' maintenance.

### **2. Materials and Methods**

The tools for assessing the financial cost of repairing damage or failure of technical/structural works constructed for flood protection are critical assets in flood project managemen<sup>t</sup> by the governmental authorities and public organizations engaged. These tools can provide spatial data linked to construction and repair costs for identifying problematic spots and areas that repeatedly show a structural inability to prevent flooding. Particularly, the identification of linkages among spatial data, costs of flood protection works and flood event occurrences could highlight the regions or locations that the current flood protection infrastructures are not effective since flood events continue to occur The outcome of such a process may lead to a flood risk assessment tool that can record information that supports decision-making procedures in order to formulate action and managemen<sup>t</sup> plans related to flood planning [4].

This study was part of the project "Evaluation of the performance and interoperability of flood protection intervention measures in the area of the Strymon river basin", which was implemented under the INTERREG V-A European Territorial Cooperation Program "Greece-Bulgaria 2014–2020 "Flood Protection—Cross Border Planning and Infrastructure Measures for Flood Protection"; this program aimed to combine the FRMPs with a thorough and detailed record and evaluation of the existing situation in terms of flood protection infrastructure to assess the majority of civil works and previously applied measures in order to evince the areas prone to flooding and provide an Action Plan, in which specific located measures were proposed according to a hierarchical evaluation.

### *2.1. Study Area*

The study was implemented in the catchment area of the Strymon river, with an emphasis on places that show higher flood risk. Strymon is a river of the Balkan Peninsula with a length of 360 km, of which 242 km are in Bulgarian and 118 km are in Greek territory. The total hydrological basin has an area of 16,550 km2, with only 6344 km<sup>2</sup> located in Greece [5].

The area has suffered numerous flood events, with an increasing intensity of occurrence in the last decade. A results-based approach offers a tool for priority-based planning in which the initial cost of investment in the construction of flood protection work is related to the potential economic failure consequences and the repeated costs of maintenance. Numerous flood events, with an increasing tense of occurrence in the last decade [6] is presented in the case study area, with Figure 1 presenting all the flood events during the period 2012–2018 where official data are available [7].

**Figure 1.** Study area and flood events during 2012–2018.
