*2.2. Methodology*

The methodological approach constituted of the elaboration of the following actions and activities:


All data were introduced into a web GIS (Geographic Information System) for visualization and analysis.

### **3. Results and Discussion**

In cases in which past construction data are needed, the main obstacle is the scattered records among the responsible public authorities and the lack of service files. Despite the difficulty of the venture, 652 structural flood protection measures and civil works were recorded in total through field surveys and file searches, constituting the first effort of such a scale in the Greek territory.

These structures were further divided into 21 subcategories according to the type of structure and the frequency at which they occur in the river basin. The occurrence frequency is indicative of the structural type preferred and most constructed in the area. Figure 2 illustrates all categories of structural measures as well as their types and occurrence frequencies in the study area.

**Figure 2.** Protection infrastructure according to structure type and occurrence frequency.

All aforementioned data were mapped in QGIS while the geodatabase was populated with information relative to each structure, such as the construction date, cost, maintenance frequency, failure, damage, repair cost, and interoperability with other structures. Figure 3a–c show the mapping outcome of the structure data and their reclassification into six main categories—(i) restoration work, (ii) urgen<sup>t</sup> projects, (iii) dredging work, (iv) cleaning work and work on technical islets (in rivers), and (v) alluvial removal work— according to the type of maintenance necessary over a period of 5 years. Maintenance work included any kind of intervention needed once, while the repeatability of maintenance in a specific structure/location was also recorded, thus providing an index of vulnerability and poor resilience of each structure to flooding events (Table 1).

**Figure 3.** Infrastructure mapping (**a**) and maintenance (green mark) /intervention (red mark) repeatability (**b**) in the Strymon river basin.

In total, all 652 recorded flood protection structures showed a repetitive need for intervention actions to be taken due to possible failure or unsuccessful operation at an approximate rate of 1:3, while in most cases, maintenance work needed to be repeated with the reverse rate of 3:1. Two categories proved to show more vulnerability and less of an ability to perform well in potential flooding: (a) restoration work in critical flood protection infrastructure and (b) bridges and stream crossings.


**Table 1.** Flood protection infrastructure and maintenance interventions.

The above were introduced into the GIS model in order to determine the spatial distribution of the data and have a visual outcome that yielded critical locations subject to further study; these locations showed an increased vulnerability to flooding events, as demonstrated by the data.

Figure 3 presents the mapping outcome of infrastructure data visualization (a) and reclassification, with the repeatability of maintenance marked for each structural work (b) related to the number of interventions.

In addition, important information on the initial cost of infrastructure and the maintenance cost was collected. While the initial cost was not always available due to the construction in past years, the maintenance costs for the past decade were easier to obtain. The analysis of the outputs is depicted in Figure 4.

**Figure 4.** Task repeatability ranking by approximate labor cost (EUR).

The first time a flood protection task is implemented, the restoration work showed a significantly higher cost of EUR 431,000.00, while the repetition of the work/intervention measures placed the interventions in bridges and culvers in the first place with a significant difference. The work on islets showed the lowest cost, implying that it has not ye<sup>t</sup> been necessary to modify them (based on repeatability). The total approximate cost for the maintenance of flood work only rose to EUR 42,711,000 in a 5-year period.

The significance of the structural work and the prioritization of needs in new flood protection infrastructure was also correlated with the FRMPs; all data were overlayed with the food risk zones to spatially determine the most vulnerable infrastructure [9] so as to hierarchize potential interventions.
