## 3 Results
### The 1% Floodplain and Hazard Mapping  
The 1% floodplain has been defined dimensionally and spatially by performing hydraulic calculations based on the flow corresponding to the 1% exceedance probability (Q1% = 230 m\({}^{3}\)/s, recorded at Tohanu Nou SH), with a statistical return period of 100 years. The topographic data used to build the HEC-RAS one-dimensional model were materialized by a set of 139 cross-sectional profiles, of which 126 were drawn on the Turcu River, over a length of 20,401 m (Figure 3). The average distance between cross-sections on the Turcu River was 161.91 m. The distances between profiles depend on the sinuosity of the river. The method of drawing cross-sections requires that where the river is straighter, the distance between two consecutive cross-sections can be increased. In order to describe more precisely the geometry of the main river channel, additional cross-sections were required on the meandering sections of the river. These sections cover at least the width of the river but also the possible flooding area. Field observations have allowed, within the major bed along the profile drawn at Tohanu Nou HS, the identification of relatively thick sapling thickets with rare and young trees (Figure 4). Thus, the values of the Manning roughness coefficient (n), used for the calculations, were taken from the range 0.040-0.080, according to the classification proposed by [PERSON] in 1959 [53; 63]. For the flow value of 230 m\({}^{3}\)/s and \"n\" (Manning's roughness coefficient) = 0.060, the corresponding water level (h1%) in the design profile was 690.19 m absolute elevation, 2.295 m above the level of the talveg point within the section (Figure 5). The computed elevation values for the plotted cross-sectional profiles refer to the DEM elevation, which shows a tolerable error of about +1 m compared to the GPS measured elevations in the talveg at the Tohanu Nou SH hydrometric sight (687.895 m on the DEM--686.889 m above the Black Sea 1975 Constanta Height Datum, measured with GPS = +1.006 m). Figure 3: Geometric model of the river section studied, obtained using the extension HEC-GeoRAS, for Esri Arc GIS/ArcMap software. The bed roughness coefficient values are some of the more important aspects of any hydraulic model. They help to correctly define the extent of the floodplain and the velocity of flow in the main river channel. It is almost impossible to determine the roughness by in situ measurements; thus, values of this coefficient are usually estimated from alternative sources such as geological maps, pedagogical maps, orthophotos or satellite images [64,65]. Based on the geomorphological characteristics of the riverbed, the rock types [66] in which  
Figure 4: Minor bed morphology and vegetation characteristics from Tohanu Nou hydrometric station. Figure 5: Highlighted water level (h1% = WS PF1 = 690.19 m) for Q1% (Total Q = 230 m\({}^{3}\)/s) in the calculation profile of Tohanu Nou SH. the minor riverbed is deepened and the land cover/use of the major riverbed, as well as roughness coefficient values, were used according to the classification proposed by [PERSON] (Table 1). Satellite images used for the land classification and roughness coefficient assignment were viewed using Google Earth Pro. The images, dated 16 September 2019, 27 August 2020 and 21 September 2020, covered the entire study area. The use of specialized software allowed for the realization of the defining elements of the bed geometry, the calculation of the water level in the transverse potholes, as well as the visualization of the results of the one-dimensional hydraulic model, resulting in the vector and raster database corresponding to the 1% floodplain. The determination of the hazard magnitude on 3 water depth intervals within the 1% floodplain was suggested by the methodology implemented at a national level. By superimposing the thematic layers related to intra-village areas and roads, the flood hazard map for the Turcu River was obtained (Figures 6-8).