## 3 Methodology and Database
### Database Acquisition
The control points 104, 109, 111 are necessary for the evaluation of the degree of accuracy and were chosen randomly both inside and outside the ravine to correctly highlight both planimetric X and Y errors, as well as altim  
Figure 3: (**A**) Fly plan; (**B**) GCP and CP marks. Following the processing of pre-calibrated images [13] obtained as a result of performing the flight, based on AGISoft software v.1.7.0, and using GCPs as georeferencing points, the main input database within the digital model of spatial analysis and elevation was obtained, represented by a raster grid with a resolution of 3.86 cm, which has very few positioning errors (0.065 m/X axis, 0.053 m/Y axis and 0.075 m/altitude). The digital elevation model obtained at such a precision and with a very high resolution denotes high quality in terms of spatial-territorial location and high fidelity of the 3D representation, reflected in the high accuracy of the result. The recommended database is used in studies conducted on a large topographic scale and in hydro-ameliorative projects. Another particularly important database in terms of assessing the current stage of erosion and modelling by simulation of the main hydro-amelioration interventions to reduce the negative effects is represented by the maximum flow through the respective ravine. This debit generates the maximum flow rate and the maximum erosion power. The maximum erosion power generated by the drainage flow has a direct influence on the depth erosion of the ravine banks, and the flow rate has an influence on the mode of transport and deposit of eroded material. In order to establish the GIS model of spatial analysis in the present study, as well as in most spatially identified ravines with direct impact on the adjacent lands, there are no maximum precipitation intensity data available in order to calculate the maximum probable flow. Since the analysed ravine is not controlled from a hydrometric point of view, it was decided to introduce the maximum simulated flow in the section that is most vulnerable and exposed to erosion in the spatial analysis process. In order to identify the  
Figure 4: GCP and CP location inside the study area; obtained errors. maximum simulated flow that would have erosive effects to the upper part of the banks (bankfull discharge), the calculation was based on [PERSON]'s formula:  
\[\mathrm{Q}=\frac{\mathrm{A}}{\mathrm{n}}*\mathrm{R}^{\frac{2}{3}}*\mathrm{S}^{ \frac{1}{2}} \tag{1}\]  
where  
Q--discharge [m\({}^{3}\)/s],  
A--active channel cross-section area,  
R--hydraulic radius,  
S--slope (1/m),  
n--roughness coefficient. Thus, in the section chosen as the most vulnerable, the transversal profile was drawn based on the digital elevation model obtained with UAV techniques, extracting all the necessary parameters for the implementation of the formula and then obtaining the maximum flow in that calculation section (Figure 5). Based on the informational resources obtained after marking the transversal profile on the digital elevation model, as well as a result of the direct field measurements, the following parameters were obtained for calculating the maximum flow: bottom flow 1.5 m, right side slope 0.448, left side slope 0.172, flow depth 1.26 m, channel slope 0.001, channel rugosity (Manning's roughness coefficient) 0.045. The integration of the parameters in the formula for calculating the maximum flow based on the Manning equation allowed the calculation of the maximum simulated flow with the value of 1.55 m\({}^{3}\)/s. This simulated flow will be used for the calculation and spatialization of the analysed parameters within the initial evaluation process of the ravine as well as within the three simulations performed in order to identify the best hydrotechnical works for arranging the analysed ravine. The presented data were used to calculate the flow in the cross section, with the Manning coefficient and the value of the simulated flow further used as input databases in the hydraulic analysis based on HEC-RAS software v.5.0.7 presented in Section 3.3.