## 3 Methodology and Database
### Database Acquisition  
The model proposed and implemented in this study is based on two essential databases in terms of the assessment of erosion and territorial development of ravines, as follows: the digital elevation model (DEM) that highlights the shape and morphometric characteristics of the ravine, and the simulated hydrograph drainage that has the peak equal to the maximum flow that contributes to the erosion, namely the flow to full banks [42]. The importance of a high-precision and accurate morphometric representation is essential in spatial analysis GIS models for identifying critical areas and issuing technical solutions to recover them. In this presented model, it was decided to obtain the DEM as the main spatial database input within the complex model using the UAV technique [43]. This technique for obtaining spatial databases was chosen because it fits perfectly in terms of costs and time allocated to this stage, in order to reduce the time used and maintain the relatively low costs. Another important reason for the implementing of the UAV technique is that torrential area in the form of ravines has a relatively small spatial extent both in terms of longitudinal development and in terms of the total area developed. Thereby, with the help of drones, which have an average flight range, photos can be purchased at a high resolution so that the obtained output will consist of an accurate digital elevation model. Figure 2: Methodological flowchart. The equipment used for the acquisition of the spatial database representing the topography of the analysed ravine is the DJI Phantom 4 Pro UAV system (DJI, Nanshan, Shenzhen, China) equipped with a battery that ensures a flight autonomy of approximately 25 min and a camera that allows the acquisition of photos with a resolution of 20 megapixels as well as the GNSS system Geomax Zenith 35 (GeoMax, Widnau, Switzerland). The correct acquisition of the databases taken with the help of UAV technology firstly requires a very good analysis of the targeted area for making decisions regarding the realization of the flight plan of the drone, the choice of the overlap coefficient of consecutive and adjacent images, the territorial placement of ground control points (GCP) used in the georeferencing process and the placement of control points used in the process of calculating the errors. Regarding the flight mission, a double flight plan oriented in the direction of NNV-SSE and NNE-SSV was opted for, with a camera orientation angle of 45 degrees, which helps to capture all the details of the analysed ravine, including the general configuration in terms of its longitudinal spatial extension, as well as the banks slope, with a flight height of 50 m (Figure 3A). To increase the accuracy of the digital elevation model, a number of nine GCPs and three control points were placed and chosen to identify georeferencing errors, points measured in RTK mode (in the metric coordinate system Stereographic 1970; Romania national projection system) with real-time corrections receiving from the fixed station Cluj-Napoca. The GNSS system used was the GeoMax Zenith35 Pro (GeoMax, Widnau, Switzerland), and the targets were marked on the ground with green fluorescent spray in order to be more easily identified in the processing/reference stage (Figure 3B). In recent decades, GNSS systems became the perfect choice for topographical surveys and precise measurements of points on the surface of the earth used to geo-reference. GNSS systems are conditioned to optimal field conditions such as sufficient satellite availability, network RTK services and open field [43]. The high precision of the required representation is obtained as a result of georeferencing the obtained images after performing the flights based on GCP. Therefore, we measured the following points in the field: 100, 101, 102, 103, 105, 106, 107, 108 and 110. The choice of ground control points in the territory was made in such a manner as to be evenly distributed in the territory and to cover the entire analysed area (Figure 4).