## 4 Discussion
### UAV Surveys as a Part of Multi-Platform Environmental Monitoring of the Lake Sevan Coastal Zone
Best practices for such monitoring in many coastal environments are based on the use of hierarchic multi-scale and multi-platform approaches, integrating data with differing spatial resolutions and spectral ranges, obtained from various sources with different periodicity [2; 6; 27; 53]. Taking into consideration specific features of the study site and the totality of local environmental problems, the proposed monitoring system could adopt the structure presented in Table 3 with respect to the capabilities of acquiring and processing satellite and UAV data. It should be emphasized that the proposed system relies mainly on open satellite imagery or data, freely accessible through research and educational licenses. Highly detailed optical surveys, which can be performed rapidly by means of compact, low-budget UAVs, play a prominent role in the proposed system. Such surveys can be carried out by personnel of environmental institutions or volunteers without special pilotage skills, making it possible to obtain ultra-high resolution data for various territories at very frequent intervals. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Thematic Task** & \begin{tabular}{c} **Spatial Scope** \\ **(Spatial Resolution)** \\ \end{tabular}  & **Periodicity** & **Platforms** \\ \hline \multirow{6}{*}{Monitoring land use} & \begin{tabular}{c} Drainage basin \\ 10–30 m \\ \end{tabular}  & Annually & \begin{tabular}{c} Multi-spectral \\ multi-seasonal satellite \\ data (Landsat 8 OLI, \\ Sentinel-2 MSI) \\ \end{tabular}  \\ \cline{2-4}  & \begin{tabular}{c} Coastal zone \\ 1–3 m \\ \end{tabular}  & Annually & \begin{tabular}{c} Annual mosaics of highly \\ detailed satellite imagery \\ \end{tabular}  \\ \hline \begin{tabular}{c} Monitoring pollution \\ point-sources in the \\ coastal zone and \\ their state \\ \end{tabular}  & Coastal zone (1–3 m, first cm) & Annually and on request & \ \begin{tabular}{c} Annual mosaics of \\ highly detailed satellite \\ imagery and on-demand \\ UAV-derived imagery \\ \end{tabular}  \\ \hline \multirow{6}{*}{Monitoring spontaneous littering} & Coastal zone outside of \\ developed recreation \\ facilities & Weekly and on request \\ (better than 0.1 m) & \\ \hline \multirow{6}{*}{Monitoring of shore erosion} & Infrastructure and \\ communication facilities & Daily and on request \\ in the coastal zone and \\ adjacent areas & (better than 0.1 m) & \\ \cline{1-1} \cline{2-4}  & Waterlogged or \\ submerged and flooded & submerged coastal \\ shores & habitats \\ (better than 0.1 m) & \\ \hline \multirow{6}{*}{Monitoring the \begin{tabular}{c} submerged and flooded \\ shores \\ \end{tabular}  } & Water body of Lake \\ \cline{1-1}  & Sevan, \\ \cline{1-1}  & 250–300 m & \\ \cline{1-1}  &  
Applications of UAV-Derived Highly Detailed Optical and Thermal Data for Monitoring Coastal Processes  
The key findings of conducted UAV-derived multi-temporal data analysis have demonstrated that the currently changing water level of Lake Sevan leads to a rather uneven distribution and intensity of coastal processes along the shoreline. First, the rise in water level entailed activation of destructive shoreline processes, resulting in broader development of erosional coasts. Our calculation of short-term (one to two years) parameters of shoreline at key sites revealed that destruction of shores classified as present-day erosional is highly intensive. The rate of shore erosion exceeds 3.5 m/year in some places such as forested cliffs of Cape Tsovinar along the Major Sevan coast. The prevailing contemporary coasts along Lake Sevan are accumulative coasts (Table 2). They are mainly submerged due to the present water level rise but show rates of shoreline destruction significantly lower than those of erosional coasts. Some coastal sites display current activity of shore accretion, compensating the water level rise and inducing the broadening coastal areas. In the formation of present-day coasts, a significant role is played by biogenesis factors.