## 3 Results
### Coastal Types and Processes  
Monitoring of shoreline and beach processes as well as comprehensive environmental monitoring of the coastal zone is often associated with the use of various remote sensing (RS) platforms [27; 53]. Some problems emerge in the course of monitoring rapid coastal processes when situations change quickly due to hydrometeorological conditions, dynamic properties of objects, and phenomena themselves. In those cases, there is an issue to acquire simultaneous or repeated RS data with high spatial resolution from existing satellite platforms. In the course of our UAV surveys, the shoreline position was primarily detected (at 84.4 km along the entire Lake Sevan coasts) because the slightest changes can trigger a chain of negative processes influencing the state of lacustrine environments. Changing the water level in Lake Sevan continues to entail significant transformations of immunological and hydro-ecological parameters, especially trophic status, the structures of coastal wetland, and aquatic ecosystems [37; 38; 39]. Changes in rate and type of coastal processes (erosion, waterlogging, and flooding) lead to the rapid degradation of coastal habitats and formation of dead biomass, thus, creating favorable conditions for phytoplankton development [39]. Based on collected field data in 2018-2019 (UAV-derived aerial imagery, terrestrial photography of reference points and field observations sites), combined with GeoEye-1 image (2017), present-day coastal types were identified and mapped at a large scale. Coastal types were determined in accordance with two classification schemes developed by Russian geomorphologists [54; 55]. Classification based on shore genesis [54] allows specifying the presumed genesis of shores in their initial state. The shores developed under wave effects can be divided in three coastal types by currently dominating shore processes [55]. Present-day coastal types of the Lake Sevan and their relative distribution are presented in Figure 6 and Table 2.  
Erosional coasts of the Norashen and Isovinar peninsulas, which are under the effect of active transformation, as well as the shores developed under the effect of permanent stream accumulation of the Masrik River, were surveyed repeatedly in 2018-2019 every six months to more accurately determine the dominant coastal processes by comparison of shoreline positions. Our modified Hausdorff distance calculations for the key coastal sites show that the net changes in the shoreline position for erosional cliffs of the Isovinar between September 2018 and July 2019 were \(-2.91\) m on average, giving the annual rate of shore retreat as 3.65 m with a standard error of 0.87 m.  
We also modeled the shoreline position and assessed the rate of coastal processes: under the scenario of increasing the lake level to 1903.5 m as a result of full implementation of the relevant law [34]. The resulting flooding would threaten three hotels, five industrial facilities, and 171 single buildings in the coastal zone (Figures 7 and 8). There are approximately 70 km of hard-surfaced roads situated along coasts intensively affected by abrasion. Coastal forests totaling 13.87 km\({}^{2}\) are at risk of degradation due to active shore erosion. \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{2}{c}{**Coastal Types by Genesis and Dominating Processes**} & \multicolumn{2}{c}{**Length of the Total Coastline, \%**} \\ \hline \multirow{3}{*}{developed under wave effect} & accumulative coasts & 38.6 \\ \cline{2-3}  & erosional coasts & 28.1 \\ \cline{2-3}  & coasts with active shore erosion & 17.8 \\ \cline{2-3}  & and accumulation & \\ \hline developed under the effect of & marsh coasts & 10.1 \\ \hline developed under the effect of & & \\ permanent stream accumulation & fluvial coasts & 5.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Present-day coastal types and their distribution by length along the Lake Sevan shoreline.