**5. Conclusions**

A study has been conducted examining inter- to intra-annual nearshore bar dynamics on the open-coast of Kamchia-Shkorpilovtsi sandy beach at the Bulgarian Black Sea as influenced by regional wave climate, making use of field measurements of seabed morphology, numerically modeled wave data at different time scales and examination of the influence of different telecommunication patterns.

It has been shown that in 2009–2010 on an intra-annual time scale the cross-shore bar (crest) migration followed a certain repetitive seasonal pattern, mainly determined by nonlinear transformation of waves in the coastal zone. During summers, the bar retained its stability farthermost off the shore due to weakly non-linear and low-energy wave regimes. At the same time, the most active in the view of crest displacements are autumn-winter and winter-spring periods in both years, as closest to the shore the outer bar was in winter with minor seaward and shoreward shifts near its reference location. It has been revealed that highly non-linear wave regimes and scenarios of waves transformation are responsible for cross-shore bar migration having wave steepness >0.03, significant height over 1 m and peak period more than 6 s. Even though these threshold values were determined based on hindcast monthly average data their validity has been supported by recent scientific studies at the site, as drawing of more precise thresholds could be secured by regular wave and beach profile measurements and analysis. Furthermore, the results on the influence of storms on the bar migration revealed that direction of crest displacement primarily depends on the wave period, the duration of wave conditions with Hs/Lp > 0.04, angle of wave incidence and total duration of storms. Thus, among the studied storms having rather similar average significant heights, those moving the outer bar seaward had longer periods (7.2 s), twice as long duration of retained over 0.04 steepness (121 h), lasted by ≈20% longer and were predominantly approaching from E-ENE, as opposed to storms

with more oblique angle of incidence NE-ENE displacing the bar shoreward. On annual basis the bar evolution was found the be mainly governed by wave height and storms' parameters as angle of approach and duration, since the predominance of oblique wave incidence and longer storm duration in 2009 could be responsible for shoreward shift of bar evolution pattern and increase of depth above its crest. It is appropriate to comment that according to [74] seasonal fluctuations of individual profiles could be as pronounced as alongshore variations of a rhythmic seabed topography, which recently has been confirmed in [15] based on field observations and numerical modeling.

Results concerning the possible connection between the temporal periodicity of Q99Hs and variability of the climatic indices showed that for all time spans, the regional wave climate would be most influenced by the EA and the EA/WR indices. Thus, it is expected that mean inter-annual outer bar location may vary depending on the periods of maximum annual wave height fluctuations, which in turn predominantly depend on the climate indices the EA (4–5, 10–11, 20–30 years) and the EA/WR (2–4, 9–13 years), but also may be affected by the AMO (3, 13 years), the AO (3, 15 years) and the SCAND (2, 20–30 years). The presented results for the first time demonstrate a connection between the climatic indices and the nearshore bar position for the Bulgarian Black Sea coast.

**Author Contributions:** Writing of the paper, data processing and analysis, visualization of results, N.A.; Article main idea, analysis of climate change and teleconnection patterns, visualization of results, preparation and writing of one section of the paper, Y.S.; SWAN modelling, hindcast data processing and analysis, N.V.; XBeach modelling, experimental data processing and analysis, visualization of results, P.E.; Analysis of climate change and teleconnection patterns, S.K. All authors contributed to interpretation of results, provided critical feedback and helped shape the research. All authors participated in field experiments on the study site. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was partly funded by RFBR, grant number 20-55-46005.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** This research was supported by 'National Geo-information Center for monitoring, evaluation and forecasting of natural and anthropogenic risks and disasters' within the Program 'National Roadmap for Scientific Infrastructure (2017–2023)' of Republic of Bulgaria, Contract № ДO1-282/17.12.2019; The research was also performed in the framework of Russian Federation state assignment theme № 0128-2021-0004.

**Conflicts of Interest:** The authors declare no conflict of interest.
