SPATIAL AND MULTIANNUAL ALTERATION OF WAVE EXPOSURE ALONG THE BULGARIAN COAST AS INFERRED BY NUMERICAL MODELLING OF WAVE ENERGY TRANSPORT

Abstract

Knowledge of the coastal hydrodynamics, in particular the storm induced waves, is essential for management of the extremely vulnerable coastal environment. There, wave processes dominate surge, coastal currents, sediment transport and species distribution. Therefore, it is important to have a detailed insight into the exposure of different coastal areas to wave action. The study proposes a wave exposure classification of the Bulgarian Black Sea coast according to wave climate conditions as required by the Water Framework Directive (WFD), which focuses on ensuring good qualitative and quantitative state of water resources and ecosystems. To this end, the coast was divided into twenty-five coastal units while the applied methodology is based on numerical modelling of wave processes employing the third-generation SWAN wave model forced by wind fields spanning the period 2007-2018. The energy transport (power) of waves entering the coastal environment was estimated, which is considered an indicator for wave exposure. Furthermore, the study period is divided into two 6-year cycles, which allowed for capturing of the climatic wave fields alteration thus enabling to detect possible climate change effects. Spatial alteration of the energy transport maxima and, accordingly, wave exposure is reviewed. Results show that the northern most, middle and southern parts of the coast are the most exposed to wave action. The coastal orography, shore geographical orientation and beach slope depth have a foremost importance for the exposure type. When using the numerical modelling tools these factors are accounted for with the required level of accuracy.