Nataliya Andreeva | Institute of Oceanology-BAS (original) (raw)

Papers by Nataliya Andreeva

Research paper thumbnail of D5.1 Report mapping the governance status quo in pilot sites

Coastal regions provide some of the most productive and biodiverse environments with an important... more Coastal regions provide some of the most productive and biodiverse environments with an important and often underappreciated carbon storage potential. At the same time, they are among the areas of highest population density, natural assets and cultural heritage in the world, yet are experiencing significant social, economic and environmental challenges, exacerbated by climate change and human pressures.The REST-COAST project (Large scale RESToration of COASTal ecosystems through rivers to sea connectivity) will demonstrate to what extent upscaled coastal restoration can provide a low-carbon adaptation, reducing risks and providing gains in biodiversity for vulnerable coastal ecosystems, such as wetlands or sea grass beds. By overcoming present technical, economic, governance and social barriers to restoration upscaling, REST-COAST will develop the large scale river-coast connectivity and increase the nearshore accommodation space for the resilient delivery of coastal ecosystem servi...

Research paper thumbnail of D4.1 Scorecard methodology (tool) for coastal system restoration effects on ESS and BDV

Research paper thumbnail of On Sea Waves� Properties Measured in Burgas Bay Transitional Waters, Black Sea

23rd SGEM International Multidisciplinary Scientific GeoConference Proceedings 2023, Water Resources. Forest, Marine and Ocean Ecosystems, Vol 23, Issue 3.1

The study presents results and discuss statistical properties of wind-generated sea waves measure... more The study presents results and discuss statistical properties of wind-generated sea waves measured in transitional waters of the Burgas Bay at the Bulgarian Black Sea. Wave measurements were acquired by Acoustic Doppler Current Profiler at two locations offshore Kraymorie and Chernomorets at water depths of approx. 15 m and 18 m, respectively. At each location, data were recorded for about three and a half months in winter seasons of 2021-2022 in front of Chernomorets and in 2022-2023 offshore Kraymorie, when storm activity intensifies posing higher risk of flooding, erosion and the threat to human activities along the coast. The study examines in statistical terms variability of significant wave height, peak wave period, mean wave direction and their interdependence. It also explores the storm activity during both periods of data collection in terms of wave height, storm duration and direction. Analysis includes clustering wave parameters as joint frequency of occurrence as percent...

Research paper thumbnail of On sea waves' properties measured in the Burgas bay transitional waters, the Black Sea

Proceedings of 23rd International Multidisciplinary Scientific GeoConference SGEM 2023, 2023

The study presents results and discuss statistical properties of wind-generated sea waves measure... more The study presents results and discuss statistical properties of wind-generated sea waves measured in transitional waters of the Burgas Bay at the Bulgarian Black Sea. Wave measurements were acquired by Acoustic Doppler Current Profiler at two locations offshore Kraymorie and Chernomorets at water depths of approx. 15 m and 18 m, respectively. At each location, data were recorded for about three and a half months in winter seasons of 2021-2022 in front of Chernomorets and in 2022-2023 offshore Kraymorie, when storm activity intensifies posing higher risk of flooding, erosion and the threat to human activities along the coast. The study examines in statistical terms variability of significant wave height, peak wave period, mean wave direction and their interdependence. It also explores the storm activity during both periods of data collection in terms of wave height, storm duration and direction. Analysis includes clustering wave parameters as joint frequency of occurrence as percentage across predefined intervals to reveal their distribution in the time-span of measurements.

Research paper thumbnail of Identification of Coastal Flooding Hotspots in a Large Bay Using an Index-Based Risk Assessment Approach

Lecture notes in networks and systems, 2023

The study aims to assess in probabilistic terms the magnitude of storminduced flooding hazard and... more The study aims to assess in probabilistic terms the magnitude of storminduced flooding hazard and vulnerability along Burgas regional coast (Bulgaria, western Black Sea) and to identify susceptible coastal sectors (hotspots). It employs the Coastal Risk Assessment Framework-a screening process that allows estimation of hazar'1d intensities, extents and potential receptors' exposure vulnerability within predefined sectors. Total water level, consisting of maximum wave run-up estimated using empirical models relevant for sandy beaches, artificial or rocky coastal slopes and storm surge level, is considered for calculation AQ1 of coastal flooding hazard. Furthermore, hazard extents (flooded areas) are determined by two approaches to form the hazard indicator, while land use, social vulnerability, transport systems, utilities and business settings are considered as exposure indicators. Finally, the potential risk is assessed by combining the hazard and exposure indicators into a single index, thereby allowing rapid comparison of coastal sectors' vulnerability. The study found that the main concentration of hotspots is in the town of Pomorie and its surroundings, while other candidates are scattered across the innermost Burgas bay.

Research paper thumbnail of Autoregresive (AR) bispectra of wind waves in the coastal zone

Comptes rendus de l’Acad´emie bulgare des Sciences, 2007

The paper examines the second-order non-linearity of the wind waves by bi-spectral analysis based... more The paper examines the second-order non-linearity of the wind waves by bi-spectral analysis based on non-parametric (conventional) and parametric approaches.
The parametric technique is presented by model that is in the class of auto-regressive
(AR) processes. The wave measurements are taken at depth 1.6 m in the coastal
zone of the Bulgarian part of the Black Sea. The bi-spectral estimates are evaluated
by aforementioned approaches and subsequently are compared in order to establish
whether AR modelling is applicable to analysis of the nonlinear wind waves propagating in the coastal zone. The results show good agreement between conventional
and parametric estimates.

Research paper thumbnail of Set-up and validation of a Delft-FEWS based coastal hazard forecasting system

Research paper thumbnail of GIS Hazard Maps - Bulgaria. In: Deliverable 5.1 - GIS-Based Hazard Maps. MICORE WP 5: Early Warning System

This chapter presents the GIS-based hazard maps that are set-up for the project area in Bulgaria.... more This chapter presents the GIS-based hazard maps that are set-up for the project area in Bulgaria. The maps have been compiled by Professor Fridtjof Nansen Institute of Oceanology - Bulgarian Academy of Sciences. The text herein represents an excerpt from Deliverable 5.1 GIS-Based Hazard Maps, WP 5: Early Warning System, project "Morphological Impacts and Coastal Risks Induced by Extreme Storm Events" (Acronym: MICORE), funded under the EU's 7FP, GA No 2002798.

Research paper thumbnail of Influence of Wave Climate on Intra and Inter-Annual Nearshore Bar Dynamics for a Sandy Beach

Geosciences, 2021

The study investigates cross-shore outer sand bar dynamics in an open-coast non-tidal beach at th... more The study investigates cross-shore outer sand bar dynamics in an open-coast non-tidal beach at the Bulgarian Black Sea due to wave climate. On seasonal to short-term (1–2 years) time scale, monthly field measurements of the outer bar profiles were related to respective modeled nearshore wave data. Hereby, seaward-shoreward bar migration was examined depending on the wave forcing, wave non-linearity, wave transformation scenarios, storms and direction of wave incidence. Analysis revealed that intra-annually highly non-linear waves were responsible for outer bar displacement, while the direction of migration depended on wave period, duration of conditions with wave steepness >0.04, angle of approach and total duration of storms. Short-term bar evolution was mainly governed by wave height and storms’ parameters as the angle of approach and duration. The correlation between the outer bar location and wave height annual variations initiated the first for the explored Black Sea region ...

Research paper thumbnail of Cultural Insights into Coastal Risks and Climate Change Resilience of a Society ‘in Transition’

G. Martinez (ed.), Culture and Climate Resilience, Palgrave Studies in Climate Resilient Societies, 2021

The study explores the cultural, socio-ecological, and institutional factors responsible for the ... more The study explores the cultural, socio-ecological, and institutional factors responsible for the present ways of handling natural hazards and coping with climate change challenges in Varna, a coastal city situated on the western Black Sea, Bulgaria. Diving into cultural perceptions of risk, governmental, social, and economic circumstances triggered after the political changes in 1989, and present state of development and implementation of disaster risk reduction, coastal management and climate adaptation legislation framework helped to reveal the main reasons behind the relatively low adaptive capacity and climate resilience of Varna.

Research paper thumbnail of Assessment of Coastal Receptors’ Exposure Vulnerability to Flood Hazard Along Varna Regional Coast

Coastal Engineering Proceedings, 2017

Storms and related disasters are phenomena producing coastal hazards and endangering human life a... more Storms and related disasters are phenomena producing coastal hazards and endangering human life and occupation. The study evaluates coastal receptors’ exposure and their vulnerability to storm-induced flooding hazard along Varna regional coast in Western Black Sea, Bulgaria. The assessment is performed employing the Coastal Risk Assessment Framework (CRAF) developed within EU FP7 RISC-KIT project. It constitutes a screening process that allows determination of susceptible alongshore sectors (hotspots) by assessing relevant hazard intensities, hazard extents and potential receptors’ exposure vulnerability within them by means of coastal indices approach. The ultimate goal is to evaluate potential risk posed by flooding in support to coastal managers, decision and policy makers. Assessment of coastal receptors’ exposure vulnerability is done by exposure indicators approach, using hazard intensities and flooding extents relevant to return period of 100 years. The approach consists of c...

Research paper thumbnail of Prototype of Early Warning System for Coastal Storm Hazard (Bulgarian Black Sea Coast)

Comptes rendus de l'Académie bulgare des sciences: sciences mathématiques et naturelles

Recent natural disasters in coastal areas have highlighted the devastating effects that hazards o... more Recent natural disasters in coastal areas have highlighted the devastating effects that hazards of marine origin can cause. This problem is addressed by set up of an on-line Early Warning System (EWS) for reliable prediction of morphological impacts due to marine storm events in support to civil protection strategies. The system involves a train of hydro- and morphodynamic models, predicting the storm impact on the beach, and a set of indicators, which convert model results in terms of key physical parameters to adequate warnings and series of actions to be undertaken by responsible authorities. The prototype consists of five interconnected key modules and lays the foundation for a greater national scale roll-out by adopting the following principles: using a generic structure adaptable to a range of different coastal environments; using free and open-source software; and tailoring the functionality of the EWS to the needs of end-users.

Research paper thumbnail of A physical model of wind waves in the coastal zone

Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE, 2008

ABSTRACT The variability of the amplitude-frequency structure of wind waves in space and time dur... more ABSTRACT The variability of the amplitude-frequency structure of wind waves in space and time during their transformation in the coastal zone are considered. Wave time series, measured synchronously in 15 points along the wave propagation, obtained at field and laboratory experiments, were used for the analysis. Free surface elevation time series were represented as a sum of first and second harmonics with amplitudes slowly varying in time (or envelopes of the waves of corresponding frequency bands). Relative changes of these amplitudes in space and time were studied also. It was revealed, that at the initial stage of the wave transformation, the changes of amplitudes of the first and the second harmonics are similar and amplitudes of the second harmonics are proportional to the squared amplitudes of the first harmonics. At this stage the variability of parameters of individual irregular waves can be explained by Stokes theory. Nearer to the coast the instantaneous values of the amplitudes of the first and the second harmonics varies in time chaotically and is not possible to construct a simple model of the variability of the parameters of individual irregular waves. The main reason for this effect is the backward energy transfer from the second to the first harmonics of the waves during nearly resonant non-linear triad interactions.

Research paper thumbnail of Spatio-temporal variability of the amplitude-phase structure of storm waves in the coastal zone of the sea

Oceanology, 2009

ABSTRACT The spatio-temporal variability of individual storm waves in the coastal zone is studied... more ABSTRACT The spatio-temporal variability of individual storm waves in the coastal zone is studied. Wave chronograms were presented as sums of the first and second harmonics with amplitudes slowly varying in time, which are envelopes for the waves of the corresponding frequency bands. The amplitude-frequency structure of individual waves was estimated from the variations in the amplitude of the envelopes. Bi-spectral analysis was applied to estimate the phase composition of the waves. It is shown that, in the initial stage of transformation, the fluctuations of the waves of the first and second harmonics are synchronous. The amplitudes of the second harmonics are proportional to the squared amplitudes of the first harmonics. Thus, a simple model is possible for the description of individual waves based, for example, on the generalization of the Stokes theory. As the waves approach the coast, the ratio of the amplitudes of the first and second harmonics in individual waves varies in time chaotically, thus it is not possible to describe individual waves on the basis of a simple model. The main cause of the chaotic variation of the amplitudes is the backward transfer of energy from the highest harmonics to the first harmonics due to the sub-near resonant triad interaction close to the resonance. The phase composition of individual waves depends on the distance propagated by the waves and on the stage (main or backward) of the energy exchange between the nonlinear harmonics.

Research paper thumbnail of Scenarios of nonlinear wave transformation in the coastal zone

Oceanology, 2013

ABSTRACT On the basis of field experiments and numerical modeling, we show that coastal zones are... more ABSTRACT On the basis of field experiments and numerical modeling, we show that coastal zones are classifiable according to manifestations of wind wave nonlinearity, which herein is recognized as periodic energy exchange between the first and second nonlinear wave harmonics depending on the average bottom slope and the Iribarren and Ursell numbers. The results offer a basis for developing vulnerability criteria for the coastal zone taking into account its nonlinear dynamics.

Research paper thumbnail of Past and recent trends in the western Black Sea storminess

Natural Hazards and Earth System Science, 2012

Research paper thumbnail of Critical storm thresholds for morphological changes in the western Black Sea coastal zone

Research paper thumbnail of Measurements and Analysis of Storm Induced Short-Term Morphological Changes in the Western Black Sea

The coastal morphology is highly sensitive to storm-induced impacts. All components of the coasta... more The coastal morphology is highly sensitive to storm-induced impacts. All components of the coastal system-aerial beach and dunes, submerged beach, nearshore bars–undergo changes during an extreme storm event (Sallenger et al., 1985; Morton and Sallenger, ...

Research paper thumbnail of Validation of the WAMC4 wave model for the Black Sea

Coastal Engineering, 2008

Research paper thumbnail of Probability distributions of peaks, troughs and heights of wind waves measured in the black sea coastal zone

Coastal Engineering, 2005

The present paper examines the adequacy of different probability density functions to describe th... more The present paper examines the adequacy of different probability density functions to describe the peaks, troughs and peak-to-trough excursions of wind waves measured in the coastal zone of the Bulgarian part of the Black sea. For that purpose various theories for non-Gaussian random process are applied. Some theories depend on the mean, variance and coefficient of skewness γ3 of the process. Others also take the coefficient of kurtosis γ4 into consideration. The analyzed field data are gathered in the coastal zone of the Bulgarian part of the Black sea with depth decreasing from 18 to 1.3 m. The measurements are carried out simultaneously for 11 points with time series of 20 min duration. The coefficients of skewness and kurtosis in those time series are expressed as functions of depth and spectral peak frequency. Analogous dependencies on depth of other parameters are also found. As a result of the investigation it is concluded that the probabilities of occurrence of large wave crests and heights are underpredicted by all of the theories considered.

Research paper thumbnail of D5.1 Report mapping the governance status quo in pilot sites

Coastal regions provide some of the most productive and biodiverse environments with an important... more Coastal regions provide some of the most productive and biodiverse environments with an important and often underappreciated carbon storage potential. At the same time, they are among the areas of highest population density, natural assets and cultural heritage in the world, yet are experiencing significant social, economic and environmental challenges, exacerbated by climate change and human pressures.The REST-COAST project (Large scale RESToration of COASTal ecosystems through rivers to sea connectivity) will demonstrate to what extent upscaled coastal restoration can provide a low-carbon adaptation, reducing risks and providing gains in biodiversity for vulnerable coastal ecosystems, such as wetlands or sea grass beds. By overcoming present technical, economic, governance and social barriers to restoration upscaling, REST-COAST will develop the large scale river-coast connectivity and increase the nearshore accommodation space for the resilient delivery of coastal ecosystem servi...

Research paper thumbnail of D4.1 Scorecard methodology (tool) for coastal system restoration effects on ESS and BDV

Research paper thumbnail of On Sea Waves� Properties Measured in Burgas Bay Transitional Waters, Black Sea

23rd SGEM International Multidisciplinary Scientific GeoConference Proceedings 2023, Water Resources. Forest, Marine and Ocean Ecosystems, Vol 23, Issue 3.1

The study presents results and discuss statistical properties of wind-generated sea waves measure... more The study presents results and discuss statistical properties of wind-generated sea waves measured in transitional waters of the Burgas Bay at the Bulgarian Black Sea. Wave measurements were acquired by Acoustic Doppler Current Profiler at two locations offshore Kraymorie and Chernomorets at water depths of approx. 15 m and 18 m, respectively. At each location, data were recorded for about three and a half months in winter seasons of 2021-2022 in front of Chernomorets and in 2022-2023 offshore Kraymorie, when storm activity intensifies posing higher risk of flooding, erosion and the threat to human activities along the coast. The study examines in statistical terms variability of significant wave height, peak wave period, mean wave direction and their interdependence. It also explores the storm activity during both periods of data collection in terms of wave height, storm duration and direction. Analysis includes clustering wave parameters as joint frequency of occurrence as percent...

Research paper thumbnail of On sea waves' properties measured in the Burgas bay transitional waters, the Black Sea

Proceedings of 23rd International Multidisciplinary Scientific GeoConference SGEM 2023, 2023

The study presents results and discuss statistical properties of wind-generated sea waves measure... more The study presents results and discuss statistical properties of wind-generated sea waves measured in transitional waters of the Burgas Bay at the Bulgarian Black Sea. Wave measurements were acquired by Acoustic Doppler Current Profiler at two locations offshore Kraymorie and Chernomorets at water depths of approx. 15 m and 18 m, respectively. At each location, data were recorded for about three and a half months in winter seasons of 2021-2022 in front of Chernomorets and in 2022-2023 offshore Kraymorie, when storm activity intensifies posing higher risk of flooding, erosion and the threat to human activities along the coast. The study examines in statistical terms variability of significant wave height, peak wave period, mean wave direction and their interdependence. It also explores the storm activity during both periods of data collection in terms of wave height, storm duration and direction. Analysis includes clustering wave parameters as joint frequency of occurrence as percentage across predefined intervals to reveal their distribution in the time-span of measurements.

Research paper thumbnail of Identification of Coastal Flooding Hotspots in a Large Bay Using an Index-Based Risk Assessment Approach

Lecture notes in networks and systems, 2023

The study aims to assess in probabilistic terms the magnitude of storminduced flooding hazard and... more The study aims to assess in probabilistic terms the magnitude of storminduced flooding hazard and vulnerability along Burgas regional coast (Bulgaria, western Black Sea) and to identify susceptible coastal sectors (hotspots). It employs the Coastal Risk Assessment Framework-a screening process that allows estimation of hazar'1d intensities, extents and potential receptors' exposure vulnerability within predefined sectors. Total water level, consisting of maximum wave run-up estimated using empirical models relevant for sandy beaches, artificial or rocky coastal slopes and storm surge level, is considered for calculation AQ1 of coastal flooding hazard. Furthermore, hazard extents (flooded areas) are determined by two approaches to form the hazard indicator, while land use, social vulnerability, transport systems, utilities and business settings are considered as exposure indicators. Finally, the potential risk is assessed by combining the hazard and exposure indicators into a single index, thereby allowing rapid comparison of coastal sectors' vulnerability. The study found that the main concentration of hotspots is in the town of Pomorie and its surroundings, while other candidates are scattered across the innermost Burgas bay.

Research paper thumbnail of Autoregresive (AR) bispectra of wind waves in the coastal zone

Comptes rendus de l’Acad´emie bulgare des Sciences, 2007

The paper examines the second-order non-linearity of the wind waves by bi-spectral analysis based... more The paper examines the second-order non-linearity of the wind waves by bi-spectral analysis based on non-parametric (conventional) and parametric approaches.
The parametric technique is presented by model that is in the class of auto-regressive
(AR) processes. The wave measurements are taken at depth 1.6 m in the coastal
zone of the Bulgarian part of the Black Sea. The bi-spectral estimates are evaluated
by aforementioned approaches and subsequently are compared in order to establish
whether AR modelling is applicable to analysis of the nonlinear wind waves propagating in the coastal zone. The results show good agreement between conventional
and parametric estimates.

Research paper thumbnail of Set-up and validation of a Delft-FEWS based coastal hazard forecasting system

Research paper thumbnail of GIS Hazard Maps - Bulgaria. In: Deliverable 5.1 - GIS-Based Hazard Maps. MICORE WP 5: Early Warning System

This chapter presents the GIS-based hazard maps that are set-up for the project area in Bulgaria.... more This chapter presents the GIS-based hazard maps that are set-up for the project area in Bulgaria. The maps have been compiled by Professor Fridtjof Nansen Institute of Oceanology - Bulgarian Academy of Sciences. The text herein represents an excerpt from Deliverable 5.1 GIS-Based Hazard Maps, WP 5: Early Warning System, project "Morphological Impacts and Coastal Risks Induced by Extreme Storm Events" (Acronym: MICORE), funded under the EU's 7FP, GA No 2002798.

Research paper thumbnail of Influence of Wave Climate on Intra and Inter-Annual Nearshore Bar Dynamics for a Sandy Beach

Geosciences, 2021

The study investigates cross-shore outer sand bar dynamics in an open-coast non-tidal beach at th... more The study investigates cross-shore outer sand bar dynamics in an open-coast non-tidal beach at the Bulgarian Black Sea due to wave climate. On seasonal to short-term (1–2 years) time scale, monthly field measurements of the outer bar profiles were related to respective modeled nearshore wave data. Hereby, seaward-shoreward bar migration was examined depending on the wave forcing, wave non-linearity, wave transformation scenarios, storms and direction of wave incidence. Analysis revealed that intra-annually highly non-linear waves were responsible for outer bar displacement, while the direction of migration depended on wave period, duration of conditions with wave steepness >0.04, angle of approach and total duration of storms. Short-term bar evolution was mainly governed by wave height and storms’ parameters as the angle of approach and duration. The correlation between the outer bar location and wave height annual variations initiated the first for the explored Black Sea region ...

Research paper thumbnail of Cultural Insights into Coastal Risks and Climate Change Resilience of a Society ‘in Transition’

G. Martinez (ed.), Culture and Climate Resilience, Palgrave Studies in Climate Resilient Societies, 2021

The study explores the cultural, socio-ecological, and institutional factors responsible for the ... more The study explores the cultural, socio-ecological, and institutional factors responsible for the present ways of handling natural hazards and coping with climate change challenges in Varna, a coastal city situated on the western Black Sea, Bulgaria. Diving into cultural perceptions of risk, governmental, social, and economic circumstances triggered after the political changes in 1989, and present state of development and implementation of disaster risk reduction, coastal management and climate adaptation legislation framework helped to reveal the main reasons behind the relatively low adaptive capacity and climate resilience of Varna.

Research paper thumbnail of Assessment of Coastal Receptors’ Exposure Vulnerability to Flood Hazard Along Varna Regional Coast

Coastal Engineering Proceedings, 2017

Storms and related disasters are phenomena producing coastal hazards and endangering human life a... more Storms and related disasters are phenomena producing coastal hazards and endangering human life and occupation. The study evaluates coastal receptors’ exposure and their vulnerability to storm-induced flooding hazard along Varna regional coast in Western Black Sea, Bulgaria. The assessment is performed employing the Coastal Risk Assessment Framework (CRAF) developed within EU FP7 RISC-KIT project. It constitutes a screening process that allows determination of susceptible alongshore sectors (hotspots) by assessing relevant hazard intensities, hazard extents and potential receptors’ exposure vulnerability within them by means of coastal indices approach. The ultimate goal is to evaluate potential risk posed by flooding in support to coastal managers, decision and policy makers. Assessment of coastal receptors’ exposure vulnerability is done by exposure indicators approach, using hazard intensities and flooding extents relevant to return period of 100 years. The approach consists of c...

Research paper thumbnail of Prototype of Early Warning System for Coastal Storm Hazard (Bulgarian Black Sea Coast)

Comptes rendus de l'Académie bulgare des sciences: sciences mathématiques et naturelles

Recent natural disasters in coastal areas have highlighted the devastating effects that hazards o... more Recent natural disasters in coastal areas have highlighted the devastating effects that hazards of marine origin can cause. This problem is addressed by set up of an on-line Early Warning System (EWS) for reliable prediction of morphological impacts due to marine storm events in support to civil protection strategies. The system involves a train of hydro- and morphodynamic models, predicting the storm impact on the beach, and a set of indicators, which convert model results in terms of key physical parameters to adequate warnings and series of actions to be undertaken by responsible authorities. The prototype consists of five interconnected key modules and lays the foundation for a greater national scale roll-out by adopting the following principles: using a generic structure adaptable to a range of different coastal environments; using free and open-source software; and tailoring the functionality of the EWS to the needs of end-users.

Research paper thumbnail of A physical model of wind waves in the coastal zone

Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE, 2008

ABSTRACT The variability of the amplitude-frequency structure of wind waves in space and time dur... more ABSTRACT The variability of the amplitude-frequency structure of wind waves in space and time during their transformation in the coastal zone are considered. Wave time series, measured synchronously in 15 points along the wave propagation, obtained at field and laboratory experiments, were used for the analysis. Free surface elevation time series were represented as a sum of first and second harmonics with amplitudes slowly varying in time (or envelopes of the waves of corresponding frequency bands). Relative changes of these amplitudes in space and time were studied also. It was revealed, that at the initial stage of the wave transformation, the changes of amplitudes of the first and the second harmonics are similar and amplitudes of the second harmonics are proportional to the squared amplitudes of the first harmonics. At this stage the variability of parameters of individual irregular waves can be explained by Stokes theory. Nearer to the coast the instantaneous values of the amplitudes of the first and the second harmonics varies in time chaotically and is not possible to construct a simple model of the variability of the parameters of individual irregular waves. The main reason for this effect is the backward energy transfer from the second to the first harmonics of the waves during nearly resonant non-linear triad interactions.

Research paper thumbnail of Spatio-temporal variability of the amplitude-phase structure of storm waves in the coastal zone of the sea

Oceanology, 2009

ABSTRACT The spatio-temporal variability of individual storm waves in the coastal zone is studied... more ABSTRACT The spatio-temporal variability of individual storm waves in the coastal zone is studied. Wave chronograms were presented as sums of the first and second harmonics with amplitudes slowly varying in time, which are envelopes for the waves of the corresponding frequency bands. The amplitude-frequency structure of individual waves was estimated from the variations in the amplitude of the envelopes. Bi-spectral analysis was applied to estimate the phase composition of the waves. It is shown that, in the initial stage of transformation, the fluctuations of the waves of the first and second harmonics are synchronous. The amplitudes of the second harmonics are proportional to the squared amplitudes of the first harmonics. Thus, a simple model is possible for the description of individual waves based, for example, on the generalization of the Stokes theory. As the waves approach the coast, the ratio of the amplitudes of the first and second harmonics in individual waves varies in time chaotically, thus it is not possible to describe individual waves on the basis of a simple model. The main cause of the chaotic variation of the amplitudes is the backward transfer of energy from the highest harmonics to the first harmonics due to the sub-near resonant triad interaction close to the resonance. The phase composition of individual waves depends on the distance propagated by the waves and on the stage (main or backward) of the energy exchange between the nonlinear harmonics.

Research paper thumbnail of Scenarios of nonlinear wave transformation in the coastal zone

Oceanology, 2013

ABSTRACT On the basis of field experiments and numerical modeling, we show that coastal zones are... more ABSTRACT On the basis of field experiments and numerical modeling, we show that coastal zones are classifiable according to manifestations of wind wave nonlinearity, which herein is recognized as periodic energy exchange between the first and second nonlinear wave harmonics depending on the average bottom slope and the Iribarren and Ursell numbers. The results offer a basis for developing vulnerability criteria for the coastal zone taking into account its nonlinear dynamics.

Research paper thumbnail of Past and recent trends in the western Black Sea storminess

Natural Hazards and Earth System Science, 2012

Research paper thumbnail of Critical storm thresholds for morphological changes in the western Black Sea coastal zone

Research paper thumbnail of Measurements and Analysis of Storm Induced Short-Term Morphological Changes in the Western Black Sea

The coastal morphology is highly sensitive to storm-induced impacts. All components of the coasta... more The coastal morphology is highly sensitive to storm-induced impacts. All components of the coastal system-aerial beach and dunes, submerged beach, nearshore bars–undergo changes during an extreme storm event (Sallenger et al., 1985; Morton and Sallenger, ...

Research paper thumbnail of Validation of the WAMC4 wave model for the Black Sea

Coastal Engineering, 2008

Research paper thumbnail of Probability distributions of peaks, troughs and heights of wind waves measured in the black sea coastal zone

Coastal Engineering, 2005

The present paper examines the adequacy of different probability density functions to describe th... more The present paper examines the adequacy of different probability density functions to describe the peaks, troughs and peak-to-trough excursions of wind waves measured in the coastal zone of the Bulgarian part of the Black sea. For that purpose various theories for non-Gaussian random process are applied. Some theories depend on the mean, variance and coefficient of skewness γ3 of the process. Others also take the coefficient of kurtosis γ4 into consideration. The analyzed field data are gathered in the coastal zone of the Bulgarian part of the Black sea with depth decreasing from 18 to 1.3 m. The measurements are carried out simultaneously for 11 points with time series of 20 min duration. The coefficients of skewness and kurtosis in those time series are expressed as functions of depth and spectral peak frequency. Analogous dependencies on depth of other parameters are also found. As a result of the investigation it is concluded that the probabilities of occurrence of large wave crests and heights are underpredicted by all of the theories considered.

Research paper thumbnail of Assessment of coastal receptors’ vulnerability to flood hazard along Varna regional coast

Coastal Engineering Proceedings, 2017

Storms and related disasters are phenomena producing coastal hazards and endangering human life a... more Storms and related disasters are phenomena producing coastal hazards and endangering human life and occupation. The study evaluates coastal receptors' exposure and their vulnerability to storm-induced flooding hazard along Varna regional coast in Western Black Sea, Bulgaria. The assessment is performed employing the Coastal Risk Assessment Framework (CRAF) developed within EU FP7 RISC-KIT project. It constitutes a screening process that allows determination of susceptible alongshore sectors (hotspots) by assessing relevant hazard intensities, hazard extents and potential receptors' exposure vulnerability within them by means of coastal indices approach. The ultimate goal is to evaluate potential risk posed by flooding in support to coastal managers, decision and policy makers. Assessment of coastal receptors' exposure vulnerability is done by exposure indicators approach, using hazard intensities and flooding extents relevant to return period of 100 years. The approach consists of combining several indicators into a single index, thereby allowing a rapid comparison of coastal sectors. Five types of receptors are considered to formulate the relevant exposure indicators: Land Use, Population, Transport, Utilities and Business, which subsequently are combined into an Overall Exposure Indicator to evaluate potential direct and indirect impacts. Results show that the most vulnerable to coastal flooding in terms of exposure are coastal sectors located within Varna Bay, comprising port and industry facilities with regional, national and international significance.

Research paper thumbnail of Identification of Coastal Flooding Hotspots in a Large Bay Using an Index-Based Risk Assessment Approach

N. Dobrinkova and O. Nikolov (Eds.): EnviroRISKs 2022, LNNS 638, pp. 1–15, 2023

The study aims to assess in probabilistic terms the magnitude of storminduced flooding hazard and... more The study aims to assess in probabilistic terms the magnitude of storminduced flooding hazard and vulnerability along Burgas regional coast (Bulgaria, western Black Sea) and to identify susceptible coastal sectors (hotspots). It employs the Coastal Risk Assessment Framework-a screening process that allows estimation of hazar'1d intensities, extents and potential receptors' exposure vulnerability within predefined sectors. Total water level, consisting of maximum wave run-up estimated using empirical models relevant for sandy beaches, artificial or rocky coastal slopes and storm surge level, is considered for calculation AQ1 of coastal flooding hazard. Furthermore, hazard extents (flooded areas) are determined by two approaches to form the hazard indicator, while land use, social vulnerability, transport systems, utilities and business settings are considered as exposure indicators. Finally, the potential risk is assessed by combining the hazard and exposure indicators into a single index, thereby allowing rapid comparison of coastal sectors' vulnerability. The study found that the main concentration of hotspots is in the town of Pomorie and its surroundings, while other candidates are scattered across the innermost Burgas bay.