In Bulgaria, the beach-dune systems are a valuable recreational resource and the most frequent landforms created in coastal depositional environments, making their preservation crucial. The accumulative forms comprise more than 70 beaches along the Bulgarian coast, including a total of 19 beach-dune systems (Stancheva 2010; Stanchev et al. 2013). They are prevalent along the southern Bulgarian Black Sea coast (Popov and Mishev 1974), but this information will be updated in the study presented herein. Most of the beach-forming substrates along the coast of Bulgaria are of terrigenous origin. Once eroded from the nearby coastal source areas, they are subsequently transported by rivers and surface streams and eventually deposited and redistributed in the littoral zone. As a result, estuaries, lagoons, inlets, bays, gullies and ravines are essentially linked to the spatial distribution of beach-dune systems. Furthermore, due to overlapping characteristics of the coastal morphodynamics (sand strips) and the aeolian transport (dunes), beach-dune systems are characterised by rather intense spatio-temporal variations (Popov and Mishev 1974; Krastev 2002; Keremedchiev and Cherneva 2003; Peychev 2004; Stancheva 2010; Stancheva et al. 2011; Kotsev et al. 2020; Prodanov et al. 2021b etc.).

Coastal landforms differ as to the degree of influence by morphodynamic processes that predominate in the littoral zone. They also exhibit notable differences in terms of their origin. However, in recent years, the anthropogenic activity or anthropogenic load has become yet another significant factor regarding coastal change (Stancheva et al. 2011; Stanchev et al. 2013; MSPRB 2021; UASME 2021), which applies with full force to the dune fields: Nessebar (Stancheva et al. 2011) and campsites, for example, Kavatsi, Smokinya, Gradina etc. (Stancheva 2010; MSPRB 2021). Over the years, dunes along the Bulgarian coast have been relatively understudied in geomorphological, morphodynamic (Passports of the Bulgarian Beaches 1994; Kenderova et al. 1999; Prodanov et al. 2019a, 2020b, 2021a; Kotsev et. 2020; Prodanov 2023) and geological aspects (Petrov 2013; Valchev 2014, 2015; Sinnyovsky and Sinnyovska 2016, 2017) or as Natura 2000 Habitats. Dunes of the first row at the back of a beach’s active portion are termed foredunes (corresponding to the so-called embryonic and mobile/white dunes) (Tzonev 2015a, 2015b), while these located further landwards are known as stabilised (grey) dunes, which may also be covered by arboreal vegetation (vegetated dunes) (Gussev and Tzonev 2015; Tzonev 2015c, 2015d). The negative, often moist depressions located amongst dune ridges are termed dune slacks (Tzonev 2015d). Gussev and Tzonev (2015) summarize that a substantial part of the Bulgarian coastal dune areas is included in the Natura 2000 Network: 58% of embryonic dunes (ED), 73% of white (shifting) dunes (WSD), 89% of grey (fixed) dunes (GD), 100% of wooded dunes (WD) and 67% of humid dune slacks (HDS). In recent years, an increase in non-psammophytes, grass and shrubland species has been observed, probably due to tourist activity and technogenic pressure, which should be addressed as an issue in the future (Valcheva et al. 2019, 2020, 2021).

Redistribution and accumulation of sand through aeolian transport represent the essence of dune formation. Dune locations are indivisibly related to the beach exposure towards the prevailing strong winds direction. For the BBSC, threshold values for aeolian transport are assumed to be 15 m/s (Popov and Mishev 1974). The prevailing eastern and north-eastern winds are of utmost significance, although such coming from the west quarter are also important concerning aeolian transport and subsequent dune formation. Аt beaches open towards the east and prevailing strong north-easterly winds, dunes form in the middle, especially in the southern section of the beaches. Accordingly, at sand strips exposed towards the north, dunes are formed in the middle and western beach sections (Popov and Mishev 1974).

At the end of the 1970s, IO-BAS carried out the first scientific studies on the BBSC for mapping the beach-dune systems. For a decade, in-situ campaigns were carried out to map all sand beaches and coastal dunes (as landforms) and determine their morphodynamic properties. Unfortunately, the results of these studies were kept confidential during Bulgaria’s socialist period and, currently, only the beach and dune locations are available in the IO-BAS archives. After 1991, at the beginning of the democratic period, IO-BAS resumed systematic studies of the Bulgarian coast. The most detailed records of beach-dune systems on the BBSC date from that time (Passports of the Bulgarian Beaches 1994).

The webGIS-based information system for cadastral data and services - CAIS comprises several components containing and visualising thematic geospatial data, amongst which is a module dedicated to coastal features (i.e. beaches, dunes, estuaries, lagoons, wetlands, coastal protection infrastructure etc.), as listed in Article 6, paragraphs 4 and 5 of the Black Sea Coast Spatial Development Act (BSCSD 2008). However, despite being a highly valuable (and openly available) data source, the cited thematic module of CAIS fails to represent the up-to-date locations and boundaries of all the above-mentioned coastal features. Amongst the reasons for these drawbacks are certain peculiarities of data updates on behalf of the GCCA, cadastral parcel-based approach in delineating contours of the cited features, discrepancies in the coastal classifications used, delayed in-situ surveys on behalf of the authorities in charge, resulting property rights issues due to the legal status of the cited coastal features etc.

The use of drones for photogrammetric surveys is widespread in studies of beach-dune systems around the world (Papakonstantinou et al. 2016; Suo et al. 2017; Laporte-Fauret et al. 2020, 2022; Fabbri et al. 2021). In the last five years, drones have become the most efficient and inexpensive method for environmental monitoring, habitat and vegetation mapping and analysis of geomorphic processes/changes (Turner et al. 2016; Choi et al. 2017; Madurapperuma et al. 2018; Guisado-Pintado et al. 2019; Pagán et al. 2019; Prodanov et al. 2019a, 2019b; Suo et al. 2019; Kotsev et al. 2020; Prodanov 2023). Scientific UAS surveys in Bulgaria are focused on the SfM-derived georeferenced data for different purposes, such as geomorphological or landscape mapping (Dimitrov and Savova 2019; Prodanov et al. 2019a, 2019b, 2021a, 2021b; Kotsev et al. 2020; Tcherkezova et al. 2020; Dinkov et al. 2021; Tcherkezova 2021; Trendafilova and Dechev 2021; Prodanov 2023), landslide processes (Atanasova and Nikolov 2021; Pashova et al. 2021; Nankin et al. 2022), geoarchaeological mapping (Peev and Prodanov 2020; Prahov et al. 2020; Tzvetkov 2020; Vajsov et al. 2020) etc. The cited references prove the wide range of digital results obtained, making drones a suitable mapping tool for beach-dune systems along the BBSC.

Since 2018, IO-BAS has been using Phantom 4 Pro, Phantom 4 RTK and WingtraOne drones (Figs 2, 3). As of June 2022, over 97% of the Bulgarian coast has been surveyed using these UAVs, excluding military areas and national security sites (Prodanov et al. 2020a etc.). Furthermore, geodetic GNSS surveys were performed to physically trace dune landforms in wooded areas (such as the Koral coastal area, town of Kiten) and to locate 2316 ground control points (GCPs) in order to increase the accuracy of the UAV photogrammetric measurements. In addition, photo verification of landforms and plant species within the range of beach-dune systems was performed at over a thousand locations (Figs 2, 3). Flight data were processed by specialised photogrammetric software, such as Agisoft Metashape, Pix4D and Global Mapper. The digital surface models (DSMs) were brought to the Baltic Height System. All vector and raster files representing survey results were combined into a coherent geodatabase, with WGS 1984/UTM zone 35N as a spatial reference.

Figure 3.

Example of field surveys and UAS mapping of coastal dune landforms using WingtraOne and DJI Phantom 4 RTK drones at Kavatsite-Smokini beach-dune system (Location on Fig. 4).

Sediment sampling was performed by the IO-BAS team within each beach-dune system along the BBSC. Samples were taken at 1632 stations between February 2018 and May 2022 along morpho-lithologic transects and distinct locations on the CDLs (Fig. 3). Sands were collected from the beach face, beach face crest, summer berm, high beach winter berm, seaward dune slope, the crest and lee slope of the primary dune, a transition zone between primary and secondary dunes, middle sections of secondary dunes and the end of the secondary dunes. Sediment characteristics were determined using a Mastersizer 3000 Laser Diffraction Particle Size Analyzer in the Laboratory of Lithodinamics and Sediment Analysis at IO-BAS. The study used a grain-size distribution and statistics package for the analysis of unconsolidated sediments by sieving and laser granulometry (Blott and Pye 2001). The sediment stations were classified according to the Wentworth grain-size scale (Wentworth 1922) and Gradistat (Blott and Pye 2001).

For CDLs, two main levels of hierarchical subordination were used. Primarily, they correspond to (I) beach-dune systems - they represent unified beach and dunes in a geomorphological sense often named on their localities (Fig. 4, Suppl. material 1). The secondary level is (II) beach-dune sectors compliant with the coastal thematic module of CAIS (Suppl. material 1).

Figure 4.

Spatial distribution of sand dune systems along the Bulgarian Black Sea coast.

The geomorphological field surveys were conducted systematically outside the tourist season and low level of anthropogenic influence on dunes. In the present study, the spatial distribution of CDLs was based on morphometric analyses of the DSMs, visual analyses of the OMs or 3D photorealistic models, as well as in situ verification. From a geomorphological point of view, the division of CDLs into primary (embryonic and foredunes) vs. secondary (blowouts, transgressive, parabolic, cliff-top, perched etc.) or fixed vs. mobile dunes is important for the study of land-sea interactions and coastal natural resources.

The vegetation field observation (verification) was conducted systematically in the summer (July -August) of 2021 and 2022. In the light of the Natura 2000 European ecological network and the EU Habitats Directive, the inventory of CDLs carried out and newly mapped dunes were classified according to their characteristics in the sense of the Red Data Book of Bulgaria (Tzonev 2015a, 2015b, 2015c, 2015d; Tzonev and Gussev 2015). Furthermore, field observation of the vegetation type and anthropogenic influence on the dunes was conducted within the active touristic period in the summer seasons of 2021 and 2022. As a result, the CDLs were divided into shifting/mobile dunes (embryonic and white dunes) and relatively stabilised dunes (fixed grey dunes, wooded dunes and humid dune slacks) - Suppl. material 1.

Four beach-dune systems have been identified and mapped along the northern Bulgarian coast: Durankulak, Krapets, Ezerets-Shabla and Bolata (Fig. 4, Suppl. material 1). Examples of well-formed primary and secondary dunes are observed in the Durankulak-North coastal sector. The first row represents foredunes of medium sand and the wide beach strip provides conditions for the formation of embryonic dunes. Secondary dunes in the section are flat-to-undulating sand sheets to sand sheets that rise in elevation downwind and end up in a slip face, for which we will use the term ramp dunes. After the construction of the Durankulak Fishing Port (Fig. 5), the geological conditions and the exposure of the coast to wind waves (Valchev et al. 2014) have contributed to the accumulation of a narrow beach and adjacent embryonic dunes have been formed (Fig. 4, Suppl. material 1).

Figure 5.

3D model of newly identified coastal sand dune landforms north of Durankulak Fishing Port from 2018 (see location on Fig. 4).

Dunes accumulated over barrier beaches attached to the land at both ends are characteristic of the Dobrudzha coast. Mobile white and stabilised grey dunes separate Durankulak, Ezerets and Shabla lakes from the Black Sea. The average width of the dune systems is approximately 60 m. South of Cape Shabla, the erosional morphology dominates. The coast consists of karstified rock platforms or vertical cliffs without sand beaches. A small sand-dune system exists in the area of Bolata Cove. The dunes are small in size and close to the shoreline (Prodanov et al. 2019b). Although they are protected by an old dilapidated military port, they have been subjected to high anthropogenic pressure and are almost completely destroyed. Sediment profiles show the presence of coarse sand in the active beach area, passing into medium sand within the primary and secondary dune areas. The finest sands occur at the end of the secondary dunes located immediately next to lakes or backwoods at Durankulak - North.

The Franga-Avren coast is also known as the Varna coastal region (Fig. 4). Coastal dune landforms were identified and mapped in the following sectors: Batova River Estuary, Zlatni Pyasatsi Panorama Resort (Fig. 6), Asparuhovo quarter (Varna) – Fig. 7 and Pasha Dere Ravine. South of the Batova River Estuary, the specific geological and geomorphological conditions do not allow the formation of long beach-dune systems. Most beaches are narrow and heavily altered by the thriving tourism along the Varna coast. Beaches have been exploited and groomed for many years, which does not allow the formation of dunes on them. In some places, small embryonic dunes were found that did not exceed the minimum mapping unit and were, therefore, not reflected in Suppl. material 1.

Figure 6.

Newly identified coastal sand dune landforms at Riviera Beach, Zlatni Pyasatsi Resort (A digital surface model B orthophotomosaic from 2022) - (see location on Fig. 4).

Figure 7.

Newly identified coastal sand dune landforms (embryonic, grey and wooded dunes) at Asparuhovo Beach in the southern part of Varna Bay (A digital surface model B orthophotomosaic from 2022) - (see location on Fig. 4).

In the second half of the 20^th century, a period of mass industrialisation, the Varna coast was heavily armoured by hydrotechnical facilities – groins, seawalls etc. To a large extent, these constructions have changed land-sea interactions. These help for dune formation at some urban and resort sectors of the Varna coast by the deposition of sea sand after the construction of the T-groins (Fig. 6) and Karantinata Fishing Port (Fig. 7). A few remnants of the large dune field separating Varna Lake from the Black Sea remained under the landscaped part of Asparuhovo District. South of Cape Galata, the development of embryonic dunes positioned in front of the Pasha Dere Ravine was reported.

Kamchiya coast is emblematic of the BBSC. The shoreline between Capes Paletsa and Karaburun is 12.9 km long, which makes Kamchiya-Shkorpilovtsi the longest beach on the Bulgarian coast. Over 90% of it is a well-formed beach-dune system with an area of 326 ha, comprising five different sectors: Kamchiya – North (Romantika Campsite), Kamchiya River Mouth, Kamchiya-South (Novo Oryahovo Village), Shkorpilovtsi and Shkorpilovtsi-South (Samotino Village). Dunes in the five sectors differ due to variations in the vegetation types, geological and geomorphological processes that affect them. North of the Kamchiya River mouth, low, up to 1–1.5 m high embryonic dunes were formed along the entire beachfront (Prodanov et al. 2021b). Immediately next to the river mouth, in a small area between the flood terrace and the road, stable wooded dunes are present (Fig. 4, Suppl. material 1). The low-lying relief is a precondition for the different nature of the dunes near the villages of Novo Oryahovo and Shkorpilovtsi. In some areas, the secondary (wooded) dunes reach up to 1 km inland, where the sand is still medium-grained. Along the flattened central dune fields, prevalence of grey dunes was established. Their stabilised sand ridges vary between 1.5 and 3 m in height. The foredunes are mainly white (mobile), at places armoured by embryonic mobile dunes of small size up to 25–40 cm high, formed by medium-grained sand.

Passing south from the mouth of the Fundakliyska River, the beach-dune system becomes narrower and the existing grey dunes are limited by a road that marks the northern border of the Balkan Mountains. This narrow strip is an example of misclassified dunes in CAIS. It is important to note that a wide strip of wooded dunes was recorded in the Shkorpilovtsi - South (Samotino) sector. During the field surveys in the Cape Karaburun direction, it was established that the narrow sand-dune system of embryonic and grey dunes passes over steep cliffs covered by cliff-top wooded dunes (Fig. 4, Suppl. material 1).

In this sector, there are steep flysch cliffs all along the shoreline with narrow beach strips at the cliff bases, formed mainly by eroded and abraded material. In the southern part, the cliff descends almost to sea level at the Hadzhiyska River Mouth and the low cliff sections between the towns of Nessebar and Aheloy. The depositional relief is represented by stable beach-dune systems at Kara Dere Ravine, the town of Byala, Irakli Protected Area, Slanchev Bryag (Sunny Beach) Resort and the town of Nessebar (Figs 4, 8, Suppl. material 1).

Figure 8.

Coastal sand dune systems at Slanchev Bryag Resort and Nessebar coastal sectors - embryonic dunes (ED), white (shifting) dunes (WSD), grey (fixed) dunes (GD), wooded dunes (WD) A UAV photogrammetric DSM from 2022 B UAV orthomosaic from 2022 (see location on Fig. 4).

Small embryonic dunes (0.287 ha) were identified and mapped during the field surveys. These dunes have formed after the construction of the Byala fishing port that has created a sheltered environment from the eastern storm processes, facilitating aeolian and deposition processes. Over the past three years, the dunes have progressively transitioned into white (shifting) dunes. It is important to pay attention to their preservation in the future, as they are in an area with strong anthropogenic pressure, such as fishing activities, boat launching etc. In Kara Dere, Vaya River Mouth and Irakli sectors, an extension of the embryonic dunes and some newly formed ones have been discovered (Fig. 4, Suppl. material 1).

The most significant beach-dune systems along central parts of BBSC are observed in the coastal sectors of Slanchev Bryag Resort and the town of Nessebar (Fig. 4, Suppl. material 1). The low-lying relief and abundance of sand material at Slanchev Bryag Resort are the main reasons for the presence of coastal dune landforms inside the resort complex. Over the years, many secondary dunes have been formed. Embryonic dunes, white (shifting) dunes, grey (fixed) dunes (GD) and wooded dunes (WD) with a total area of 46.98 ha were identified. The comparative spatio-temporal analysis of coastal dune dynamics showed that 14.80% of their area was subjected to strong anthropogenic pressure as a consequence of expanding tourism (Fig. 4, Suppl. material 1).

The Nessebar dunes are distributed between the Nessebar Sand Dune Field and Nessebar – South coastal segments (Fig. 8). Their area is almost twice as large as those of Slanchev Bryag. Again, the local geomorphological conditions are the leading factor in shaping out their modern boundaries. At the Nessebar Sand Dune field, dunes are 100% secondary, formed under conditions of intense aeolian transport in the past. The sediment nourishment of the Nessebar grey and wooded dunes nowadays is rather limited due to increased distance from the source province (the beach of Nessebar - South) as well as the presence of primary foredunes and vegetation cover posing an effective barrier to aeolian transport. Another coastal issue at the Nessebar Sand Dune Field in terms of sand nourishment is the urbanisation and large-scale development of the Mladost residential area of Nessebar in the 1960s that altered the wind flow from the north side of the dunes at Slanchev Bryag - South and the associated aeolian sand transport (Fig. 4, Suppl. material 1).

Pomoriyska Sand Spit, Pomorie, Sarafovo, Burgas (Central), Burgas (South), Kraymorie, Vromos and Chernomorets beach-dune systems have been identified and the dunes on Atanasovka Sand Spit were mapped for the first time (Fig. 4, Suppl. material 1). Over the years, numerous factors have had an impact on the coastal spatial pattern of Burgas and Pomorie Bays. Similar to Durankulak Lake, Pomoriysko and Atanasovsko Lakes are separated from the sea by sand strips known as Pomoriiska and Atanasovska sand spits. Geomorphologically, they also represent barrier beaches attached to land at both ends and covered with well-formed foredunes with a maximum height of 3.7 m (Suppl. material 1). Over the years of development, the sand spits have been colonised by specific psammophilous species characteristic of grey dunes, for example, sand cornflower (Centaurea arenaria M.Bieb. ex Willd.), white-stemmed musk (Jurinea albicaulis subsp. kilaea (Azn.) Kožuharov), Euxinian campion (Silene euxina (Rupr.) Hand.-Mazz.), milkweed (Cionura erecta (L.) Griseb.) etc. (Tzonev 2015c). In the Sarafovo beach-dune system, grey dunes also predominate over white ones. Dunes composed of medium-grained sand have been developing unhindered within the Burgas (Central) Beach for many years. Although moderately exposed to wave action (Valchev et al. 2014), positive sediment balance and weak, but constant accretion have contributed to the formation of mobile embryonic and white dunes (Fig. 9, Suppl. material 1). Our research team mapped these dune landforms for the first time at the beginning of 2022. Unfortunately, as of October 2022, they still do not appear in the thematic coastal module of CAIS, necessitating an immediate update of the relevant coastal geodatabase of GCCA.

Figure 9.

Newly identified coastal dune system at Burgas (Central) Beach - embryonic dunes (ED), grey (fixed) dunes (GD) A UAV photogrammetric DSM from 2022 B UAV orthomosaic from 2022 (see location on Fig. 4).

Strong anthropogenic pressure on these dune systems was registered in the last years of field surveys. South of the City of Burgas, the dunes undergo even more significant human alterations, affecting up to 65–70% of their area in the Burgas (South) and Burgas (Pobeda quarter) depositional sectors (Fig. 4, Suppl. material 1). The permanently lost beach-dune systems were established along the Burgas coast: Pomorie (East), Europa Campsite, Lahana-West, Lahana-East and Rosenets (West) at Cape Chukalya (Fig. 4).

The largest number of beach-dune systems (25) have been identified along the Medni Rid - Strandzha coast. Out of 157 km of shoreline between the town of Chernomorets to the north and the Village of Rezovo to the south, approximately 32 km represent depositional relief comprising the following beach-dune systems: Gradina Campsite (Sozopol Bay), Sozopol, Harmani and Kavatsite-Smokini Beaches (Fig. 10), Alepu and Arkutino Lagoons (Fig. 11), Ropotamo River mouth, Primorsko (Stamopolu – Perla Beach), Primorsko – South Beach, Atliman Bay, Kiten, Koral Beach and Yug Campsite, Lozenets, Oasis, Arapya, Tsarevo (Popski plazh), Nestinarka and Ahtopol Beaches, Veleka and Butamyata River mouths (Fig. 12), Lipite and Listi Beaches, Silistar River mouth and Rezovo-Kastrich Beach (Suppl. material 1). Generally, the systems consist of well-formed primary dunes, including foredunes and incipient dunes. Usually, the first row is represented by 7–9 m in high white/grey dunes and armoured by embryonic dunes (Kavatsite, Smokini, Arkutino etc.). In rare cases, as at Butamyata Beach, the dune field is further shaped out by the small estuary. However, in the last ten years, dunes have evolved from small embryonic to grey ones and occupy a much larger portion of the beach. Unfortunately, this beach-dune system has been systematically destroyed every year by excavation, trampling and grooming as part of the beach preparation for the summer season because a significant portion of them is not reflected in the coastal thematic module of CAIS. In this sense, the Kavatsi Dune Area is an example of strong anthropogenic pressure on the dunes (Valcheva et al. 2022). Therefore, an urgent update is required of the relevant geodatabase of GCCA in order to protect them (Suppl. material 1).

Figure 10.

Coastal sand dune systems at Kavatsite Beach, Sozopol - embryonic dunes (ED), white (shifting) dunes (WSD), grey (fixed) dunes (GD) and wooden dunes (WD); A spatial distribution of beach-dune systems in 1918 (Aerial Photomosaics 1918) B UAS orthomosaic from 2022.

Figure 11.

А an aerial view of the Arkutino beach-dune system from 2022 (photography of Dr. Bogdan Prodanov) B UAV digital surface model of the Arkutino sector with the second highest positioned coastal dunes (50.2 m a.s.l.) along the Bulgarian coast from 2022 (see location on Fig. 4).

Figure 12.

Coastal sand dune system at Butamyata Beach (Sinemorets) - embryonic dunes (ED) and grey (fixed) dunes (GD) A UAV photogrammetric digital surface model from 2022 B UAV orthomosaic from 2022 (see location on Fig. 4).

The highest positioned coastal dunes along the Bulgarian coast were registered at the perched Sozopol Sand Dunes (grey dunes), located at Sozopol Hill at an impressive height of 61 m above sea level in coordinates: 42°24'16.5907"N, 27°42'00.0501"E (Fig. 10). It is noteworthy to mention that, in the past, prior to the high level of anthropogenic impact on the Sozopol Hill and Budzhaka Locality, these dunes have been nourished with sand through aeolian transport from two sources simultaneously - the Harmanite Beach (from the northern direction) and the Kavatsite Beach (from the southern direction) (Fig. 10, Suppl. material 1). The Sozopol cliff-top dunes have been formed by wind activity, which has transported medium to fine sand from the aforementioned beaches. However, over the last two decades, construction activities in the northern part of Kavatsi and the southern part of Harmani have discontinued the supply of sand to this secondary dune system (Fig. 10A). These dunes have had a chance to remain relatively undisturbed from human intervention, allowing for the colonisation and stabilisation of psammophyte vegetation on their sandy surfaces. The sediment analysis of seven stations taken within these dunes exhibits an extremely poor sorting, indicating a low intensity of morphodynamic processes of the dune sand at this hypsometric level.

The second highest positioned dunes were registered in Arkutino coastal sector. The system is composed of a long row of frontal dunes, discontinued by small-size blowouts, followed inland by mosaics of parabolic and cliff-top dunes, which reach a height of 50.2 m a.s.l at coordinates: 42°19'32.6673"N, 27°44'10.2816"E (Fig. 11). In many sections of the Medni Rid - Strandzha coast, the embryonic dunes have been colonised by psammophytes that are characteristic of white dunes, slowly increasing their area. As a result, 63% of the dunes are stabilised and, over the years, together with the wooded dunes, have preserved their area of 45 ha (12%). Most beach-dune systems consist of secondary dunes. They were classified as parabolic and cliff-top dunes, blowouts, sand sheets (dune fields) that rise in elevation downwind and end up as a slip face (Arkutino, the Sozopol Sand Dune Area etc.).