RECONSTRUCTING RECENT BEACH MORPHOLOGICAL CHANGES BY REPEAT PHOTOGRAPHY-EXAMPLE OF ZOGON BEACH ON THE ISLAND OF HVAR ( CENTRAL ADRIATIC )

U radu je analiziran geomorfološki sustav koji čine jaruga i žalo Zogon na otoku Hvaru s ciljem diferenciranja prirodnih i antropogenih procesa koji utječu na promjene žala. Primjenom metoda ponovljene fotografije, orto-foto snimaka i terenskog kartiranja ustanovljeno je da se u razdoblju od 60-ih godina 20. stoljeća do danas površina žala Zogon smanjila za oko 50 %. Smanjenje žala može se povezati s recentnim antropogenim djelatnostima na širem području istraživanja, osobito višestrukim nasipavanjem korita jaruge prilikom gradnje te manjim promjenama u korištenju zemljišta i prirodnom regeneracijom vegetacije što uzrokuje smanjenje dohrane žala. S druge strane, preokret u evoluciji žala u promatranom razdoblju, koje je po definiciji akumulacijski reljefni oblik, iz akumulacijskog ili stanja ravnoteže u stanje dominantne erozije možemo povezati s recentnim klimatskim promjenama i izdizanjem relativne morske razine. KLJUČNE RIJEČI: žalo, jaruga, obalna geomorfologija, promjene zemljišnog pokrova, promjene korištenja zemljišta, klimatske promjene, vinogradarstvo, Sveta Nedjelja


INTRODUCTION
Recent climate changes are an important issue today and therefore also a frequent research topic.They are best observed in areas which people know well, or in areas where there are visual records from previous years such as photographs, footages, landscape pictures etc. Numerous changes can be observed today along the eastern Adriatic coast e.g.ice melting in mountainous speleological objects (Ledenica in Štirovača, Boi et al., 2012), sea level rise (Faivre et al., 2013;Faivre, Butorac, in press), floods as a result of precipitation extremes (Abdulaj et al., 2014;Gaji-Čapka, Cindri, 2014), frequent gullying (Faivre et al., 2011), frequent storms and storm surges (Meugorac et al., 2015), activation of landslides (Faivre et al., 2013;Mihali et al., 2017) and many others.
Changes can be first and best observed along the coast, where land and marine environment intertwine.Therefore, the coasts are key geographical areas today, as they lie at the of climate change (Kaniewski et al., 2016).The coast represents a dynamic geomorphological system that connects processes in the sea with those on land.Onshore processes, although outside the coastal zone, can have a significant impact on understanding coastal changes.One of the most dynamic coastal relief forms is a beach.Namely, only 20% of global beaches show relative stability today, while the other 80% are in constant change.The tendency of most of today's beaches is erosion (70%), while only 10% of world beaches are growing (Bird, 2008).
Beaches represent very attractive zones from a tourist point of view.There has been an increasing demand for them in recent years due to the development of bathing tourism.So, anthropogenic interventions on the beaches are becoming more and more frequent.Consequently, the understanding of geomorphological changes on the coast is becoming even more important for sustainable management of coastal resources (Woodroffe, 2002).
Zbog specifičnih geomorfoloških obilježja, žala je poželjno proučavati zasebno u krupnom mjerilu (Pikelj, Jurai, 2013.).Tako je predmet istraživanja ovoga rada žalo Zogon u Svetoj Nedjelji na otoku Hvaru.Žalo Zogon nastalo je s jedne strane procesima jaruženja te s druge strane, unazadnom (regresivnom) erozijom kvartarnih breča u kojima je žalo i oblikovano.U radu će se analizirati više desetljetne promjene žala od 60-ih godina 20.stoljeća do danas.Provest će se geomorfološka procjena promjene žala u razdoblju od oko šezdeset godina primjenom metode ponovljene fotografije koristeći geografski informacijski sustav (GIS), kartiranje uz pomoć GPS-a, te georeferenciranih orto-foto snimaka iz 1968.i 2011.godine.Raz-flysch (Pikelj, Jurai, 2013).Consequently, most of the beaches were formed in carbonate material.Even if there are different kind of beaches along the eastern Adriatic coast (see e.g.Pikelj, Jurai, 2013;Marriner et al., 2014;Ruži et al., 2014), a large number of beaches is formed in proluvial material of small valleys and gullies (ravines) (Jurai et al., 2009;Faivre et al., 2011;Ruži et al., 2011).The occasional streams bring the material out of the drainage basin and create fans in which the beaches are formed in the contact with the sea.Therefore, as usual in temperate zones, the beach material is primarily composed of sediments of terrigenous origin (Pirazzoli, 1993).Thus, morphological properties of beaches along the eastern Adriatic coast relay on the supply of terrigenous material as a result of weathering, gullying, slope-wash erosion, rockfall and rockslide, and on the impact of the sea on that material.The position and orientation of beaches in relation to the dominant wave direction as well as the morphology of the shoreline are of utmost importance in defining morphodynamic characteristics of a particular beach.However, a very important factor of beach morphology is also the dynamics of gullying, which is becoming more and more intense and more frequent, and thus greatly affects the morphology of many beaches (e.g.Faivre et al., 2011).
Geomorphological changes of beaches along the eastern Adriatic coast on different spatial and temporal scales is a research topic which rises a lot of interest today (e.g.Raji et al., 2010;Benac et al., 2010;Faivre et al., 2011;Ruži et al., 2011;Pikelj et al., 2014;Pikelj et al., 2015;Lonar et al., 2016;Ruži et al., 2017).Such surveys enable the observation of recent geomorphological changes of beaches and their association with anthropogenic activities.
Due to their specific geomorphologic characteristics, it is preferable to study each beach separately and on a small scale (Pikelj, Jurai, 2013).This research focuses on the Zogon beach at Sveta Nedjelja on the Island of Hvar.Zogon beach was created by the processes of gullying, on one hand and, on the other hand, by the regressive erosion of Quaternary breccia in which the beach was shaped.In this paper, decadal changes of the beach morphology from motrit će se i antropogeni utjecaji, odnosno načini na koje ljudske djelatnosti utječu na žalo (promjene u korištenju zemljišta i građevinski zahvati).Nepostojanje točnih zapisa inženjerskih radova često otežava odvajanje prirodnih procesa od antropogenih utjecaja.

PODRUČJE ISTRAŽIVANJA
Hvar je najduži hrvatski otok s duljinom od 67,8 km, četvrti po veličini s površinom od 297,4 km 2 (Duplani Leder i dr., 2004.).Zapadni dio the 1960s in the last century till the present days were analysed.The geomorphological assessment of beach morphological change was conducted for the period of about 60 years based on the method of repeat photography using Geographic Information System (GIS), GPS mapping, and georeferenced ortho-photos from 1968 and 2011.Anthropogenic impacts, that is the ways in which human activity affects the beach (changes in land use and construction works) will be considered.The lack of accurate records on engineering works makes the separation between natural processes and anthropogenic influences rather difficult.

RESEARCH AREA
Hvar is the longest Croatian island with a length of 67.8 km, and the fourth in size with a surface of 297.4 km 2 (Duplani Leder et al., 2004).The western part of the island reaches the width of 10 km while the eastern part is only 2,5 km wide.The coastline is 254.2 km long with the indentation coefficient of 4.14.Following the Island of Dugi otok it is the most indented island of Croatia (Bognar, 1990).The Island of Hvar belongs to the group of Central Dalmatian islands specific by its west-east spreading direction.As this spreading direction is most prominent on Island of Hvar, the whole group of islands is named "Island of Hvar group" (Rogli, 1977).The maximum sea depth around the Island of Hvar reaches 87 m in the Hvar Channel in the north and 63 m in the south in the Korčula Channel.Zogon beach is located on the southern coast of the island, at the foot of the highest peak of Island of Hvar (Sv.Nikola -628 m) in Sveta Nedjelja (Fig. 1).

GEOLOGICAL AND GEOMORPHOLOGICAL PROPERTIES
Island of Hvar is composed mainly of rocks that were created by deposition in the shallow sea as part of the former Mesozoic carbonate platform (Marini, 1995;Vlahovi, et al., 2005).Generally, the island represents a large overturned anticline composed of Cretaceous rocks thrust along the southernmost part of the island over the Middle Eocene deep-water sandstones and marls (Fig. 2) (Marini, Majcen, 1976).
The oldest outcrops belong to the lower Cretaceous and they are located in the western part of the island, in the area of Pitve, Vrisnik, Svirče, Selce and Velo Grablje.Those are brownish well-layered dolomites with scarce interlayers and thin lenses of limestone as well as well-layered limestones around 200 m thick (Herak et al., 1976;Borovi et al., 1977).
U okviru kvartarnih sedimenata također su zastu-well-layered brownish limestones continue.On the peripheral parts of the limbs of the main island anti-form there are also layered bulky rudistic limestones about 600 m thick.Those are light brown and white limestones with thin dolomite lenses (Herak et al., 1976).Palaeogene sediments are deposited above the karstified surface of Cretaceous rocks with some pockets of bauxite.They can be found only in the area between Hvar and Milna, Zaraće, around Zavala and near the coast of Sveta Nedjelja.Palaeogene deposits are composed of foraminiferal limestones, transitional marls and deep-water sandstones and marls (Paveli et al., 2011).Palaeogene flysch is of great importance for island population as it constitutes a good agricultural base (fertile soil) (Rogli, 1977).
Quaternary deposits can be found on the northern side of the island (Fig. 2.) on the area of the polje of Stari grad, Vrbanj, Jelsa and Vrboska, and on the southern side on the area of Zavala and Sveta Nedjelja (Marini, Majcen, 1976;Markovi-Marjanovi, 1976;Bognar, 1990).
Colluvial deposits are represented with slope
Na otoku dominira krški i fluviokrški reljef, a oblik otoka i veliki nagibi pogodovali su aktiviranju brojnih geomorfoloških procesa.Fluviodenudacijski i akumulacijski procesi ističu se na sjever-breccia which is mainly present on the southern slope of Island of Hvar near Sveta Nedjelja and Zavala.On the Island of Hvar three generations of talus breccia can be distinguished: 1) red scree cones breccia formed of limestone and dolomite consolidated by terra rossa, 2) scree cones breccia formed of not rounded limestones and dolomite consolidated with loess material, and the 3) youngest scree cones breccia located on the highest and steepest parts of Island of Hvar (Markovi-Marjanovi, 1976).
Quaternary sediments also includes aeolian (Paveli et al., 2011), alluvial and proluvial sediments (Bognar, 1990).Proluvial fans are found especially in the area between Sv.Nedjelja and Zavala, in whose material, beaches have been shaped, while alluvial sediments are most common in the Starigradsko polje and in the area of Jelsa and Pitve (Bognar, 1990).
The highest elevations above 500 m are located in the central part of the island where the highest peak (St.Nikola) is located.The island can be divided into the southern and northern side along the major ridge.All six categories of slope inclination are present on Island of Hvar (Bognar, 1990).The highest slopes are found at the foot of the ridge and on the sea cliffs (< 55°), while the smallest appear in the polje of Starigrad and the levelled area of the hilly part Rudine -Kabal (> 2°) with the exception of the steeper slopes of Kabal (5-12°) (Miunovi, 2017).
Karstic and fluviokarstic forms dominate on the island.The shape of the island and steep slopes favoured the activation of numerous geomorphological processes.Fluvio-denudational and accumulation processes are prominent on the northern side of the island near Jelsa and Dol.They are related to the occasional flows which form small valleys.Slope processes are widespread but their intensity is much more important on steep slopes formed mainly in dolomites which are mechanically more susceptible to weathering than limestones.The most commonly occurring processes are rockslide, rockfall, slope-wash erosion and gullying, which primarily form scree cones and fans.Gullying is most intense on the southern side of the island.In the vicinity of Zavala there is the largest number of gullies, even 9-10 on km 2 (Bognar, 1990).On the confluence of gullies with the sea proluvial fans are formed.In the eastern part of the island karrens are widespread.Shallow dolines (Bognar, 1990) and speleological objects can be also found.Fluviokarst relief is represented with erosional plains and numerous dray valleys on the northern slope of the island (Markovi-Marjanovi, 1976;Bognar, 1990).
On the southern shores of Island of Hvar, westward from Hvar town and Sv.Nedjelja, structurally predisposed cliffs are the most prominent features.As those are plunging cliffs, the influence of waves is negligible.At the same time it should be noted that today's Adriatic coast is relatively young (Benac, Jurai, 1998;Faivre, Fouache, 2003;Suri, 2009).
Looking at the island as a whole, low sloping rocky coasts formed in monoclinal and horizontal layers are the most widespread.The low sloping shores formed in clastic sediments are significantly less present (Bognar, 1990) and represent an ex-
S obzirom na reljef i njegovu izduženost na tremely small part of the total length of the coast of Island of Hvar.The gully at the studied area is formed in dolomites of the Cretaceous period while the Zogon beach is formed in Quaternary breccia at the contact with Eocene marls along the thrust front (Fig. 2).The nourishment material of the beach is of terrigenous origin, those are Quaternary breccia and torrential proluvial material.As the beach is of southern exposure it is exposed to waves from the southern quadrant (Figs. 1 and 7).
Zahvaljujući podacima DHMZ-a meteorološke shore of the island (43° 10' N and 16° 27' E) in the town of Hvar and is only 15 km away from the research area.
According to its geographic position, as well as other Central Dalmatian islands, Hvar has a Mediterranean climate, according to Köpen's classification -the Olive Climate -Csa (Zaninovi et al., 2008) what is visible on the climatic diagram (Fig. 4).The specificity of the olive climate is a dry period in the warm part of the year, where the driest month has below 40 mm precipitation.Also, this climate type is characterized by hot and very clear summers, and mild, rainy and windy winters (Zaninovi et al., 2008).
According to the elongation of the island and its relief properties there are microclimate differences.The most prominent are the differences between the centre and the coast of the eastern and western parts of the island.The Island of Hvar is often called the "sunny Hvar" because it records the largest number of sunny hours in Croatia.
The long-term average (1952 -2015) of insolation is 2735.8h/year, while for example the annual extreme of 2003 reaches 3054.3 h/year (CMHS).According to CMHS data, the largest insolation is characteristic for July, whose long-term average
The annual temperature is influenced by insolation, geographical position, distance from the sea and the wind.From the climatic diagram, which shows the average air temperature (1867 -2015) for a period of 148 years, it can be seen that the mean air temperature in the coldest month of January is 8.7 °C, while the mean temperature of the hottest month, July, amounts to 25 °C.
The graph of air temperature (Fig. 5) reveals a trend of rising temperature for about 1 °C during the period of measurement.The increase in air temperature indicates warming, which results in different changes such as increasing rainfall extremes (Patari et al., 2014) and generally more frequent occurrences of different extreme events.
According to the climate of olive, the annual rainfall has a peak in November and December (about 102 mm) and a minimum in summer, in July (22.6 mm) when the air temperature is highest.According to CMHS data (1867 -2015), the average annual total rainfall at the Hvar station is 755 mm.
The amount of rainfall increases from the open sea to the land and depends on relief properties.There are also significant differences between precipitation amounts on the western and eastern part of the island.The western part is open towards the open sea, while the eastern part is under the influence of the mountain Biokovo, which affects the increase in rainfall from the west to the east.At the eastern end, the average total rainfall was, for example, in 1974, up to 1110 mm (Makjani, Volari, 1977).
On the study area sirocco, bora and mistral wind predominate.Bora occurs throughout the year, but is most prevalent in winter and mostly affects the northern side of the island.Winds from the southeast quadrant (mostly south) dominate at the opposing side of the island.Sirocco dominates in the cold part of the year.In the summer, a mistral appears which brings freshness and alleviates the summer heat.
Područje istraživanja spada u kategoriju mikro-of the island.Sirocco has a much smaller impact on the eastern part of the southern side, unlike the western part that is directly exposed to it.In the open sea the fetches are long and waves are bigger.The maximum measured wave height during sirocco wind in the Central Adriatic area was 8.4 m (Peljar za male brodove I dio, 2002).
According to the data from the Hvar meteorological station the wind rose was being constructed since the beginning of measurements (1867 -2015), showing that the most frequent and strongest winds comes from the Southeast quadrant (Fig. 6), while the north-eastern, north-western and western winds are slightly less expressed.The significant influence of the northern wind is also evident.It is a characteristic wind for the open sea and is more often and stronger in winter than in summer (Penzar et al., 2001).
According to the sea temperature data (CMHS) for the period 1964 to 2015, as shown in Figure 7, the sea temperature raised by 1.1 °C.
The study area is in the category of micro-tidal coasts with an average amplitude of ± 25 cm, Split tide gauge, (Čupi, personal communication), so tides do not have a major influence on coastal morphology (Raji et al., 2010;Faivre, Butorac, in press).

METHODS AND MATERIALS
In this paper, the method of repeat photography was used, also called the rephotography.It implies a repetition of photographing of a visual phenomenon or a physical location (Metcalfe, 2016).The principle of the method is to determine changes in an area based on a photography taken from the same location at different time intervals (Raji et al., 2010), and it is suitable for observations of an area during a longer period of time (Turner et al., 2003).Therefore, the method of repeat photography enabled this research.
First steps in developing the method of repeat photography were made by the Bavarian mathematician who dealt with glaciology (Webb et al., 2010) so the roots of repeat photography can be found in the Alps of central Europe.In 1888 Sebastian Finsterwalder began a photogrammetric study of mountain glaciers in Tyrol.The following year he came again to the same point and took a picture of the same view.By comparing new and old photographs with the help of rudimentary photogrammetry Finsterwalder documented glacier changes over time (Hattersly-Smith, 1966;Webb et al., 2010).Following the example of Finsterwalder, many geomorphologists of that time used repeat photography and influenced its development, for example, K. Gilbert (1904) in US and E. Cavell (1983) in Canada.Besides geomorphological studies, the method of repeat photography began to be used to document plant species and landscape changes (Clements, 1905).Since the 40s of the last century, repeat photography method has been increasingly used in documenting landscape changes, particularly related to changes in land use, while its use in geomorphology became more and more diverse.It is used, for example, in the analysis of weathering (Bryan, La Rue, 1927), estimation of backward erosion intensity (Longwell et al., 1932), analysis of activity of slope processes (Lobeck, 1939) etc.It has also recently been used in social sciences e.g. in sociology (Metcalfe, 2016).
The method of repeat photography was applied in different disciplines, but it has the greatest significance in geosciences (geography, geomorphology) and environmental sciences as repeat photography calfe, 2016.).
Tri osnovne metode primijenjene u ovome radu se kombiniraju i nadopunjuju.Rad se temelji na definiranju razlika u veličini žala između dviju generacija orto-foto snimaka (1968. i 2011. godine).Budući da na navedenim snimkama nije moguće točno odrediti obalnu granicu žala, ova se metoda kombinira (nadopunjuje) metodom ponovljene gives the ability to interpret a large number of parameters and allows an interdisciplinary approach.The method itself cannot provide the same type of quantitative data that can be obtained by satellite images and aero-photogrammetry, but it can be an excellent supplement or can be used in combination with them.It can provide very specific information, sometimes even data for a longer period of time than provided by air photography.This is an excellent method for documenting long-term changes from the earliest available landscape photographs and can serve as a reference framework for assessing future changes.The importance of repeat photography as a method has increased in the light of current discussions on global climate changes.S. T. Rajčić et al. ( 2010) first applied the method of repeat photography in the study of morphological changes of beaches for a period of about 50 years.In this paper, the method was used to determine the markers to estimate the size of the beach in the 60s of the last century.
Geomorphological changes of beaches are often studied with the help of classical field profiling at different time intervals, most often when observing seasonal changes in beach morphology (Kraus, 2005).Development of technology over the last 50 years has also enabled the development of many new methods in research of beaches, such as GPS profiling (Morton et al., 1993), the use of aerophotogrammetric and laser recording and scanning, or today the use of unmanned aerial vehicles (drones).One of the newest methods for tracking changes in morphology of beach and its surrounding is the SfM photogrammetry that started to be used in Croatia (e.g.Pikelj et al., 2014;Ruži et al., 2014;Pikelj et al., 2015;Tomini, 2017).Today, different methods are often combined and complemented.
This paper is based on three basic methods that are combined and supplemented.The work is based on defining the difference in the size of the beach between two generations of ortho-photos (1968 and 2011).Since on these photographs coastal margins cannot be accurately determined this method is combined with repeat photography method for the reconstruction of the beach boundary in the sixties of the 20th century as well as with the fieldwork to supplement the data of actual situation.fotografije za okvirnu rekonstrukciju granice žala šezdesetih godina prošloga stoljeća te terenskim radom za nadopunu podataka današnje situacije.
Since photographs are personal (private), three most significant photographs have been chosen on which the benchmarks are drown which represent key elements for the reconstruction of morphological changes of the beach (Fig. 8).Benchmarks are prominent relief forms that can be reliably recognized and used for reconstruction.When the number of photographs is large it is possible to make a clear distinction between tides, of course with a level of error.
The current situation was defined by field mapping which took place in May and July 2017 with the help of the handheld Garmin GPS receiver (error ± 3 m).The boundary of the beach was measured in the field and determined on 6 measurements that were further averaged.This boundary defined in the field was further displayed on the ortho-photo from 2011.During mapping in the field, tides were taken into account using data from Croatian Hydrographic Institute in Split, i.e. measurements were made during the mean sea level.
The surface of the beach was measured in several ways.With the help of a GPS device, the surface was measured in the field by contouring the beach.The measurement was performed three times and the mean value was calculated.The surface of the beach was also measured by digitizing the state ortho-photos from 1968 and 2011 in GIS.
Possible impacts of anthropogenic activities were considered by tracking changes in land use in the wider research area and recording newer construction works.Data on land use changes from the 19th century were obtained by georeferencing the maps of the Franciscan Cadastre from 1834 (Mappe catastali, 1834) and by georeferencing ortho-photos from 1968 and 2011 from the State Geodetic Administration of the Republic of Croatia.Maps
Žalo Zogon izgrađeno je od šljunka i valutica te and ortho-photos are digitized by overlay method to define trends of land use changes in the investigated area through the three mentioned periods.In this study, forest surfaces (primarily aleppo pine and also maquis, Trinajsti, 1977) and arable land was distinguished.Within the category of arable land, areas with vineyards (old and young), olive trees, pastures and small areas of poor fertility were taken into account.All analyses were made using the ArcGis 10.2 software.

RESULTS AND DISCUSSION
The Zogon beach is shaped in the Quaternary breccia (Fig. 2) and in proluvial material of 1023 m long gully whose source lies at the foot of the highest peak of the Island of Hvar Sv.Nikola (Figs. 1 and 9).The gully and its proluvial fan (i.e. the beach) represent a small geomorphological system.Systems in geomorpholgy are conceptual models that describe the transfer of sediments and energy and thus link relief forms in particular area and provide a framework for the interpretation of relief changes.The proluvial fan, i.e. the beach, beside this proluvial material, is also nourished with material from abrasion of breccia in which the fan is shaped.Although it is a small and simple geomorphological system in which well-known geomorphological processes take place, numerous geodynamic aspects are still little known.
The topography of the drainage basin is an important parameter for controlling the hydrological conditions associated with the gullying on particular area (Faivre et al., 2011).Slopes of 12 to 32° are extremely susceptible for gullying processes, while the higher inclines, which are predominantly present in the peak area, and are more conducive to rock slide and rock fall, that is to collapse processes (Fig. 3).This is directly confirmed by the scree cone at the foot of the Sv.Nikola peak (Fig. 1b.).South exposure and higher temperature amplitudes can increase weathering.Inclination is usually considered to be one of the most important parameter affecting production and transportation of torrential material (Ruži et al., 2011).However, it seems that the connection between the slope of the drainage basin and the size of the beach is je direktno izloženo jakim valovima osobito iz južnog kvadranta (Sl.5.).Budući da jugo puše dugo i ravnomjerno i izaziva najviše valove (Peljar za male brodove I dio, 2002.),pretpostavlja se da su ti valovi imali najveći utjecaj na današnji izgled žala, te da i dalje imaju najznačajniji utjecaj na njegovu morfodinamiku.Izloženost žala direktno je utjecala na abraziju kvartarnih breča.S obzirom na to da se žalo nalazi na iznimno izloženom dijelu obale u odnosu na navedene vjetrove i valove, važnu ulogu u njegovu formiranju i zadržavanju materijala ima poluotok i Rt Nedjelja.
The Zogon beach is made of gravel and pebbles and is directly exposed to strong waves especially from the southern quadrant (Fig. 5).Since Sirocco, with intense and even gusts, generates the highest waves (Peljar za male brodove I dio, 2002) in the studied area, it is assumed that these waves had the greatest impact on today's appearance of the beach, and that they still have the most significant influence on its morphodynamics.Exposure of the beach directly affected the abrasion of Quaternary breccia.Given that it is located on the extremely exposed part of the coast in relation to the aforementioned winds and waves, the peninsula and cape Nedjelja play an important role in its formation and retention of sediment.
According to the information obtained from the local population, particularly intense gullying occurred in September 1955, when during an extreme rainfall event a torrent flow was formed resulting in supply of significant amount of sediment to the beach.The CMHS records rainfall in Sv.Nedjelja, since 1950, consequently, a considerable amount of rainfall in the database during September 11, 1955, was found (94.6 L /m 2 ) which can be related to information provided by the local population.It is interesting that an intense episode of gullying in the Kvarner area was also recorded in September (Faivre et al., 2011).Namely, maximum rainfall intensity, in the period 1981-2007 in the area of Island of Krk, appeared in September, which seems to be an optimum period for episodes of strong gullying.Rainfall intensity in July and August is twice lower than in September, so the gullying processes are less frequent (Faivre et al., 2011).
The beach was formed by natural processes, but it was also two times partly filled: in the 70s of the 20th century, and in 2011 due to the construction works on the access road to the beach.The same year, due to the reduction of the beach surface and the impossibility of accessing the southwestern part of the beach during high tides and/or waves during Sirocco, a passage was made from its west and north-western side.The beach was further filled with this material.This newly formed anthropogenic surface was not taken into account when calculating the actual surface of the beach.
The largest part of the shallow gully and its surrounding area was under vineyards in the observed period.Since the slope of the area is > 32° (Fig. 3) terraces were constructed on some segments of the gully (mainly on lower ones) that allowed the cultivation of vines but also the protection of the soil from erosion.Since the gully bed passes through the middle of the vineyards a space of 2 m is left between the terraces, in order to allow the gully functioning (Fig. 1c).Nevertheless, the construction of terraces certainly contributed to the reduction of the beach nourishment.It is not known when they were built.But, if the parallel to the development of viticulture on the Vis island is withdrawn, where most of the vineyard terrace was in use in the second half of the 19th century, and when the area under the vineyards was the largest (Faivre et al., submitted), it is very likely that the terraces were constructed in Sveta Nedjelja at the same time.Due to the favourable conditions for cultivation of vine both in Vis and Island of Hvars and the appearance of vine disease in Italy and France, the possibility of wine export opened up, first to Italy, and subsequently to France and Hungary (Politeo, 1978).
Na temelju definiranih repera izmjerena je udaljenost između današnje granice žala i granice 60-ih godina prošlog stoljeća te je vidljivo da se granica u razmaku od oko šezdeset godina pomaknula za oko 6 m prema kopnu.Eventualnu promjenu kopnene granice žala nije bilo moguće dokumentirati zbog nedostatka repera i antropogenih intervencija na žalu.Također, digitalizacijom žala s orto-foto tunnel.Until then Sv.Nedjelja was isolated, as the place could have only be reached by hiking trails or from the sea.The construction of the road led to building of apartments and the increase of the tertiary sector, while at the same time a partial abandonment of other agricultural activities (except viticulture) occurred.At the same time, the gully bed ceased to be cleaned and is therefore today overgrown with vegetation.In 2010, a fire road was build that also crosses the drainage basin, so the gully bed was filled.Filling the gully bed in several places has also influenced the reduction of beach nourishment.
Comparison of land cover between the 1968 and 2011in the wider study area also reveals differences.As it is the case on most of the islands, the vegetation cover was considerably reduced in 1968, which is clearly visible in the ortho-photos (Fig. 9), whereas today the entire eastern Adriatic coast is characterised by vegetation regeneration (Ruži et al., 2011;Faivre et al., submitted).The narrow area around the beach itself does not show any obvious differences in the vegetation density between these two periods probably due to the influence of waves (Figs. 9 and 10).
Recent trend of vegetation regeneration relates to the neglecting of the area around vineyards.The increased vegetation density reduces weathering intensity and all destructive slope processes.During intensive precipitation, vegetation and soil slow down and reduce the concentration of rain drops and streams, thereby reducing linear erosion.Therefore, the amount of material that arrives to the beach decreases, so its natural nourishment is reduced.Similar trends were recorded in the Kvarner area (Ruži et al., 2011).
Figure 10 shows the size of the beach during the two periods.On 1968 ortho-photo, due to lower vegetation density the bed of the occasional flow can be observed.The selection of benchmarks shown in Figures 8 and 10a was done in the frame of the method of repeat photography.The benchmarks were used for the estimates of the approximate margin of the beach shape in the 1960s.This limit is shown on the ortho-photo from 1968 (Fig. 10a).The current beach boundary (measured in the field) is shown on the ortho-photo from 2011 (Figure 10b).The length of the Zogon beach to-187 snimke iz 1968.godine, a uzimajući u obzir granicu žala aproksimiranu na temelju repera, površina žala tada je iznosila približno 240 ± 10 m 2 .Uspoređujući površinu žala iz 60-ih godina 20.stoljeća te površinu žala danas vidljivo je da se površina smanjila za oko 120 m 2 .Dobiveni rezultati upućuju na značajnu promjenu veličine žala tijekom posljednjih šezdeset godina, to jest da je danas žalo gotovo dva puta manje.
On the basis of the defined benchmarks, the distance measured between today's beach limit and the boundary in the 60s of the last century revealed that the boundary during the past 60 years shifted by about 6 m towards the mainland.The possible change of the landward boundary of the beach could not be documented due to the lack of benchmarks and to anthropogenic interventions on the shore.Digitizing the beach surface from the ortho-photos of 1968, and taking into account the margin of the beach approximated by the benchmarks, the surface was thus reconstructed to 240 ± 10 m 2 .If compared to the actual beach size it is noticeable that the beach has decreased in size about 120m 2 .This reveals that the beach exhibited a distinct change in size during the last 60 years, that is, it is reduced almost by half today.
A. Bognar (1990) stated that on sandy-pebble beaches of the Island of Hvar abrasion is poorly expressed.However, the results of this paper show that Zogon beach in the observed period is dominated by erosion.The impact of erosion is clearly visible not only through the horizontal component of the narrowing of the beach body (Fig. 10) but also through the vertical component of sediment reduction as shown in Figures 8d and 8e.
According to E. Bird (1985), 70% of the world's beaches today are marked by erosion which can be directly associated with the global relative sea level rise that according to some researches, began at the end of the 18th century (Jevrejeva et al., 2008) or others, later, at the end of the 19th and early 20th centuries (Kemp et al., 2011;Gehrels, Woodworth, 2013).
The recent increase in relative sea level has been recorded in the wider area of the Island of Hvar using different methods, e.g. on the Island of Vis (Faivre et al, 2010, Faivre et al., 2013), in the wider Makarska area (Faivre, Butorac, in press) and Šibenik (Shaw, 2013;Shaw et al., 2016).Tide gauges in the Adriatic Sea also record global sea level rise (Tsimplis et al., 2012).Therefore, it can be assumed that raising sea level is likely to affect Zogon beach.The sea level rise also reduces the potential cm (Orli, Pasari, 2013.)što može izazvati velike promjene na žalima istočne obale Jadrana.
During the similar period, the sandy beach of the Milna Valley on Island of Vis is also threatened by the relative sea levels rise, leading to the decrease in the size of the beach of ≈10 ± 2 m in 35 years (1976 -2009-2011) (Faivre et al., submitted).Beach erosion was noted on a number of natural beaches in Croatia (unpublished data).According to the new analyses, due to global warming, the expected accelerated sea level rise by the end of the 21st century on the global scale can be 62 ± 14 cm (Orli, Pasari, 2013), which can cause major changes of the beaches along the eastern Adriatic coast.

CONCLUSION
Studying changes in the gully-beach system, the complexity of natural and anthropogenic factors which influence on a small simple geomorphological system have been observed.With the help of the method of repeat photography, ortho-photos and field work, it was found that in the period from the 1960s in the 20th century till today the beach surface reduced by about 50%.The method of repeat photography allowed the definition of benchmarks and a rough reconstruction of the size of the beach during the 60s of the last century without which this work could not be done.As the beach is an accumulational relief form by its definition, its current erosion testifies the reversal in the evolution of the beach, which is highly influenced by natural and by anthropogenic processes.
Anthropogenic processes are related to construction works and to the land use changes.A greater impact on the sediment and energy transfer in the system was caused by the construction of vineyard terraces that directly affect erosion reduction, soil retention on slopes, and thus reduce nourishment of the beach.This process probably started much earlier than the period of observation and certainly had a significant impact on Zogon beach.If the 19th century data are compared with actual data, it is apparent that today's cultivated areas with grape vines and olive trees occupy about 15% less surface area than in 1834, indicating the spatial 189 S druge strane klimatske promjene dovode do recentnog izdizanja relativne morske razine na širem području što direktno utječe na eroziju žala.Zajedno sa snažnim destruktivnim utjecajem olujnih valova uglavnom južnih smjerova i antropogeno induciranim procesima, navedeni procesi sinergijski utječu na negativnu bilancu sedimenta na žalu Zogon danas.
Significant impulses in the system occur occasionally, some of which act constructively and others destructively on the body of the beach.The beach was nourished with episodes of intense gullying as well as with filling during different construction works.Opposing and long-lasting effects on the beach body were caused by modifications of the torrent bed during the construction of roads or due to the changes in land use.The reduction of the agricultural activity, even if of a minor significance compared to other areas along the eastern Adriatic coast, results in partial natural reforestation during the observed period, which also likely effect on the reducing the beach nourishment.
On the other hand, climate changes lead to the recent relative sea level rise in the wider area which directly affects the erosion of the beach.Together with the strong destructive influence of storm waves mainly of southern directions and anthropogenically induced processes, they synergically have an effect on the negative balance of sediment on the Zogon beach today.
The expected significant sea level rise by the end of the 21st century could greatly affect further erosion of beaches along the eastern Adriatic coast, which are the framework of the tourist offer.The further sea level rise could also have an impact on the reduction of potential relief energy and could influence on further changes in the gully-beach system.

Figure 
Research area (a); larger area of the gully (b); terraces with vineyards and gully bed (c); Zogon beach (d & e).

Figure  .
Benchmarks used to reconstruct beach morphology in the 60s by means of repeat photography method (figures from: a) 1959, b) 1962, c) 1959) in comparison with actual situation (figures d), e), f ), g), h) from 2017).