Initial foredune field as a factor of accumulative character of coastal dunes of the Swina Gate...

O c e a n o l o g i c a l a n d H y d r o b i o l o g i c a l S t u d i e s I n t e r n a t i o n a l J o u r n a l o f O c e a n o g r a p h y a n d H y d r o b i o l o g y

Vol. XXXII, No.1

Institute of Oceanography ISSN 1730-413X

(39-58) 2003

University of Gdańsk eISSN 1897-3191

Copyright© by Institute of Oceanography, University of Gdańsk, Poland www.oandhs.org

Initial foredune field as a factor of accumulative character of coastal dunes of the Swina Gate Barrier (west Polish coast)

Tomasz Arkadiusz Łabuz1

Institute of Marine Sciences, Faculty of Natural Sciences ul. Felczaka 3a, 71-412 Szczecin, Poland

Key words: dune ridge, foredune formation, initial foredune field, accumulation, pioneer vegetation, wind directions

Abstract

Many of the Polish sandy coasts covered by several dune ridges are in danger, threatened by high wave storms and sea level rise. Some of the sandy coasts are accumulative. Accumulated on beach sand may cause growth and development of ridge. When upper beach at the front of the first dune is densely covered by plants sand may be fixed on beach. In this way on the upper beach may be built small hillocks or shadow dunes. It is important to know how fast a new dune ridge rises. This paper shows the importance of dune field formation on the upper beach in front of the foredune for new dunes accumulation. This field has possibilities to change in an initial dune ridge. Continuous aeolian accumulation of the sand on the dune field leads to the building of a new dune ridge. This process was observed on spit of Swina Gate Barrier on west Polish coast. The accumulation was forced by pioneer vegetation, which was covering hillocks and trapping transported sand from the beach. Also speeds and wind directions (measured in Świnoujście) may cause bigger and faster accumulation.

1 [email protected]; +48 91 444 15 92

Original research paper

T. A. Łabuz

Copyright© by Institute of Oceanography, University of Gdańsk, Poland

40

Author observed this process during five years on area of accumulative dune coast (the Swina Gate Barrier, west Polish coast). Before the beginning of the investigations, the upper beach in front of the foredune was covered by separated hillocks fixed by pioneer vegetation. After five years these hillocks became the new foredune ridge.

INTRODUCTION

Dune barriers belong to a very dynamic coastal ecosystem. They grow in accumulative conditions of the coast (Bird 1969; Hesp 1984, 1988; Psuty 1988, 1990, 1992; Shuiski 1986; Carter 1990a; Arens 1994; and others). The first dune ridge closest to the beach is foredune (Hesp 1981, 1984, 1988; Carter 1988; Carter, Wilson 1990c; Psuty 1990). The most important factors in dune development are aeolian processes caused by the wind and plants vegetation.

It is known, that Polish Baltic coast is threatened by high waves and strong storm surges (Wiśniewski 1975, Dziadziuszko and Jednorał 1988, Rotnicki and Borówka 1990, Zeidler et al. 1995). Majority of Polish coast is being eroded by sea and retiring on the south (Bohdziewicz 1963, Rosa 1963, Zawadzka-Kahlau 1999). Accumulation of the coast is observed only in a few places. One of them is The Swina Gate Barrier (Bohdziewicz 1963, Musielak 1991, Musielak 1995). This spit is localised on the Wolin and Uznam islands on the Pomeranian Bay coast (Fig. 1). In Polish borders spit has about 16 kilometres from morenic plateau in Międzyzdroje (Wolin Island) to country border in Świnoujście (Uznam Island). Both islands building spit are crossed by Swina river outlet, which is connected by Szczecin Lagoon and Pomeranian Bay.

Spit barrier became as a result of sea sand accumulation that comes from nearby abraded cliffs on Wolin and Uznam (Keilhack 1912, Rosa 1963, Piotrowski 1999, Osadczuk 2001). Part of spit on Wolin Island was built by material brought from Międzyzdroje, east direction where begins cliffs. Granulometric measurements of the sand from the seashore and sand from dune ridges on this part of spit prove this. Sand grains become smaller from east direction to west (Baraniecki and Racinowski 1989, Osadczuk 2001).

Today dune ridges coming from different accumulation stages cover all spit. They differ from each other by the morphology, lithology and ridges direction showing following phases of spit increase and development (Keilhack 1912, Rosa 1963, Borówka 1990, Piotrowski 1999, Osadczuk 2001). Also soil processes and plant succession is changing on older and younger ridges (Piotrowska, Celiński 1965, Prusinkiewicz and Noryśkiewicz 1966). Oldest Brown Dunes have heights to 5 m. They are dated from Atlantic Period, 5 000 years BP (Prusinkiewcz and Noryśkiewicz 1966). Following stages of spit development and growing of the yellow dunes led to cut off recent Szczecin Lagoon from Pomeranian Bay. In this time oldest brown dunes closest to the cliff were slowly abraded. From historic times (XV - XVII century) are dated

Initial foredune field as a factor of accumulative character

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Fig. 2. Location of the study area. A-wind rose for Świnoujście (own work out), B-map of study area (see fig. 2).

Fig. 2. Profiles localisation on study area.

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formation of the younger dunes called Yellow Dunes (Keilhack 1912, Rosa 1963, Borówka 1990, Piotrowski 1999, Osadczuk 2001, Osadczuk et al. 2001). The youngest dunes growing up since XVIII century (Keilhack 1912, Piotrowski 1999, Osadczuk et al. 2001). Man activity, which appeared at this time, led to cut of forests fixing older dunes. In this result aeolian processes caused formation of big transverse dunes which move over Yellow Dunes. (Rosa 1963, Osadczuk et al. 2001). Their heights reach 22 meters. In west part of Wolin spit they are divided in two ridges. They are called White I (Osadczuk et al. 2001). The youngest one closest to the coastline differs from transverse ridges. They look like coastal ridges. Their heights are not bigger than 7 meters. They are called White Dunes II (Osadczuk et al. 2001). In result of abrasion in eastern part spit, not far Międzyzdroje yellow dunes and high transverse ridges are closest to the sea. In west direction - to Świnoujście - number of the younger ridges and distances between them grow (Osadczuk et al. 2001).

Also recently increase of spit is being observed (Musielak and Osadczuk 1995). Analysis of coastline and beach width described on air photos (since 1951) proves progradation of the coast (Musielak et al. 1991, Musielak 1995). Near Swina outlet barrier proceeds 1.5 - 2 m per year (Musielak and Osadczuk 1995).

The effectivity of long period winds noted in Świnoujście (1961 – 1993) favours to transportation of material from beaches and accumulation dunes at the back of the beach (Borówka 1999).

In short period of time dynamics of this development did not yet become recognised. During investigations on beaches of Swina Gate Barrier in 1996 and 1997 author observed continued development of small aeolian forms on the upper beach. Seeing these investigations were undertaken which aim was to register changes in morphology of the foredune and upper beach. The main aim of the study was to show meaning of aeolian accumulation on foreground of foredunes for development of new ridges on accumulative spit coast of Swina Gate Barrier. Realisation of this work was possible thanks of registration of beach and foredune relief changes in chosen points in longer time.

MATERIALS AND METHODS

The studied site is located in the middle part of The Swina Gate Barrier on Wolin Island (Fig. 1, 2), between kilometre 419 and 423 of Polish coastline division (according to Polish Maritime Institute). Area of fieldwork was chosen basing on field reconnaissance executed in winter 1996.

The investigations were done on two first dune ridges (so-called White Dunes II according to Osadczuk 2001) and beach. They were divided into two


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stages. One of them were morphological measurements of aeolian relief. Second stage was qualifying of vegetation kind growing on beaches and foredunes.

During measurement were used geodesic tools, as leveller and theodolite. Also was used measure tape (30 m long) and carpenter's metre. Measurements depended on levelling of beach and dune ridges and checking distances among forms and width of beaches. Basing on literature of object, area of upper beach constantly covered by accumulative aeolian hillocks, shadow dunes, embryo dunes and by pioneer dune vegetation (Bird 1969; Hesp 1981, 1984; Carter 1990a, 1990b; and others) was called as a filed of initial foredune.

Kind of vegetation specimens were recognised basing on accessible books and lists of dune plants (Piotrowska and Celiński 1965, Łukaszewicz 1992, and others). Executed measurements points were marked on topographical maps of this region (1: 25 000, 1: 10 000) and on Fotointerpretation Atlas of Pomeranian Bay coastline made in scale 1:5 000 (Musielak et al. 1991).

Primary measurements were made in December 1997. In chosen points were made morphological profiles across youngest dunes through beach to waterline. Four profiles between 419-420 km, three between 420-422 km, and three between 422-424 km of the coastline (Fig. 2). Besides were made two comparative profiles near 417 km. Farther from that point in Międzyzdroje direction measurements were not been done because of vanishing of aeolian forms from the beach. These profiles were done in different season throughout the year. On every profile is written measure date and azimuth of cross-section. Azimuth of the each profile was the result of water line direction. Every profile was made in straight angle to coastline (Fig. 3). Start points (base points) of the profiles were chosen on older dunes fixed by herbaceous plants. Some of them were localised on second dune ridge and some at the back of these dunes before pine forest. The real height over ground of every base point is between 2 and 3 meters (counted from map). At present it is not possible to check real height of the start points as its difficult to investigate ground. But soon not only relative height will be known. Author will be using GPS station to check real height. On the height axis of the profile zero level was marked in base point to help with easy comparing of the changes in heights on dunes and beach. Height of one meter on the profile counted over base point was marked using dashed line. Height of –2 meter was marked as x-axis of the profiles. In such system it is easy to read changing levelling of the dunes and beach. Also zero point in the distance was marked there to compare changeable in time beach (Fig. 4).

The longest profile was made in middle part of study area (420.6 km) but then was shortened. Mean length of the profiles was 100 meters. It was caused by width of the youngest dunes. Zero point on profiles 423 and 423.4 is on the forest border line growing in lowering between forested white dunes II (so called by Osadczuk 2001) and not forested the youngest one. Zero point of

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0 40 80

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Fig. 4. Crossection profiles through Youngest Dunes & beaches of study area: 1 - new ridge from 2001, 2 - foredune ridge from 1997, 3 - date of profile made with psammophilus grasses cover (Ammophila arenaria, Ammophila baltica, Elymus arenarius), 4 – full cover by the grasses, 5 – less than half cover by the grasses.

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profile 420.6 is 72 meters in north direction form forest border line. Zero point of profile 419 is 50 meters in north direction from that forest. So is clearly visible, that area of youngest not forested dunes is the widest in middle part of field work and narrowest in west and east part. In west part the youngest dunes with beach have about 120 m with 3 ridges. In middle part from forest is about 170 m with 4 ridges and in east: 110 meters with 3 ridges. Of course this area is changing with water level in different season. On the figures was presented only part of the profiles. This part of profiles which shows relief of secondary dune, primary dune (foredune) and beach relief.

During investigations in 1997 also was recognised kind of vegetation and borders of plants on the beach. Also photos of the plants and relief were made. Dunes on the figures are not forested one. Only presence of pioneer grasses was marked on profiles. Dashed line for not full cover and continuous line for full grass cover.

Measurements were repeated in year 1998. From bad reason of marking profile points and of quick changes of beach-dune relief many of the repers were lost. Only in several places was possibility to recover firstly done measurements.

In the same points were made profiles on 423.4, 423, 422, 420.6 and 419 km of the Polish coastline kilometrage division. In that time few profiles were done in new place. Also measurement date was different for each other profile and caused by other observations date. Azimuth and length were the same. Also at this time was checked kind and changes in vegetation cover. In many not measured areas were done numerous sketches of dune and beach relief, and drawing examples of the plants causing accumulation.

Among year 1998 and 2001 measurements were not being done. During that period only observations, photos and some drawings of the plants and relief changes were done.

Renewed levelling measurements of dunes and beach relief in spring 2001 were caused by big changes in coastal dunes. During these measurements again were made profiles across dunes and beach. On each dune ridge a detailed account was made describing all plants specimen. For confirmations of changes were made numerous drawings and photos of the aeolian relief.

From year 2001 area of fieldwork was included into bigger study area on the spit (from 413 to 428 km). Latest results yet not worked were made in spring, summer and autumn 2002. It was observed, that new foredune still exist and are changing. But in some places was break by storm surges during winter 2001/02 year.


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RESULTS

Analysis of collected materials proves that coast of Swina Gate Barrier still has accumulative character. Through all investigated and observed period from 1996 to 2001 on upper beach become a new dune ridge. Firstly beach covered by sandy hillocks and shadow dunes change into new foredune. This zone was called filed of initial foredune. Mean width of the beach was about 60-70 meters.

At the beginning of the fieldwork upper beach up to 30 meters from foredune base was covered by numerous small aeolian forms. Their heights reached from 0.1 to 0.5 meters. In vegetative season this field was covered by pioneer grasses Ammophila arenaria, Ammophila baltica (Calammophila baltica) and Elymus arenarius. But denser growing plant was Honckenya peploides, halophilus plant of seaside beaches (Table 1). Aeolian forms on beach were separated from each other with deflation lowerings - blowouts. Their bottom was covered by organic material (shells, algaes, branches, grasses roots). First, closest to the beach dune ridge had abraded seaside slope. Its shape shows influence of sea waves in modelling of this dune ridge. Mentioned pioneer grasses covered this ridge. On its top were accumulated not large sandy tongues (up to 0.2 m). On the landward slope accumulation was small or absent because of existing mosses and lichens fixing the sand.

Table 1 Plants growing on the initial foredune field on Wolin part of Swina Gate Barrier.

Dune hillocks Blowouts Plants

Very dense dense rare Very dense dense rare

Ammophila arenaria Ammophila baltica Elymus arenarius Honckenya peploides

+ + + +

+

+

+

+

Festuca rubra arenariaCakile maritima Salsola kali

+ + +

+ + +

Petesities spurius Phragmities communis

+ +

+ +

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The widest field of initial foredune was localised in west part of study area. Very numerous pioneer plants covered this section. On neighbouring area in eastern direction these field became more and more small as a beach width. It was completely disappearing before Międzyzdroje town, where the beach had not exceed 35 meters. Also pioneer vegetation from the beaches in eastern direction was becoming rare and vanished near Międzyzdroje.

Since year 1997 described aeolian forms were becoming bigger and bigger. In some places they became connected with foredune slope. They looked like long tongues running crosswise to the ridge and water line and fixed by grasses. At that time also density of vegetation was increasing. Honckenya peploides not adapted to very intensive burring by the sand (Łukaszewicz 1992, Łabuz 2002) became retiring from growing hillocks. On its were growing pioneer grasses. Denser grasses stopped more and more of sand. Highest hillocks and grasses became a bigger obstacle for transported from the beach sand. Accumulation on foredune ridge clearly became smaller. Gradually entered on it plants that not tolerating big accumulation and moving sand. This ridge was slowly stabilised. Firstly abraded seaside slope of this dune in result of aeolian accumulation became transformed in softly shaped form. Between this ridge and growing new one appeared deflation lowering - blowouts.

Between 1998 and 2000 small hillocks and shadow dunes arisen up to 1 m and were grown every year. Connecting each other they were created embryo dunes fixed by pioneer grasses. In the end narrowing lowerings among these dunes were filled up by sand. Embryo dunes were connected in one dune ridge localised simultaneously to old foredune (Fig. 5). Landward slope of this ridge was step and seaward slope flat. This new dune has no straight going ridge. It was built as one ridge consisted from jointed tops of embryo dunes.

Ridges of the embryo dunes were transverse to new foredune ridge. Described ridge reaches up to 1 m in west and east part of studied area. In the middle study part (420 – 422 km) became higher, up to 2 meters from the bottom of the beach. Also distances among new and old ridge were different in each part of spit. Widest was in middle part and narrowest on edges. The bottom of this new lowering was covered by small aeolian hillocks (heights to 0.2 m) fixed by pioneer grasses. Among them were deflation gutters filled by organic material.

Morphology of these lowering was very similar to older lowerings morphology. Before new foredune accumulation process and plant succession started again. In 2001 author observed a new fixed by grasses small hillocks on the upper beach (up to 0.2 m).


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DISCUSSION

Decisive influence on development of sandy barriers have waves energy and constant delivery of sand (Bird 1969; Hesp 1988; Letherman 1988; Psuty 1988, 1990; and others). Accumulation and development of Swina Gate Barrier is going from Atlantic Period (Keilhack 1912, Rosa 1963, Piotrowski 1999). Spit shore has tendencies for sediment deposition (Baraniecki and Racinowski 1989, Racinowski and Seul 1996). On shallow shore is accumulated much of

Fig. 5. Foredune and upper beach relief changes during time, near 420 kilometre of study area (A - picture from 1997, Honcnekya peploides cover small hillocks on the beach; B - picture from 2001, psammophilus grasses fix new dune ridge on the beach).

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material originating from abraded neighbouring cliffs (Keilhack 1912, Rosa 1963, Baraniecki and Racinowski 1989, Musielak and Osadczuk 1995). Beaches there are wide - one from wider on Polish coast - may reach 100 m (Musielak et al. 1991, Musielak 1995). During autumn measurements in 1997 beach was 110 m wide. On narrow beaches with negative balance of material transportation and dune accumulation is impossible (Psuty 1992). Average sea level and waves in Świnoujście are lower from other open Baltic coast stations (Jednorał and Dziadziuszko 1987, Zeidler et al. 1995). Probability of strong storm surges is one of the lower from the Polish open Baltic coast (Wróblewski 1975, Zeidler et al. 1995). Strong surges became seldom (Wróblewski 1975, Jednorał and Dziadziuszko 1987). The biggest shore sedimentation is in the west part of spit on Wolin Island nearest Swina breakwaters, smaller is in the middle part and in east part near Międzyzdroje is vanishing (Baraniecki and Racinowski 1989). Also the number of dune ridges is becoming bigger from east to west (Osadczuk et al. 2001). Mean diameter of the sand on older ridges of the White Dunes II is becoming smaller from Międzyzdroje to Świnoujście direction from ∅1.89 to ∅2.42 (Osadczuk 2001). Also complex of bar system in shore and beaches are widest in west part of spit on Wolin (Musielak et al. 1991, Musielak 1995). So on studied areas belonging to Swina Gate Barrier in Poland (Wolin Island) are existing good conditions for coast development. These mentioned factors favour to dune ridges development in studied area.

Coastal dunes come into being in result of aeolian accumulation of material blown from constantly supplied beaches (Bird 1969; Borówka II 1979; Hesp 1984, 1988; Shuiski 1986; Psuty 1988; Carter 1990b). Process this can reach the best development thanks to favourable wind speed, directions and influence of pioneer dune vegetation (Mielczarski and Onoszko 1968, Bird 1969, Minkiavicius 1972, Shuiski 1986, Hesp 1987, Carter 1988, Psuty 1990, Hesp and Thom 1990, Arens 1994, Borówka II and Rotnicki 1999, and others). Main wind directions are causing transport of the sand from the lower beach or along the beach up on the back of it. Growing on beaches and foredunes grasses stops transported by the wind sand. Plants break the wind speed causing sand accumulation and building up dunes (Bird 1969, Hesp 1987, Carter 1990, Arens 1994, and others). Probability of material accumulation will be bigger during vegetation period. On Swina Gate Barrier most numerous are winds from west and south directions (for years 1961-1993): S, SW and W (Borówka 1999). Winds from the west are often all year (Table 2). During winds blowing from west was observed material transportation along beach from west part of investigated area (nearest breakwater of Swina River) to central area (own observations). Most strong winds blow from northern direction, northeast and east (Łabuz 1998) – Figure 6. They have big meaning for accumulation in west part of the spit (from breakwaters of Swina outlet to 422 km), where shoreline


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and foredune have course NW-SE. These winds are often in spring period (Łabuz 1998) – Table 2. In that time most of all material blown from beach can be stopped by increasing on spring vegetation. In central parts among 421 and 419 km shoreline and dune ridges are running in W-E direction. Probably dunes in this part of spit are supplied by material blown from beach during winds from north directions. Probability of wind appearance from northern section also is greatest in spring. So there also sand can be stopped on upper beach by increasing grasses. Besides frequent winds from west section (in spring and summer) transport material from beaches of west part of spit to the middle part (own observations). Just in middle part of fieldwork field of initial foredune is widest and embryo dunes are greatest. Further to the east coastline changing direction on SW-NE. Winds from NW directions should transport material from

Table 2

Percentage of wind directions in Świnoujście in different seasons (1961-1996).

Season NW W SW S SE E NE N Silence Sum Spring 8.69 17.17 11.94 10.13 6.70 10.85 18.96 11.67 3.89 100

Summer 7.33 24.67 18.49 12.85 6.64 7.13 10.29 8.42 4.18 100 Autumn 6.55 20.66 21.89 20.59 10.33 6.98 3.23 6.76 3.01 100 Winter 3.36 19.38 10.05 19.57 10.35 10.98 6.51 5.54 3.26 100

Fig. 6. Percentage of wind speeds (m s-1) from different directions in Świnoujście (1961-1996).

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beach up on dunes but they are very rare. So maybe this causes smaller aeolian forms on the beach. There, beginning from 419 km was observed vanishing of dune forms from upper beach. Also initial foredune field is becoming narrowest. Grasses are becoming rare. In eastern direction disappears hallophilus vegetation like Honckenya peploides, which begins aeolian accumulation on beaches of the spit (Łabuz 2002b). Seaside slopes of first dunes are there steeper and more often abraded by sea. Dune relief of this part of spit also can be shaped by winds from west section. Between year 1961 and 1993 winds from south most often appeared in autumn and in winter (Łabuz 1998). They can cause negative balance of material blown off the ridges at the back and deliver material on field of initial foredune. In that time (autumn and winter) only dead plants cover dune ridges. These winds can also deflated existing and not covered hillocks on the upper beach. In autumn and winter season during south winds sandy material can be blown from all dunes and upper beaches along all spit in sea direction.

Plants determine obstacles are stopping transported sand. Investigations results say that 50 to 70% of sediment is stopped by grasses Ammophila sp. (Carter 1990). On Swina Gate Barrier most of the plants growing on the upper beach are Ammophila and Elymus sp. (Piotrowska and Celiński 1965, Łabuz 2002b). Photointerpretation of beach vegetation in period 1951-1996 on study area beaches shows that there is still growing a lot of plants, which can fix transported from the beach sand (Łabuz 1998).

Material deposition on beach grown by pioneer dune grasses can be 5-times greater than on foredune (Carter and Wilson 1990). Around plants grow up new aeolian forms so-called embryo dunes or shadows dunes (Hesp 1981). On upper beach of study area such forms were observed all time. When these hillocks reached heights over 0.5 m they began to stop more and more material. So at the back on foredune accumulation was stopped. Lack of accumulation influenced on disappearance of pioneer grasses from Elymo-Ammophiletum associations. Plants from following succession stages Helichryso-Jasionetum associations occupied their place. At favourable conditions for aeolian accumulation (winds, material deliveries, lack of sea abrasion) aeolian forms from the beaches may be stabilised during 1-2 years; and may be transformed into new foredune ridge (Carter 1990). This process described in presented work was observed from year 1996 to 2001. In that time on investigated area was not storm surges being able to break accumulated and destroy young dune hillocks.

Other data says that accumulation of the spit on Wolin is the biggest in the west part near breakwater of Swina outlet (Baraniecki and Racinowski 1989, Musielak 1995, Osadczuk 2001). But the biggest rate of dunes development is in the middle part of spit because of winds and plants.


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On investigated area best conditions for aeolian accumulation and development of foredunes are in middle part among 422 and 420 km coastline kilometrage. In that place, Pomeranian Bay coastline lies furthest in the south direction and cuts in Wolin spit. The processes of coastline levelling through sea accumulation in narrow cut in the land bays are well known (Bird 1969, Leontiew et al. 1982). In this part of spit dunes are not so wide and high. But distances among following ridges are greatest. They arose very fast during land progradation so they could not be one of the highest and widest, but may be build far from the older one. Also a lot of pioneer dune grasses grow there. They cover a very wide foreground at the front of the first dunes (1/3 of beach width). In west part of study area ridges are wider but lowerings or blowouts between them are narrower. These dunes grow slower so they are bigger but closer too each other. In eastern part ridges are high, but narrow and steep. Probably they are more often sculptured by storm surges and built up during longer time. Also the number of youngest, not forested ridges is bigger in the middle area. From the middle to the borders of study area field of initial foredune is becoming narrower to 10-15 meters. In the east direction this field disappears about 414 km of coastline kilometrage. In west part near to breakwater, which is as a obstacle for transported in shore material, beaches are wide but seldom covered by aeolian forms. Probably sand is removed with very often west wind in east direction to the middle part of spit.

Human impact, especially tourism has a negative influence on the dunes development. Men activity causes changes in dune relief and vegetation cover (Carter 1980, Pye 1990, Piotrowska 1995, Olsauskas 1996, and others). On Wolin spit coastal tourism is localised in two centres: Międzyzdroje and Świnoujście. On investigation site on beaches and dunes tourists are still rare (Łabuz 2002a). Now without tourists on the beaches foredunes still may chance to natural development. But in future tourism impact may be a danger for dunes natural processes.

CONCLUSIONS

Made researches proved, that on spit area of Swina Gate localised in west part of Wolin Island (west Polish coast) are still developing a new dune ridges. Marine accumulation of the sandy material moving from the abraded cliffs on Wolin, wide beaches, wind conditions and dense vegetation cover led to aeolian accumulation and development of new dune ridges.

Prevalent winds directions (W, SW, S) and prevalent speeds (N, NE, NW) which are being measured in Świnoujście favour to this development especially in spring, summer and autumn season.

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Development of the coastline led to extending of the beaches. In these conditions grasses may cover a bigger part of beach and initial foredune filed may be widest. This field is localised on the upper beach at the front of the foredune. Dense pioneer grasses still cover the upper beach so accumulation at the front of the primary dune may develop.

Most quickly this process is becoming in middle part of spit on Wolin, where the coastline is cut in the land farthest in south direction.

During increasing plants stops more of the sand. Small sandy hillocks are changing in to bigger one. At the end they are uniting and building one new dune ridge. This process is continuing on the extending beach. Large number of pioneer grasses have greatest meaning for stopping and fixing of transported material on the upper beach. So the existed primary dunes get less of sand and they are smaller than other dunes of the Polish spits.

During 5 years since 1996 on the upper beach of Swina Gate barrier has been developing a new dune ridge. This ridge has similar width and height as the old one. Parameters of accumulated ridges and nearest relief is different in west middle and east part of studied area. Also width of initial foredune field differ in each part. Existed on upper beach initial foredune field is covered by halophilus plants and pioneer dune grasses. In future and in good conditions for aeolian accumulation this field may change in to new foredune. The field of initial foredune is a good indicator of accumulative character of the coast.

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Initial foredune field as a factor of accumulative character of coastal dunes of the Swina Gate...

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