water

Article -Foredune Budget Response to Fluctuation. Curonian , Lithuania

Darius Jarmalaviˇcius*, Donatas Pupienis, Gintautas Žilinskas, Rasa Janušaite˙ and Viktoras Karaliunas¯ Laboratory of Geoenvironmental Research, Nature Research Centre, Akademijos 2, LT-08412 Vilnius, Lithuania; [email protected] (D.P.); [email protected] (G.Ž.); [email protected] (R.J.); [email protected] (V.K.) * Correspondence: [email protected]

 Received: 14 January 2020; Accepted: 17 February 2020; Published: 20 February 2020 

Abstract: Beach-foredune sediment exchange maintains a coastal system’s stability. Sea level fluctuation is one of the most important factors that modifies the beach and foredune sediment budget. This study aims to assess beach and foredune budget changes depending on sea level fluctuations. On the basis of annual measurements of cross- profiles on the Curonian Spit in Lithuania, the sediment volumes on the beach and foredune and their changes between 2002 and 2019 were calculated. The sea level fluctuations were examined in parallel. The obtained data revealed that in the case of a sand surplus, a relatively low does not have a significant impact on the development of a foredune (and a minimal impact on a beach) on a decadal time-scale. Short-term sea level fluctuations are reflected in year-to-year variability in a beach sediment budget. However, no significant relationship between year-to-year variability in sea level fluctuation and the foredune sediment budget has yet been identified, nor is there a reliable year-to-year variability relationship between the foredune and beach sediment budget. The foredune sediment budget remained positive both through an increase and a reduction in the sediment volume on the beach.

Keywords: sea level; coastal ; coastal morphometry; Baltic Sea

1. Introduction The global mean sea level has been rising during the past century [1]. Based on satellite data, the rate of sea level rising has peaked at 3.36 mm/yr since 1993 [2]. The sea level trend in the Baltic Sea is similar to the global mean sea level trend [3]. Global climate change and sea level rise are often related to increasing and associated socio-economic transformations in coastal regions [4,5]. One of the most important problems in predicting future coastal evolution is determining the impact of a potential rise in sea level on coastal systems. However, there are other significant factors that also influence coastal dynamics including the geologic framework [6,7] and sand availability [8–13]. It is worth noting that coastal changes on short-term and decadal time scales are relevant to coastal managers and planners [14]. Within a decadal time period, there are other factors besides sea level fluctuation and geologic framework: extreme events [15–19], vegetation cover [20–23], human activity [24–26], and river discharge [27]. Since there is a complex interrelationship between sea level change and other factors on a short-term time scale, it is difficult to separate the direct impact of sea level on coastal systems from other factors. Depending on the interaction between various factors, accumulation processes may predominate on the despite the rising sea level [9,13,17,28,29]. Due to different driving forces, there can be high uncertainties related to the prediction of sea level rise impact on coastal systems [30]. The sand spits with predominant alongshore sediment transport are good examples for illustrating erosion and

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Water 2020, 12, x FOR PEER REVIEW 2 of 12 accretion processes along the shore [31–33]. Similar shoreline dynamic processes can be observed at illustrating erosion and accretion processes along the shore [31–33]. Similar shoreline dynamic the Curonian Spit where at the base of the spit erosion dominates, whereas on the distal end of the processes can be observed at the Curonian Spit where at the base of the spit erosion dominates, spitwhereas accretion on dominatesthe distal end [34 of,35 the]. Duespit accretion to the reduction dominates of sediment[34,35]. Due supply to the inreduction the southern of sediment part of the spitsupply and sea in level the southern rise, there part is intensificationof the spit and of sea erosion level rise [36, ].there Alongshore is intensification sediment of transport erosion [36]. directed northwardAlongshore creates sediment favorable transport conditions directed for northward accumulation creates near favorable the distal conditions part of the for spit.accumulation Thus, a huge sandnear mass the isdistal involved part of in the the spit. formation Thus, a of huge coastal sand mass is involved [37]. The in development the formation ofof foredunes coastal is closelylandforms linked [37]. to beach The development evolution and of foredunes the formation is closely of a linked beach-foredune to system and [38– the40]. formation Despite close interactionof a beach between-foredune beach system and [38 foredune,–40]. Despite these close two interaction components between of the beach system and do foredune not necessarily, these two evolve in onecomponents direction. of Forthe system example, do thenot necessarily foredune sand evolve budget in one may direction. be positive For example, while thethe beachforedune sand sand budget is inbudget equilibrium may be orpositive slightly while negative the beach [29 ,sand39,41 budget–43]. is in equilibrium or slightly negative [29,39,41– 43].Since 2002, annual changes in the beach and foredune sand volume have been monitored along the Since 2002, annual changes in the beach and foredune sand volume have been monitored along Lithuanian part of the Curonian Spit Baltic Sea coast. Between 2002 and 2019, the coastal dynamics in the Lithuanian part of the Curonian Spit Baltic Sea coast. Between 2002 and 2019, the coastal dynamics coastal systems with different geomorphologies were determined based on the obtained data. The aim in coastal systems with different geomorphologies were determined based on the obtained data. The of this paper is to evaluate the interrelationship between the beach and foredune sand budget, and aim of this paper is to evaluate the interrelationship between the beach and foredune sand budget, theand influence the influence of annual of annual mean mean sea level sea level fluctuation fluctuation on the on Balticthe Baltic Sea Sea coast coast in thein the Lithuanian Lithuanian part part of the Curonianof the Curonian Spit on aSpit decadal on a decadal time scale. time scale.

2. Study2. Study Area Area OfO thef the Lithuanian Lithuanian part part of of thethe CuronianCuronian Spit Spit (51 (51 km km long) long),, the the foredune foredune ridge ridge occupies occupies an area an of area of aboutabout 262.3 262.3 ha ha (Figure (Figure1 ).1). A A continuouscontinuous foredune foredune ridge ridge along along the theentire entire Curonian Curonian Spit was Spit formed was formed in in thethe second half half of of the the 19th 19th century. century. The The formation formation of the of foredune the foredune was started was started along the along shore the in shore in orderorder to to protect protect the the coastal coastal settlements settlements from fromsand being sand blow beingn and blown the andcoast thefrom coast wave from action. wave Semi action.- Semi-permeablepermeable sand sand fences fences were wereconstructed constructed along the along shore the between shore between 1810–1892 1810–1892 [41]. [41].

Figure 1. Location map. The black lines and numbers represent cross-shore profiles (Google Earth, earth.google.com/web/.).

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Figure 1. Location map. The black lines and numbers represent cross-shore profiles (Google Earth, Water 2020, 12, 583 3 of 12 earth.google.com/web/.).

When the ridge of accumulated sand reached 3 m in height it was planted with marram grass. Later on, the ridge developed without human intervention,intervention, except for being reinforced with tree branches in some places. Therefore Therefore,, human activity activity has has no crucial effect effect on foredune de development.velopment. The height of thethe foreduneforedune rangesranges fromfrom 66 mm atat JuodkrantJuodkrantėe˙ toto 1616 mm atat AlksnynAlksnynėe˙ (Figure(Figure2 ).2). StrikingStriking didifferencesfferences have alsoalso occurredoccurred inin thethe foreduneforedune volume.volume. The largest foredune is at SmiltynSmiltynėe˙ (up to 2200 m3/m)/m) and the smallest is atat JuodkrantJuodkrantėe˙ (110(110 mm33//m).m). The foredunes are densely covered with marram grass. The The widths widths of of the the beaches vary vary from from up up to to 65 65 m m at at Smiltynė Smiltyne˙ to to 30 30 m at Juodkrantė. Juodkrante.˙ The volume volume of of beach beach sediment sediment ranges ranges between between 124 m 1243/m at m the3/m Smiltyn at the e˙ Smiltynė and 42 m 3 and/m at 42 the m Juodkrant3/m at thee.˙ TheJuodkrantė. Curonian The Spit Curonian is formed Spit exclusively is formed ofexclusively Quaternary of deposits.Quaternary The deposits. upper part The ofupper the Quaternary part of the depositsQuaternary in thedeposits Curonian in the Spit Curonian is composed Spit is of composed of that sediments have been that formed have been in the formed basins ofin the variousbasins of stages the various of the Balticstages Sea’sof the development—starting Baltic Sea’s development from—starting the Baltic from Ice the Lake Baltic and Ic endinge Lakewith and recentending marine with recent sediments marine [34 sediments]. The beach [34]. of theThe Curonian beach of Spitthe Curonian is composed Spit of is finecomposed and medium of fine sand. and Meanmedium sand sand. grain Mean size sand ranged grain from size 0.2 ranged mm at from Smiltyn 0.2 e˙mm to 0.5 at Smiltynė mm at Juodkrant to 0.5 mme.˙ at Juodkrantė.

Figure 2. Typical cross-shore profiles and mean values of beach width and foredune height. Figure 2. Typical cross-shore profiles and mean values of beach width and foredune height. As the tidal range of the South-Eastern Baltic is not significant and barely reaches As the tidal range of the South-Eastern Baltic coasts is not significant and barely reaches 3.5–4.0 3.5–4.0 cm [44,45], the wind-generated waves [46], the prevailing alongshore currents, and accordingly cm [44,45], the wind-generated waves [46], the prevailing alongshore currents, and accordingly the the sand transport from south to north [35,47–49] and the aeolian processes [42] are the main sand transport from south to north [35,47–49] and the aeolian processes [42] are the main beach- beach-forming factors on the Lithuanian Baltic Sea coast. The most significant short-term sea level forming factors on the Lithuanian Baltic Sea coast. The most significant short-term sea level fluctuations near the Lithuanian coast occur due to storm surges. The most extreme storm surges are observed between November and February. In extreme cases, the sea level can rise up to 185 cm above Water 2020, 12, x FOR PEER REVIEW 4 of 12 fluctuations near the Lithuanian coast occur due to storm surges. The most extreme storm surges are observed between November and February. In extreme cases, the sea level can rise up to 185 cm Water 2020 12 above the, mean, 583 sea level [50] and wave height can reach up to between 4 and 6 m [46]. The 4most of 12 frequent recurrences of the storm wind directions are south-westerly (35.6%) and westerly winds (24.3%)the mean [51 sea]. level [50] and wave height can reach up to between 4 and 6 m [46]. The most frequent recurrences of the storm wind directions are south-westerly (35.6%) and westerly winds (24.3%) [51]. 3. Materials and Methods 3. Materials and Methods The sediment volume of the Curonian Spit beach and foredune (m3/m—cubic meters per meter of beachThe length) sediment was volumeassessed of based the Curonianon cross-shore Spit profiles. beach and The foredunecross-shore (m profile3/m—cubic was measured meters per at 29meter sites of in beach May length)of each was year assessed using Global based Navigation on cross-shore Satellite profiles. System The (GNSS cross-shore) Topcon profile HiPer was SR (Livermore,measured at CA, 29 sitesUSA) in with May a of horizontal each year accuracy using Global of ±1.0 Navigation cm and vertical Satellite accura Systemcy of (GNSS) ±1.5 cm. Topcon The levelingHiPer SR of (Livermore,all 29 cross-profiles CA, USA) was withdone ain horizontal calm weather accuracy over 16 of hours,1.0 cm therefore and vertical the morphometric accuracy of ± changes1.5 cm. are The insignificant. leveling of all Cross 29 cross-profiles-shore leveling was has done been in calm conducted weather at over fixed 16 hours, positions therefore from ± benchmarksthe morphometric installed changes some distance are insignificant. inland from Cross-shoreforedune to waterline. leveling has The been placement conducted of each at cross fixed- profilepositions has from been benchmarks chosen to correspond installed some with distance the best inland representation from foredune of the to general waterline. geomorphological The placement characteristicof each cross-profiles. Cross- hasshore been profiles chosen are to correspond denser where with there the bestis relatively representation high of variability the general in morphometricalgeomorphological characteristic characteristics.s. The Cross-shoresediment budget profiles (m3 are/m) denserwas established where there by comparing is relatively cross high- shorevariability profiles in morphometrical in two successive characteristics. years. Beach and The foredune sediment volumes budget were (m3/m) calculated was established separately. by Crosscomparing-shore cross-shore beach volume profiles is in defined two successive as the sand years. volume Beach and enclosed foredune by volumesbeach surface were calculated and the horizontalseparately. line Cross-shore from the beach waterline volume to the is defined foredune as thetoe. sandForedune volume volume enclosed is defined by beach as surfacethe volume and the of enclosedhorizontal sand line vertical from thely from waterline the foredune to the foredune toe to some toe. Foredunedistance inland volume where is defined the vertical as the variability volume of isenclosed negligible. sand The vertically cross-shore from p therofile foredune area was toe calculated to some distance using ArcMap inland where software. the vertical variability is negligible.Spacing The between cross-shore individual profile profiles area was is calculatedon average using 1.5 km. ArcMap The observation software. periods were from 2002 Spacingto 2019. betweenChanges individual in the sediment profiles volume is on average were calculated 1.5 km. The over observation time from periods the first were observation from 2002 into 2002. 2019. The Changes trend in of the beach sediment and foredune volume were volume calculated (m3/m overper year) time fromwas determined the first observation from the in linear 2002. regressionThe trend ofof beacheach andindividual foredune profile. volume A 95% (m3/ mconfidence per year) wasinterval determined was chosen from (p the-value linear < regression0.05). The heightof each of individual the foredune profile. in different A 95% confidence years was interval also determined. was chosen The (p-value sea level< 0.05). and Thefrequency height of of the the westerlyforedune wind in diff (SWerent-NW years direction) was also data determined. from the The Klaipėda sea level station and frequency between 2002of the and westerly 2019 windwere collected(SW-NW from direction) the Department data from theof Marine Klaipeda˙ Research station of between the Environmental 2002 and 2019 Protection were collected Agency. from Annual the meanDepartment values ofof Marinesea level Research and frequency of the Environmental of the westerly Protection wind were Agency. calculated Annual from mean daily values data. of This sea waylevel, seasonal and frequency variation of the was westerly eliminated. wind were calculated from daily data. This way, seasonal variation was eliminated. 4. Results 4. Results During the research period (2002–2019), the recorded sea level rise was 0.12 cm/yr (Figure 3). The obtainedDuring the trend research is not period statistically (2002–2019), significant the recorded(p > 0.05). sea A levelreason rise for was this 0.12 is the cm /largeyr (Figure interannual3). The variability.obtained trend However, is not statistically it was determined significant that (p >the0.05). sea Alevel reason has forbeen this rising is the at large a similar interannual rate (0.16 variability. ± 0.02 cm/However,yr) since it wasthe beginning determined of that the the20th sea century. level has been rising at a similar rate (0.16 0.02 cm/yr) since ± the beginning of the 20th century.

Figure 3. Sea level changes between 2002 and 2019 and their linear trends. Water 2020, 12, x FOR PEER REVIEW 5 of 12 Water 2020, 12, 583 5 of 12 Figure 3. Sea level changes between 2002 and 2019 and their linear trends. The marked sea level fluctuations in different years could have been the result of meteorological The marked sea level fluctuations in different years could have been the result of meteorological factors, in particular, cyclonic activity. This is proven by the frequency of westerly winds in 2002–2019, factors, in particular, cyclonic activity. This is proven by the frequency of westerly winds in 2002– as shown in Figure3. The relation between these characteristics (r = 0.77) is statistically significant 2019, as shown in Figure 3. The relation between these characteristics (r = 0.77) is statistically (p < 0.05). significant (p < 0.05). During the research period (2002–2019), no extreme storms occurred. The strongest storm, Ervin, During the research period (2002–2019), no extreme storms occurred. The strongest storm, Ervin, was recorded on 9 January 2005, when gusts of W-SW winds reached 28 m/s and the was recorded on 9 January 2005, when gusts of W-SW winds reached 28 m/s and the storm surge rose rose up to 153 cm [50]; on 5 December 2013 the storm surge resulting from southwesterly winds (up up to 153 cm [50]; on 5 December 2013 the storm surge resulting from southwesterly winds (up to 21 to 21 m/s) generated by storm Xaver reached up to 120 cm, and on 11 January, 2015 (storm Felix) m/s) generated by storm Xaver reached up to 120 cm, and on 11 January, 2015 (storm Felix) SW winds SW winds of 28 m/s elevated storm surge by up to 137 cm. However, due to a rapid beach recovery, of 28 m/s elevated storm surge by up to 137 cm. However, due to a rapid beach recovery, the erosion the erosion had no determinant influence on the long-term trend of the shoreline displacement and had no determinant influence on the long-term trend of the shoreline displacement and beach and beach and foredune sand volume variations. foredune sand volume variations. Despite sea level rise, a high alongshore variation of shoreline displacement was determined Despite sea level rise, a high alongshore variation of shoreline displacement was determined (Figure3). In the northern part, Klaip eda˙ port caused a seaward shoreline displacement up to (Figure 3). In the northern part, Klaipėda port jetties caused a seaward shoreline displacement up to 1.5 m per year, whereas in the central and southern parts the shoreline displacement rate ranges from 1.5 m per year, whereas in the central and southern parts the shoreline displacement rate ranges from 1.0 m/yr to 2.0 m/yr (Figure4). It was noticed that shoreline fluctuations vary over a wide range in −−1.0 m/yr to 2.0 m/yr (Figure 4). It was noticed that shoreline fluctuations vary over a wide range in individual years. Annual changes in individual cases may reach 20 m or more. This is also reflected in individual years. Annual changes in individual cases may reach 20 m or more. This is also reflected the p-value (red line in Figure4). Of 29 cases, nine trends are reliable ( p < 0.05). This indicates that in the p-value (red line in Figure 4). Of 29 cases, nine trends are reliable (p < 0.05). This indicates that changes in shoreline position did not have a clear trend. changes in shoreline position did not have a clear trend.

Figure 4. Linear trends (m/yr) in the shoreline position between 2002 and 2019. Red line—significance Figurelevel (p 4.-value). Linear Greentrends labels(m/yr) indicate in the shoreline cross-shore position profile between numbers. 2002 and 2019. Red line—significance level (p-value). Green labels indicate cross-shore profile numbers. Similarly, high variations of beach volume were determined in different coastal sectors (Figure5A). In theSimilarly, northern high part, variations the amount of beach of beach volume sand were has determined tended to increasein different (on coastal average sectors by 1–5 (Figure m3/m 5perA). year),In the whereasnorthern in part, the the southern amount part of itbeach has beensand decreasinghas tended (Figureto increase5A). (on It should average be by pointed 1–5 m out3/m perthat year), these whereas changes in beachthe southern sand volume part it inhas di beenfferent decreasing coastal sectors (Figure are 5A asynchronous.). It should be Forpointed example, out thatuntil these 2007, changes sand accretion in beach hadsandbeen volume the in dominant different trendcoastal in sectors the southern are asynchronous. part of the For investigated example, untilsector. 2007, In 2008,sand thisaccretion trend had changed been the to erosion. dominant Meanwhile, trend in the in sout thehern northern part of part the of investigated the Curonian sector. Spit, Inthis 2008, pattern this wastrend not changed observed. to erosion. In general, Meanwhile, permanent in sand the northern accretion part on the of beachthe Curonian in 2002–2019 Spit, onlythis patterntook place was in not the observed. northern partIn general, of the spitpermanent (the Smiltyn sande–Alksnyn˙ accretion one˙ coastal the beach sector), in 2002 predetermined–2019 only took by a placeblockage in the of thenorther alongshoren part sedimentof the spit transport (the Smiltynė by the– KlaipAlksnynėeda˙ port coastal jetties sector), [35,49]. predetermined In the southern by part a blockage(Pervalka–Nida), of the alongshore the variations sediment in beach transport sand volume by the followedKlaipėda no port definite jetties pattern. [35,49]. In the southern part (PervalkaDuring the–Nida), investigation the variations period, in the beach volume sand of volume foredune followed sand increased no definite along pattern. the entire spit coast except for short stretches near Pervalka and Preila (Figure5B). The foredune sand volume increased from 0.3 m3/m per year in the southern part to 3.9 m3/m/yr in the northern part. It should be noted that in the long term, no considerable variations in foredune sand volume were observed. Similar to the beach sand volume budget, the foredune sand volume variations in different coastal sectors were also asynchronous. Until 2007, sand volume variations in the northern part had been negligible,

Water 2020, 12, 583 6 of 12 whereas after 2007 the accretion rates have been increasing. In the southern part, this pattern has not Waterbeen 20 observed.20, 12, x FOR PEER REVIEW 6 of 12

Figure 5. Linear trends (m3/m per year) in the (A) beach and (B) foredune volume alongshore. Distance Figurefrom Klaip 5. Lineareda˙ port trends jetties. (m3 Red/m per line—significance year) in the (A) level beach (p-value). and (B) Green foredune labels volume indicate alongshore. cross-shore Distanceprofile numbers. from Klaipėda port jetties. Red line—significance level (p-value). Green labels indicate cross- shore profile numbers. It is worth noting that the foredune in the Lithuanian part of the Curonian Spit has grown since the endDuring of the the 19th investigation century [52 period,]. Between the 1859volume and of 1910 foredune (from thesand beginning increased of along foredune the entire formation) spit coastits height except increased for short from stre 2.3tches m (Juodkrant near Pervalkae)˙ to 8.9and m Preila (Smiltyn (Figuree)˙ (Figure 5B). 6 The). During foredune the sandinvestigation volume increasedperiod (2002–2019) from 0.3 m the3/m rate per ofyear foredune in the southern growth slowed part to but3.9 m remained3/m/yr in positive. the northern Averaged part. It foredune should beheight noted increases that in the at a long rate term, of 1.4 no cm /considerableyr. It was observed variations that in despite foredune the highsand variabilityvolume were of beach observed. sand Similarvolume, to almost the beach all (26 sand of 27 volume cases (Figurebudget,5B)) the trends foredune are statisticallysand volume significant variations ( p in< 0.05).different The coastal reason sectorsfor the slowingwere also down asynchronous. of foredune Unt growthil 2007, is the sand high volume elevation variations reached inin the the middle northern of the part 20th had century. been negligible,Due to high wher elevationeas after and 2007 dense the coverage accretion with rates marram have been grass increasing. on the western In the slope, southern sand part, particles this patternhardly reachhas not the been top ofobserved. the foredune. Therefore, the most accretion takes place at the foredune toe and westernIt is slope.worth Often,noting especially that the foredune in the northern in the Lithuanian part, incipient part of the are Curonian formed. Spit In recreational has grown zones,since thedue end to highof the pedestrian 19th century pressure, [52]. Between foredunes 1859 are and reinforced 1910 (from with the tree begin branches,ning of foredune which is formation) the second itsreason height for increased accretion from at the 2.3 foredune m (Juodkrantė) toe and westernto 8.9 m slope.(Smiltynė) The height(Figure of 6). the During foredune the hasinvestigation increased periodmore in (2002 the southern–2019) th parte rate where of foredune the foredune growth is lower,slowed while but remain in the northerned positive. part Averaged where the foredune foredune heightheight increases reaches up at toa rate 16 m, of the1.4 heightcm/yr. ofIt thewas foredune observed has that remained despite the practically high variability unchanged of beach for the sand last volume,20 years. almost Thus, all the (26 foredune of 27 cases grew (Figure rapidly 5B)) upwards trends are in statistical the earlyly 20th significant century, (pand < 0.05). currently, The reason with forsimilar the slowing accumulation down rates,of foredune it has been growth widening. is the Ithigh should elevation also be reached noted that in the between middle 2002 of andthe 20th 2019 century.there was Due not to an high appreciable elevation shoreline and dense and cover foreduneage with migration. marram grass on the western slope, sand particles hardly reach the top of the foredune. Therefore, the most accretion takes place at the foredune toe and western slope. Often, especially in the northern part, incipient dunes are formed. In recreational zones, due to high pedestrian pressure, foredunes are reinforced with tree branches, which is the second reason for accretion at the foredune toe and western slope. The height of the foredune has increased more in the southern part where the foredune is lower, while in the northern part where the foredune height reaches up to 16 m, the height of the foredune has remained practically unchanged for the last 20 years. Thus, the foredune grew rapidly upwards in the early

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20th century, and currently, with similar accumulation rates, it has been widening. It should also be Water20th 2020century,, 12, 583 and currently, with similar accumulation rates, it has been widening. It should also7 of be 12 noted that between 2002 and 2019 there was not an appreciable shoreline and foredune migration. noted that between 2002 and 2019 there was not an appreciable shoreline and foredune migration.

FigureFigure 6.6. ChangesChanges inin foreduneforedune elevationelevation sincesince 1859.1859. DistanceDistance fromfrom KlaipKlaipėdaeda˙ portport jetties.jetties. Figure 6. Changes in foredune elevation since 1859. Distance from Klaipėda port jetties. 5. Discussion 5. Discussion 5. Discussion It can be seen in Figure4 that over the last 17 years both the beach and foredune accretion processes It can be seen in Figure 4 that over the last 17 years both the beach and foredune accretion haveIt prevailed can be seen despite in aFigure rise in 4 sea that level over of theup to last 0.12 17cm years/yr. The both alongshore the beach sediment and foredune transport accretion from processes have prevailed despite a rise in sea level of up to 0.12 cm/yr. The alongshore sediment theprocesses southern have part prevailed of the Curonian despite Spita rise (Kaliningrad in sea leveldistrict) of up to is 0.12 the maincm/yr cause. The ofalongshore this sand accretion.sediment transport from the southern part of the Curonian Spit (Kaliningrad district) is the main cause of this Duetransport to the from sand the transport southern being part blocked of the Curonian by the Klaip Spiteda˙ (Kaliningrad port jetties, district the most) is intensethe main accretion cause of takes this sand accretion. Due to the sand transport being blocked by the Klaipėda port jetties, the most intense placesand accretion. in the northern Due to partthe sand of the transport spit [35 ,being49]. The blocked observed by the rate Klaipėda of sea p levelort jetties, rise does the most not stop intense the accretion takes place in the northern part of the spit [35,49]. The observed rate of sea level rise does dominantaccretion takes trend place of sand in accumulationthe northern andpart coastalof the spit accretion [35,49 [].43 The]. Even observed during rate storms, of sea the level sand rise washed does not stop the dominant trend of sand accumulation and coastal accretion [43]. Even during storms, the awaynot stop from the the dominant coast is trend returned of sand during accumulation the recovery and phase coastal and accretion is not reflected [43]. Even in the during long-term storms, sand the sand washed away from the coast is returned during the recovery phase and is not reflected in the budgetsand washed [41,53 ].away from the coast is returned during the recovery phase and is not reflected in the long-term sand budget [41,53]. long-Theterm influence sand budget of the [4 sea1,53 level]. rise taking place during decadal time span on coastal sand volume The influence of the sea level rise taking place during decadal time span on coastal sand volume changesThe isinfluence inconspicuous. of the sea Due level to rise erosion taking at place the Curonianduring decadal Spit base time (Kaliningrad span on coastal district, sand volume Russia) changes is inconspicuous. Due to erosion at the Curonian Spit base (Kaliningrad district, Russia) wherechanges coastal is inconspicuous. regression occurred Due to already erosion in at the the 19th Curonian century Spit [52] base large (Kaliningrad amounts of sand district, transported Russia) where coastal regression occurred already in the 19th century [52] large amounts of sand transported northwardwhere coastal helped regression to maintain occurred a stable already shoreline in the position19th century in the [52] central large part amounts of the of spit sand (between transported Nida northward helped to maintain a stable shoreline position in the central part of the spit (between Nida andnorthward Juodkrant helpede),˙ while to maintain in the northerna stable shoreline part (Alksnyn positione–Smiltyn˙ in the centrale)˙ shoreline part of displacementthe spit (between seaward Nida and Juodkrantė), while in the northern part (Alksnynė–Smiltynė) shoreline displacement seaward tookand Juodkrantė), place [52]. The while same in the process northern takes part place (Alksnynė in the early–Smiltynė) 21st century. shoreline A comparison displacement has seaward shown took place [52]. The same process takes place in the early 21st century. A comparison has shown that thattook theplace shoreline [52]. The displacement same process coincides takes place with in sandthe early volume 21st variationscentury. A oncomparison the beach has (Figure shown7) (the that the shoreline displacement coincides with sand volume variations on the beach (Figure 7) (the correlationthe shoreline is significant displacement at p < coincides0.05). Short with erosion sand periods volume do variations not reverse on the the general beach (Figureaccretion 7) trend (the correlation is significant at p < 0.05). Short erosion periods do not reverse the general accretion trend overcorrelation a long-term is significant period. at p < 0.05). Short erosion periods do not reverse the general accretion trend over a long-term period. over a long-term period.

Figure 7. Correlation between mean changes in the shoreline position and beach sand volume.

Water 2020, 12, x FOR PEER REVIEW 8 of 12 Water 2020, 12, 583 8 of 12 Figure 7. Correlation between mean changes in the shoreline position and beach sand volume. An analysis of the interdependence of changes in shoreline position and foredune sand volume An analysis of the interdependence of changes in shoreline position and foredune sand volume variations has shown no significant correlation (p > 0.05) (Figure8). Even during years with variations has shown no significant correlation (p > 0.05) (Figure 8). Even during years with predominated storm activity, the foredune sand budget has remained positive. The dominant sand predominated storm activity, the foredune sand budget has remained positive. The dominant sand accretion in the foredune takes place despite sea level oscillations or the beach sand budget. accretion in the foredune takes place despite sea level oscillations or the beach sand budget.

Figure 8. Correlation between changes in the shoreline position and foredune sand volume. Figure 8. Correlation between changes in the shoreline position and foredune sand volume. Despite a certain link between the beach and foredune sand budgets [39–41,54,55], as shown in FigureDespite9, no significant a certain link correlations between the between beach theand changes foredune in sand the beach budgets and [3 foredune9–41,54,55 sand], as shown budgets in haveFigure been 9, no determined. significantYet, correlations the weak between correlation the between changes the in beachthe beach and foreduneand foredune sand sand budgets budgets does nothave imply been andetermined. absence of Yet, interdependence. the weak correlation The interdependence between the beach is presumably and foredune complicated sand budgets by a does few circumstances.not imply an absence One is of the interdependence. morphological properties The interdependence of the beach [is56 presum]. Duringably storms, complicated narrow by beaches a few cancircumstances. be replenished One byis the foredune morphological sand, in properties this way retaining of the beach their [56 shape,]. During whereas storms, wider narrow beaches beaches can protectcan be replenished the foredunes by atforedune the expense sand, of in their this sandway budget.retaining In their the firstshape, case, whereas when thewider foredune beaches sand can budgetprotect isthe negative, foredunes the at beach the exp sandense volume of their will sand change budget. insignificantly. In the first case, In the when second the case,foredune the beach sand sandbudget budget is negative, will be the negative, beach sand whereas volume in thewill foredune change insignificantly. it will remain In unchanged the second or case, even the become beach positivesand budget [57]. Itwill is alsobe negative, important whereas that the beachin the andforedune foredune it will budget remain are notunchanged synchronized or even in time become [58]. Sandpositive accretion [57]. It on is aalso beach important takes place that during the beach calm and meteorological foredune budget conditions are not when synchroni a sandbarzed welds in time to the[58]. beach. Sand Meanwhile,accretion on foredune a beach accretiontakes place occurs during during calm a meteorological storm season [58 conditions,59]. This processwhen a maysandbar also bewelds influenced to the beach. by interrelations Meanwhile, with foredune adjacent accretion coastal o sectorsccurs during due to a alongshore storm season sediment [58,59]. transport This process [60]. Themay obtained also be influenced results showed by interrelations that if there is with a suffi adjacentcient amount coastal of sectors sand, even due a to slow alongshore sea level risesediment has a positivetransport eff [ect60]. on The the obtained foredune results sand budget. showed This that is if related there is not a onlysufficient to the amount alongshore of sand, transport even of a hugeslow amountssea level of rise sediments has a positive from the effect southern on thepart foredune of the spit sand [35,47 budget.–49], but This also isto smallrelated nearshore not only inclines, to the whichalongshore create transport favorable of conditions huge amounts for sandbar of sediments welding from to the the beach southern during part fair of weather the spit conditions[35,47–49],[ but61]. Inalso these to small circumstances, nearshore inclines, foredunes which that create are built favorable up at distal conditions ends offor some sandbar spits welding can build to the upwards beach despiteduring fair a sea weather level rise conditions [62]. Accretion [61]. In these was dominantcircumstances, in foredunes, foredunes even that in are coastal built up sectors at distal where ends a lowof some trend spits for can sand build decrease upwards was despite observed a sea on thelevel beach. rise [62 Such]. Accretion a situation was is dominant observed in at foredunes 16, 27, 35,, andeven 48 in km coastal from Klaip sectorseda˙ where port jetties a low (Figure trend5 ).for This sand has decrease also been was supported observed by investigationson the beach. carriedSuch a outsituation on other is observed coasts [29 at,39 16,,56 27,,60 35,]. and 48 km from Klaipėda port jetties (Figure 5). This has also been supported by investigations carried out on other coasts [29,39,56,60].

Water 2020, 12, 583 9 of 12 Water 2020, 12, x FOR PEER REVIEW 9 of 12

Figure 9. Correlation between changes in the beach and foredune sand volume. Figure 9. Correlation between changes in the beach and foredune sand volume. It is worth noting that prevailing accretion in the Lithuanian part of the Curonian Spit has taken placeIt since is worth the end noting of the that 19th prevailing century accretion [52]. During in the the Lithuanian 20th century, part of there the wasCuronian not an Spit appreciable has taken shorelineplace since or foredunethe end of migration. the 19th century Due to alongshore[52]. During sediment the 20th transport century, directed there was northward, not an appreciable rising sea levelshoreline may increaseor foredune coastal migration erosion. in Due the southernto alongshore part ofsediment the spit (Kaliningradtransport directed district) northward and the amount, rising ofsea sand level transported, may increase which coastal may erosion enhance in sediment the southern accumulation part of the in spit the northern(Kaliningrad part district) of the spit) and and the herewithamount of raise sand the transported, transported which sand amount, may enhance which sediment may lead accumulation to the accumulation in the northern of sediments part inof thethe northernspit) and part herewith of the spit. raise the transported sand amount, which may lead to the accumulation of sedimentsIt is assumed in the northern that coastal part erosion of the processesspit. start only when the sea level rise reaches a threshold valueIt higher is assumed than thethat present coastal rateerosion on theprocesses Lithuanian start only coast when of the the Baltic sea level Sea. rise According reaches toa threshold Pye and Blottvalue [63 higher], the ethanffects the of thesepresent changes rate on might the Lithuanian not be significant coast of for the at Baltic least 30–50Sea. According years. However, to Pye itand is worthBlott [ noting63], the that effects it is of impossible these changes to strictly might predict not be threshold significant value for determiningat least 30–50 erosional years. However, processes it to is beworth started noting because that theit is aforementioned impossible to strictly changes predict happen threshold very slowly, value so determining the coastal system erosional can process adapt toes theseto be alterations. started because It is also the unclearaforementioned what variations changes may happen happen very to theslowly, sand so supply, the coastal etc. system can adapt to these alterations. It is also unclear what variations may happen to the sand supply, etc. 6. Conclusions 6. Conclusions The present research showed that due to alongshore sand transport, the analyzed coastal sector is distinguishedThe present by aresearch sand surplus. showed Therefore, that due to a slowalongshore sea level sand rise transport, (up to 0.12 the cm analyzed/yr) has coastal no negative sector eisff ectdistinguished on the foredune by a sand and surplus. only a minimalTherefore, eff aect slow on sea beach level development rise (up to 0.12 on cm/yr) a decadal has no time negative scale. Noeffect significant on the foredune correlation and was only determined a minimal effect between on beach the changes development in foredune on a decadal sand budget time scale. and sea No levelsignificant fluctuations. correlation Also, was no significantdetermined correlation between the between changes the in changes foredune in sand foredune budget and and beach sea sand level budgetsfluctuations. was determined. Also, no significant Despite the correlation rise in sea level between and changes the changes in beach in sandforedune volume, and the beach foredune sand sandbudgets budget was remained determined. positive Despite almost the in risethe whole in sea area level of investigation.and changes inHowever, beach sand the absence volume, of anthe interrelationforedune sand between budget the remained beach and positive foredune almost budgets in the does whole not mean area anof absenceinvestigation. of interdependence. However, the Theabsence interrelation of an interrelation may have beenbetween complicated the beach by and a fewforedune circumstances: budgets does a time not lag mean in di anfferent absence links of (theinterdependence. beach in close The contact interrelation with the seamay tends have tobeen more complicated readily adjust by a tofew changing circums seatances: levels, a time whereas lag in indifferent the foredune links (the these beach processes in close lag contact behind). with Moreover, the sea tends the to foredune more readily sand washedadjust to away changing during sea morelevels, powerful whereas storms in the mayforedune compensate these processes for beach lag sand behind). losses, thusMoreover, preserving the foredune the unchanged sand washed beach sandaway budget. during more powerful storms may compensate for beach sand losses, thus preserving the unchanged beach sand budget. Author Contributions: Conceptualization, D.J.; methodology, D.J. and D.P.; formal analysis, D.J., D.P., and G.Ž.;Author investigation, Contributions: D.J., Conceptualization D.P., and G.Ž.; data, D.J curation,.; methodology, D.P. and D.J. R.J.; and writing—original D.P.; formal analysis, draft D.J., preparation, D.P., and G.Ž. D.J.;; writing—reviewinvestigation, D.J., and D.P. editing,, and D.P. G.Ž and.; data G.Ž.; curation, visualization, D.P. R.J.and and R.J. V.K.; writing All authors—original have draft read preparation, and agree to D.J the.; publishedwriting— versionreview and of the editing, manuscript. D.P. and G.Ž.; visualization, R.J. and V.K. All authors have read and agree to the Funding:publishedThis version research of the received manuscript. no external funding.

Funding: This research received no external funding.

Water 2020, 12, 583 10 of 12

Acknowledgments: The authors wish to thank Laurynas Jukna (Vilnius University, Lithuania) for technical support. Conflicts of Interest: The authors declare no conflicts of interest.

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