VULNERABILITY OF POLAND S COAST TO SEA-LEVEL RISE

Transcription

1 Coastal Engineering Journal, Vol. 47, Nos. 2 & 3 (2005) c World Scientific Publishing Company and Japan Society of Civil Engineers VULNERABILITY OF POLAND S COAST TO SEA-LEVEL RISE ZBIGNIEW PRUSZAK Institute of Hydro-Engineering, Polish Academy of Sciences, Gdańsk, Kościerska 7, Poland zbig@ibwpan.gda.pl ELŻBIETA ZAWADZKA University of Gdańsk, Department of Geomorphology and Quaternary Geology, Gdańsk , Dmowskiego 16a, Maritime Institute, Department of Maritime Hydrotechnics Gdańsk, Abrahama 1, Poland geoez@univ.gda.pl ela@im.gda.pl Received 10 June 2004 Revised 16 May 2005 Over the last decades, the Polish coast, about 500 km long and predominantly featured by sandy, low-lying beaches, has been exposed to various threats resulting from intensified climate change and Accelerated Sea-Level Rise (ASLR). This has manifested itself in the growing intensity of shoreline, dune and cliff erosion and by the increasing necessity of their protection. The current study is both a summary and an extension of the existing Polish studies and analyses on the present and predicted influence of ASLR on the coast. First, the Polish coast was divided into three basic area types (AREA I, II, III) according to their geographic and socio-economic background. Then, two different scenarios of accelerated sea-level rise (ASLR1 30 cm/100 yrs and ASLR2 100 cm/100 yrs) were assumed. After that threats of land loss and the risk of its temporary or partial inundation was analyzed in connection with the assessment of the material and social costs and losses. These analyses were made within the framework of two adaptation scenarios, i.e. retreat (do nothing) and full protection. The performed analyses have shown that the greatest threat of partial or full land loss and the associated material and social costs are expected to occur in two regions of the Polish coast. One of them is situated in the eastern sector of the Polish coast and covers the agglomeration of Gdańsk and the Żu lawy polders. The other is located in the west and comprises low-lying areas around the Szczecin Lagoon and the vicinity of the Odra river mouth. These areas both require intensive care and protection efforts. 131

2 Vistula River 132 Z. Pruszak & E. Zawadzka Keywords: Baltic Sea; coastline evolution and protection; sea-level rise; flooding threat of the Polish coast; vulnerability assessment. 1. Introduction Poland is situated in the central part of Europe and its northern border, which is about 500 km long, lies on the southern coastline of the Baltic Sea (Fig. 1). Intensive socio-economic transformation as well as the continuous development of tourism, recreation and related services together with more intensive exploitation of marine resources have increased the role of the Polish coastal zone. Almost all of Poland s territory (more than 99%) lies in the catchments basin of the Baltic Sea. 54% of it belongs to the Vistula drainage area, 34% to the Odra and 11% drains directly into the Baltic Basin. Situated along the Polish coast are five nationally important ports (Gdańsk, Gdynia, Szczecin, Świnoujście). The big cities SWEDEN B A L T I C S E A BALTIC PROPER LATVIA LITHUANIA ESTONIA RUSSIA Pomeranian Gulf Gulf of Gdańsk RUSSIA GERMANY OdraRiver POLAND open coast (dune, sandy beach) lagoon and Bodden type SWINOUJSCIE Szczecin Lagoon KOLOBRZEG DZIWNOW SZCZECIN West MIELNO USTKA DARLOWO Central region LEBA East region SOPOT WLADYSLAWOWO GDANSK HEL GDYNIA ELBLAG AREA I region AREA II AREA III - area of risk of flooding RUSSIA km Fig. 1. Location of the study area.

3 Vulnerability of Poland s Coast to Sea-Level Rise 133 Gdańsk, Gdynia and Szczecin, are regions of significant industrial, economic and cultural importance. Many harbours, shipyards, big industrial firms (e.g. refinery and chemical factories) and research centres are located there. Dunes and sandy beaches occupy most of the Polish open coast while cliffs are approximately 100 km long. Coast barriers between the sea and lakes are well developed in the central and eastern parts of the coast. The Hel Peninsula, a narrow spit separating the Gulf of Gdańsk from the open sea is under intensive erosion and flooding during severe storm surges. Poland s coastline forms two major gulfs the Pomeranian Gulf and the Gulf of Gdańsk, and two large lagoons connected with the sea by narrow straits the Szczecin Lagoon and the Vistula Lagoon. Because of its diversity, Poland s coast has been divided into three Areas (Fig. 1). Area I covers mainly the Odra Estuary, Area II western and central-east dunes, cliffs and open sea barrier beaches including Hel Peninsula, and Area III the Vistula Delta. Area I includes also the agglomeration of Szczecin and Świnoujście, while Area III encompasses Gdańsk together with Sopot and Elblag. The areas were chosen to reflect the major geographical and economic differences along the Polish coast. Climatic conditions in the Baltic Sea region, including Poland, are mainly subject to influences of the masses of wet air from the Atlantic Ocean and dry continental air masses from eastern Europe. Intensive movements of baric pressure fronts and related frequent changes of wind speed and direction have considerable influence on the climate typical of the South Baltic coast. Since Poland is distinctly affected by the global tendencies of climate change, the realistic quantity for the Polish conditions in the 21st century is the predicted global increase of temperature in the range of C/decade [Velinga and Leatherman, 1989]. Discrepancies between forecasts of the increase of the average temperature on Earth lie result, among many things, from the fact that none of the existing models is capable of reproducing all factors which substantially affect the climate and which are frequently random and highly non-linear. No matter the estimated rate of climate change, it should be expected that the above changes would produce the changes in precipitation, evaporation processes, frequency and intensity of pressure variations, wind climate patterns, as well as storm conditions and the severity of storms. In the Baltic region, the intensification of coastal erosion, land flooding and the frequency and severity of storm conditions has been observed in the past couple of years [Majewski et al., 1983, Blomgren, 1999, Orviku et al., 2003]. 2. Polish Coast 2.1. Hydro- and morpho-dynamic characteristics With an area of about 415,000 km 2, the Baltic Sea is a relatively small sea, linked with the North Sea by narrow and shallow Danish Straits. Therefore, it is practically non-tidal (tides about 6 cm high). The Baltic Sea is shallow along the Polish coast,

4 134 Z. Pruszak & E. Zawadzka Fig. 2. Number of days per year (with wind V 21 m/s) recorded at Kullaberg, South-western Sweden, since 1941 (after Blomgren, 1999). its salinity is low and is slowly decreasing. Presently, it equals 6 8 PSU (10 PSU at maximum). The long-term changes in salinity, sea-level rise or increase in the number of stormy days could be treated as one of the most significant physical indicators of the environmental change together with climate change. An example of variability of one indicator of this type, i.e. the frequency of stormy days measured in the western part of the Baltic Sea (Southern Sweden), is shown in Fig. 2. Winds in the South Baltic region mostly come from the west or south-west direction. Wind speed is seasonally variable. On the coast, the most violent winds occur during the autumn-winter months. In this period, the wind speed can exceed 25 m/s, while the long-term monthly average wind velocity amounts to about 6 8 m/s. In recent years, an intensification of changes in atmospheric circulation in the Baltic has been observed, which results inter alia in the increase of intensity and frequency of storms coming from north-west direction. Wave motion in the South Baltic is strongly related to wind surface waves or post-storm swell. Due to limited fetches, small water depths and rapidly changing pressure systems, they are short-period waves. The maximum height of significant waves (H s ) in the coastal zone measured by wave rider (at the depth of about 20 m) attains almost 4 m and the maximum period is up to 6 8 seconds. The monthly average significant wave height (H s ) mean can reach about 1.5 m (October 1996). Most frequently, the wave period varies in the range of 4 6 seconds, [Pruszak et al., 2000]. Due to the largest fetch, the highest and most dangerous waves and storm surges are produced by the north and north-east winds. These occur, however, much more rarely than winds and waves from the west and north-west, which are predominant in the South Baltic. The 100-year design water level, in spite of certain

5 Vulnerability of Poland s Coast to Sea-Level Rise 135 [m] 2.0 STORM SURGES HEIGHT Świnoujście Gdańsk Władysławowo return period T [years] probability of occurrence Fig. 3. Estimated sea water level exceedance curves for selected points on the Polish coast. Table 1. Sea-level rise for selected Polish stations. Station Increase Rate Increase Rate [mm/yr] [mm/yr] Świnoujście (west border) Kolobrzeg Ustka Hel 1.7 Gdańsk Tolkmicko (east border) 1.5 variability along Polish coast (Fig. 3), was assumed for the entire Polish coast as one mean value equal to 150 cm above MSL. This value has been assumed on the basis of measurements of changes of water table in the sea taken a few times a day (in the years ) and their statistical analysis at three selected points on the Polish coast [Majewski, 1990]. Long-term annual sea-level rise results from the superposition of numerous factors e.g. geologic, meteorologic, hydro-physical, which occur at various spatial and temporal scales. Sea level has been measured at various places along the Polish coast for many decades and the data for selected Polish stations are presented in Table 1. Column 2 presents the average values of sea-level rise in the period of the last 100 years (four stations), while column 3 shows the average sea-level rise in

6 136 Z. Pruszak & E. Zawadzka GDANSK USTKA SWINOUJSCIE approximating curve: Eq. (1) H [cm] year Fig. 4. Long term sea level rise for years and the forecast for future. the second half of the last century (six stations). Long-term sea level variation determined by average annual changes registered at three Polish stations during the last century (in the period ) are shown in Fig. 4. Considering the above mentioned data and assuming that the accelerated sea-level rise (observed in recent years) will be characterized by a similar gradient also in this century, one could define the empirical function of the forecast sea level change (H) in time (t). It has been established that this tendency would be best described by means of the following polynomial: H = (t t o ) (t t o ) 2 (1) where the correlation coefficient is R = 0.64 and the parameter t o = 1, 883, which mathematically defines the beginning of the function, physically constitutes a starting point (year) for observation and further forecasting. Taking into account the above function we can assume, for example, that the sea level in the Baltic will rise by around 20 cm by 2050 and even by 50 cm by 2100 when compared with the year Indeed, both the function and the values of the sea-level rise related to it should be treated only as an approximation. This results from the fact that the observed gradient has been considered as a representative for the whole century. Its value, however, depends on many factors, which are difficult to predict, and thus it can be different than the calculated one.

7 Vulnerability of Poland s Coast to Sea-Level Rise 137 Table 2. Main coastline data and protection measures. Main Coastline Data Total length of the coastline (km) 843 Total land area (km 2 ) 312, 685 Length of open coastline, i.e. wave exposed (km) 430 Length of sheltered coastline i.e. estuaries, lagoons, enclosed bays, etc. (km) 413 Length of dunes and sandy beaches 358 Cliffs 102 Coastline Protection Measures Total length of protected coastline including lagoon dykes (km) 316 Length of hard protected coastline, (km) including light and heavy revetments 41 and groins 98 Length of soft protected coastline (km) 56 Taking into account both the present global sea-level rise forecasts [Mimura and Harasawa, 2000; Nicholls and Mimura, 1998], and the function (1) approximated for the South Baltic Sea conditions, it can be estimated that the sea-level rise of cm is probable up to the year This estimate lies between the 100-year sea-level rise scenarios used with the IPCC Common Methodology (IPCC CZMS, 1922), i.e. between the values of 30 cm (optimistic scenario) and 100 cm (pessimistic scenario). Two major riverine systems exist on the Polish coast the Odra River to the west and the Delta Vistula River to the east, respectively 700 and 850 km 2 in area. A substantial part of the Vistula Delta, Żu lawy, is a depression reaching almost 2 m below sea level. The Żu lawy depression is the most important polder complex in Poland, consisting of 122 polders measuring 1,200 km 2, a large number of dykes, 125 automatics pumping stations as well as irrigation and drainage facilities. At present, the pumping stations are capable of pumping out enough water to let the water level fall by mm/per day. The work time of pump stations at full efficiency is days a year. General information about the Polish coast protection measures are listed in Table 2. The formation and character of Polish shores are generically associated with the last glacial period and the phases of development of the southern Baltic Sea. The coastal sections composed of Pleistocene sediments form cliffs of varying activity. Coastal lakes occupy Pleistocene depressions and they are cut off from the sea by spits. Low land shores are developed at the mouth of ice-marginal valleys and the border of the Gulf of Gdańsk and the open coast. These are predominant in the Vistula Lagoon and Odra Lagoon. Erosion processes of cliffs, such as landslides, slips and falls, result in the cliff s retreat. Average erosion of dune/cliff foot and of

8 B A L T I C S E A 138 Z. Pruszak & E. Zawadzka AREA II P O L A N D AREA III AREA I Legend - cliffs Fig. 5. Changes of coastline position for year

9 B A L T I C S E A AREA I AREA II P O L A N D Fig. 6. Changes of coastline position for year AREA III Legend - cliffs Vulnerability of Poland s Coast to Sea-Level Rise 139

10 140 Z. Pruszak & E. Zawadzka the general shoreline indicate a gradually increasing intensity of coastal processes, which will be intensified in the future due to the accelerated sea-level rise. Long-term observation of the open sea shoreline changes (Fig. 6) indicates that the average rate of coastal retreat during the last 100-year period was 0.12 m/yr [Zawadzka, 1999]. Investigation covered over 400 km of dune and cliff coastline of the non-tidal sea. In all 27,000 cartometric measurements were made. The basic cartographic material used were 1:25,000 maps coming from the end of the 19th and the beginning of the 20th century. These maps were then compared with the maps from the years The analysis of coastal changes was also based on 1:2,500 maps and the analysis of photo interpretation of 1:5,000 charts for the period The collected material forms a basis for the evaluation of the coastline and dune/cliff foot changes in the years and Cartographic measurements were made on the maps, which facilitated evaluation of changes of the coastline and dune/cliff foot. German basic maps in scale 1:25,000 (Messtischblatter), made in , topographic maps published by Military Geographical Institute in the years and maps from the last decades were analysed [Zawadzka, 1992, 1994, 1999]. The method of cartometric measurements consists in measuring the value of displacement of coastline and dune/cliff foot at fixed points along the coast. The general principle was to find common reference base from which the position of the analyzed morphological lines was measured. Cartographic materials were compared only within each type of maps, i.e. no cross-type analysis was performed. Cartometric measurements on 1:25,000 maps were made at 1,008 points, set 500 m apart, with some additional points situated at characteristic bends of coastline appearing on the contemporary map. The position of measurement points was determined on the newest map in the 65 system. Measurements on maps of the technical belt were made from common base sheets of separate periods or on blueprint of original charts, using a m quantification step [Zawadzka, 1999]. During the period (Fig. 6) the average rate of coastal retreat was 0.5 m/yr, and during the period it reached 0.9 m/yr. Erosion extended over increasing lengths of coastline: in the 100-year period 61%, in the 24-year period 72%, and in the 13-year period 74%. The dune/cliff foot eroded less intensely than coastline. In the period , the dune/cliff foot line retreated at a rate of 0.16 m/yr and in the period at 0.3 m/yr. The process of transformation of the coastal zone proceeded simultaneously with erosive and accretive processes. Analysis of changes of land area showed a decrease in the reconstruction of eroded beaches and dunes. In the 100-year period, reconstruction of eroded land encompassed over 69% of the destroyed area, in the period it was 20%, and in the period , only 14%. These data clearly document that processes of erosion are strengthening [Zawadzka, 1994, 1999]. These processes are now present over about 74% of the length of the Polish part of the Southern Baltic coastline. Between , about 55% of the surface of eroded dunes were naturally rebuilt, between only 47%. Processes of

11 Vulnerability of Poland s Coast to Sea-Level Rise 141 erosion and accretion proceeding at dune foot are also a significant indicator of the increasing erosive trend along the Southern Baltic coastline. In general, coastline and dune/cliff foot changes seem to be closely related. Between , about 70% of the investigated coast changes of both these lines showed a similar trend. The spatial and temporal differentiation of hydrodynamic factors results in spatial variability of coastline evolution and changes of coastal forms. In effect, alternating erosion and accumulation are observed. Spatial analysis of these processes allowed us to determine the structure of the coastal system, in which the basic elements are formed by stretches with opposing morphodynamic trends. Three classes of stretch length with varying trends of erosion or accretion were discerned. Class I are stretches of at least 4 km in length, class II 2 4 km, and class III less than 2 km. Analysis of lithodynamic processes within each of these classes made it possible to obtain some insight into the spatial structure and hierarchy within the erosion accretion system of the South Baltic coast. The basic elements of the system are sequentially arranged erosion and accretion stretches of various length. Higher levels of the structure are formed by bistructures, systems of bistructure and subsystems. The principle of alternation of erosion/accretion processes is confirmed for each of the investigated time segments and for each level of the system. With their number and extent, length Class I (length at least 4 km) erosive and accretive stretches play the most important role in the balance of sediments. The analysis of coastal changes in the erosion/accretion bistructures (pairs of alternating erosion and accretion stretches) which are formed by Class I and II stretches (2 4 km) once again shows that in the last years erosion has been strengthening along the Southern Baltic coast. The average rate of change within Class I and II erosion/accretion bistructures was 0.01 m/yr, in the period , it was 0.46 m/yr, and for , it increased to 1.12 m/yr. The basic structural elements of that system, i.e. Class I erosion stretches, or morphologic elements, such as spits and cliffs, are subjected to increasing erosion. This work presents the prediction, developed on the basis of the results for three scenarios of sea-level rise. It indicates that the erosive trends along the Southern Baltic coast will continue to rise. The increase of (in) the rate of coastal changes is related not only to the rise of an average sea water table over the last decades but also to the growing number of storms from the north-west sector Coastline protection Various types of coastal protection structures are present along 26% of the Polish coastline (Fig. 7). About 98 km of the coast is under the influence of groynes, while 41 km are protected by light and heavy revetments. The Hel Peninsula is protected along 34% of its length. An especially high level of coastal protection exists in two morphodynamic regions in the Jaros lawiec-świnoujście part of the Polish

12 Pomeranian Gulf 410 SWINOUJŚCIE 420 Szczecin Lagoon G E R M A N Y BORNHOLM 380 DZIWNOW WOLIN ISLAND AREA I SZCZECIN AA TRZĘSACZ NIECHORZE USTRONIE 330 MORSKIE KOLOBRZEG 300 MIELNO 290 KOSZALIN Wieprza River DARLOWO 240 Threatened areas USTKA SLUPSK 210 ROWY Lebsko Lake Gardno Lake L E G E N D From to +2.5 m above MSL From 0.0 to m above MSL Depression Inland waters Active cliffs Non-active cliffs Revetments Built-up areas Harbours Fishery wharves Piers Groins Kilometres Natural value in Europen scale 230 Kopan Lake AREA II 190 Łeba LEBA Sarbsko Lake Leba River Flooding threats WLADYSLAWOWO PUCK Reda River GDYNIA SOPOT VISTULA DELTA (Zulawy Polders) JASTRZEBIA GORA GDANSK Threatened regions River mouths and inlets of coastal lakes P O L A N D HEL Gulf of Gdansk KĄTY KRYNICA 20 AREA III Sambia Peninsula R U S S I A 0 PIASKI ELBLAG FROMBORK 142 Z. Pruszak & E. Zawadzka Fig. 7. Flooding threat for Polish coast and coastal protection measures.

13 Vulnerability of Poland s Coast to Sea-Level Rise 143 open coastline coastal defense structures are built along 71 km of the 126 km long coastline. Since the mid-19th century up to the present, the coastal defence systems have been continuously being developed, which indicates that these areas were particularly affected by marine erosion. The eroded cliff coasts and low land to the east of the ports were protected owing to the risk of sliding or flooding. Local coastal erosion was induced by the development of small ports of the western coast and by the contemporary transgression of the sea. Since the beginning of the last century until the 1940s, groynes were mainly used and some light and heavy revetments were built. However, as it has been observed that groynes and revetments are not fully effective, these methods of coastal protection in Poland are now much less used. At the end of the 1970s, artificial nourishment was introduced and is often used now. Because of their influence on neighbouring coasts, the coastal defence systems have to be extended still further along the shore, or additional defence must be built (revetments, seawalls, rubble mounds, nourishment in already protected areas). The necessity of further development of coastal defence systems in the regions located very far apart may even suggest the importance of some primary factor, probably Baltic sea-level rise. Sea-level rise is a major cause of increased erosion, which locally reaches the level of a coastal disaster, especially along stretches with a thin sediment cover. The initially short erosion bays, which were filled up with groynes and revetments, quickly developed eastwards of the ports Ko lobrzeg and Dar lowo at an average rate of 0.15 km/yr. Evaluation of the coastal changes in the period within groyne systems downstream of ports, showed a 4 times higher rate of retreat (0.36 m/yr) than the overall mean rate for the 100-year period. The rate of retreat was 2.5 times higher (0.21 m/yr) than the 100-year mean within groyne systems not connected to port areas [Zawadzka, 1994]. Because of great geographical differences along the Polish coast, the diversity of coastal features and the coastal vulnerability to sea-level rise (as it has already been mentioned), the whole Polish coastal zone has been divided into three main areas (Fig. 1). In this division Area I comprises 607 km 2, Area II 437 km 2, and Area III 1,233 km 2. The values given above represent the land situated below +2.5 m MSL (ASLR2), [Zeidler, 1992; Rotnicki et al., 1995; Pruszak, 2000]. 3. Vulnerability to Sea-Level Rise 3.1. Main studies and boundary conditions There is a 10-year history of vulnerability assessment in Poland. The first assessment studies of vulnerability of Polish coastal area to sea-level rise were completed in 1992 and this programme was called VA 92 [Zeidler, 1992]. The second comprehensive research programme VAAP 95 was carried out in 1995 and was one of the component of the US Climate Country Study Program USCSP Poland. This programme has

14 144 Z. Pruszak & E. Zawadzka included feedback from other USCSP components, created a set of new requirements and boundary conditions and also has taken into consideration a number of physical and socio economic developments in Poland during the years [Zeidler, 1997]. The VA 92 programme was based on the seven-step Common Methodology derived from IPCC [IPCC CZMS, 1992]. The VAAP 95, using similar method to Common Methodology re-assessed the Polish sea-level change trends, include recent data for annual sea-level maxima, storm surges and flooding probabilities for the Polish coast and updated a set of prices and socio-economic estimates. In the Polish vulnerability assessment studies, two global sea-level rise scenarios 30 cm (ASLR1) and 100 cm (ASLR2) by 2100 and two additional ones 10 cm (SLR1) and 30 cm (SLR2) by 2030 have been assumed as boundary conditions for the entire Polish coast. Taking into consideration the above sea-level rise scenarios, three impact zones have been selected. The selection of the impact zones was based on the extent of the sea-level rise assumed +0.3 and +1.0 m plus possible flooding due to storm surges (1.5 m), which gives the maximum inland boundary of +2.5 m above MSL (Pruszak, 2000). Thus the value +2.5 m represents the contour line which can be reached by occasional flooding due to storm surges with a return period of 100 in the case of ASLR2 (Fig. 8). On the basis of the maps scaled 1:25,000, the regions of natural units (of variable quality) threatened by sea flooding have been delimited within the contour lines m above sea level. The analyses and the resulting relationship between the coastal resistance, erosive processes and flooding threat allow us to predict the scale of erosive threat. This also enables us to prepare the overall classification of both +250 cm 150 cm (100 yr storm surges) +100 cm by 2100 yr (ASLR2) 150 cm (100 yr storm surges) +30 cm by 2100 yr (ASLR1) present sea level Impact zone I (0-30 cm) Impact zone II ( cm) Impact zone III ( cm) Fig. 8. Definition of sea level rise scenarios, boundary contours and impact zones for Poland s climate change coastal studies.

15 Vulnerability of Poland s Coast to Sea-Level Rise 145 Table 3. Inundation and risk in terms of impact zones for Poland s climate change coastal study area. Scenario Area Inundated Area at Risk ASLR1 Impact zone I (0 0.3 m) Impact zone II + III ( m) ASLR2 Impact zone I +II (0 1.0 m) Impact zone III ( m) flooding threats and shore resistance, as well as to estimate flooding threat of lagoons and the coastal zone. Taking into account the conditions of the Southern Baltic, three classes of shore resistance have been assumed. These classes consider morphological parameters and geological form. For the purpose of the shore resistance classification the basic parameters of the beach and the dune/cliff parameters have been determined. Each of these parameters have been assigned a particular class. The medium class of shore resistance has been calculated on the basis of 12 elements of the shore and beach morphology [Zawadzka, 1999]. The low resistance is characteristic of the lowland and dune shores of low parameters of the beach and dune. A medium resistance is typical for the dune shores of more than 5 8 m above the sea level and over m in width. A high (over 8 m) dune shores with beaches of over 50 m in width and cliff shores are marked for their high resistance. The classification of erosive threats has (have) been based on the calculation of the changes of (on) the shores in the last century. The small erosive/accumulative changes are m/yr, medium ones m/yr, and those of more than 1 m/yr are regarded as large [Zawadzka, 1999]. The shore resistance, when considered with regard to erosive threats and to the infrastructure imperilled by storm flooding, constitutes a sea-level rise. Inundated or lost areas, understood as the areas permanently inundated following the sea-level rise, have been marked as zone I at ASLR1 (30 cm/100 yrs) and zones I + II at ASLR2 (100 cm/100 yrs) (Fig. 8). The risk zone, which covers the regions flooded only temporarily (once a year at most) was defined as II + III at ASLR1 and III at ASLR2 (Table 3). On the basis of analyses, the shore segments of the highest and mean erosive threat have been identified. The shore segments with the lowest resistance and the highest erosive threat cover 208 km in total. Because of flooding threats and intensive erosion, about 175 km and 210 km, respectively should be subjected to investigation and protection in the nearest decade. The impact zones between contour lines m, m and m cover the area of F = 885 km 2, F = 1, 789 km 2 and F = 487 km 2, respectively, which is in total about F T = 2, 277 km 2, in addition to about F A2 = 50 km 2 of beach and dunes. These zones are likely to disappear as a result of ASLR2 and about F A1 = 20 km 2 due to ASLR1 [Pruszak, 2000]. Of course, the values F 0 0.3

16 146 Z. Pruszak & E. Zawadzka and F represent coast areas, which will be inundated and lost only by sea-level rise 0.3 m/100 yrs or 1.0 m/100 yrs, respectively, whereas beach and dune lost with values F A1 or F A2 will be caused by beach erosion due to the imbalance in sediment transport budget. The latter values were estimated separately taking into account new hydrodynamical and morphological conditions caused by the sea level rise equal 0.3 m and 1.0 m above present MSL, as well as the wave-current action Regional characteristics of inundation threats Area I The impact zones I and (I + II), and III within Area I measure in total about 168 km 2 and 497 km 2 and 110 km 2, respectively. The most substantial component to the surface area at stake is agricultural land. This results from the fact that sealevel rise will mainly affect low lying land adjacent to the Szczecin Lagoon and the Odra river mouth (Fig. 7). These regions, depending on sea-level rise and protective measures, can be degraded or totally flooded in the areas of considerable importance. The polders between east and west Odra, agricultural land around the Szczecin Lagoon, as well as urban and to a certain extent industrial-harbour regions such as Szczecin and Świnoujście are threatened mainly by flooding. The inundation risks in those regions are mostly related to high water levels of the lower Odra river during the early spring run-offs and backwaters resulting from storm surges in the Pomeranian Gulf. Even though the low areas within the m isohypses are protected with levees (east coast of the Odra Lagoon), the major part of the Wolin Island and the Świna Gate will be endangered in case of water-level rise of just 1 m. The land configuration in the vicinity of Dziwnów-Dziwnówek shows the beach (some 0.8 km 2 below a 1.25 m isohypse). The endangered infrastructure regions cover about 7.0 km 2, of which some 1 km 2 belongs to a category of more advanced infrastructure such as small fishing ports and tourism buildings. Open sea cliffs in the Area I are being destroyed at various rates, depending on storm intensity. However, this shore is considerably more resistant to destruction than dune and low land shore, so no particular measures are expected to be taken in those regions, despite their location in the National Park. Natural values of the eastern part of the Świna Gate and the Wolin Island are unique in European scale. In (On) the Wolin Island the area of 175 km 2 is at risk, of which 4% represent natural values of European significance. The region of the Pomeranian Bay east of the Wolin Cliff is endangered west of Miedzyzdroje. The contribution of the unique in Europe, wildlife areas in this region amounts to 7%. Most people threatened by permanent or temporary flooding, being in the impact zones II and III, live in urban regions (Table 4). The situation is inversed only in the case of the impact zone I.

17 Vulnerability of Poland s Coast to Sea-Level Rise 147 Table 4. Population of the study areas [thou]. Area Impact Zone Urban Rural Total I I (0 0.3 m) 1,630 3,450 5,080 II ( m) 21,080 9,630 30,710 III (1 2.5 m) 28,960 2,940 31,900 Total 51,170 16,020 67,190 II I (0 0.3 m) II ( m) 17,950 11,890 29,840 III (1 2.5 m) 5,920 3,370 9,290 Total 23,870 15,640 39,510 III I (0 0.3 m) 9,590 25,810 35,400 II ( m) 40,980 17,650 58,630 III (1 2.5 m) 33,080 11,030 44,110 Total 83,650 54, ,140 Total areas (I + II + III) 158,690 86, , Area II Generally, in the Area II there exists a chain of coastal barrier lakes. Narrow coastal barriers between the sea and low-lying lakes could erode, making the hinterland widely accessible to sea water. The higher level attained by storm surges in ASLR scenarios will destroy fore dunes and erode barrier islands and spits. The lowered barriers will then be susceptible to storm wash-over. The lakes will grow more saline. The Area II, is inhabited by much smaller population (particularly the urban one) and also is much less prone to flooding than the Areas I and III (Table 4). The western part of Area II is featured by the medium rate of erosion and low infrastructure. This area may be subject to flood risks in conditions of gradual SLR. Additional threats can be posed by rapid early spring run-offs. The classification of threats to the shore west of Lake Jamno indicates erosion of at least medium rate (Fig. 5). The resistance of shore to erosion in most of this region is rather low. In the presence of either important infrastructure or high natural values, all the depressions located in the hinterland of heavily eroded dunes take priority for protection measures. The regions east of the town of Ko lobrzeg have low resistance. These stretches have infrastructure at medium and high level and thus they are within protection priorities. The regions exposed to floods in the lower section of the Parseta river on the west of Ko lobrzeg, in the hinterland of low, eroded shore, are also characterized by unique natural values and valuable infrastructure. On average, the risk of erosion of the middle stretch of Area II is medium. Gradual SLR poses the growing threat of inundation terraces of coastal lakes. The total surface endangered by flooding measures 40 km 2. Depression areas at the banks

18 148 Z. Pruszak & E. Zawadzka of Jamno Lake are characterized chiefly by low natural values though they can be very high in some parts of the region. The inundation terrace of Bukowo Lake is of unique natural value in Europe. The infrastructure in the area between Mielno and Dar lowo (Fig. 1) is medium. In this situation natural values would be decisive in any protection measures. The most endangered regions are located in the vicinity of lake Wicko inlet (east of the cliff at Jaros lawiec). Additionally, vulnerable areas can also be found along the whole stretch of low dunes at the lake Kopań spit and east of the town of Dar lowo. The erosion threat of the area at Dar lowo is medium. The infrastructure of the strip exposed to flooding around Dar lowo was included into the lowest category. The inundation terrace of the southern part of Lake Kopań Lake and eastern part of Lake Wicko (see Fig. 7), have European class natural values. For this reason, protection measures of the shore are worth considering. The narrowest dune strip is located at the Lake Sarbsko spit. Its monitoring should be established to enable us to take immediate actions to protect the shore at the Lake Sarbsko spit and avoid the inundation of urban areas of the town of Leba, whose economic value is important. The northern banks of Lake Sarbsko display unique natural value, and the rest of the banks is of utmost national importance. Low areas up to 2.5 m above sea level cover about 110 km 2, some 40% of it are the regions utmost natural value West of Leba, an area of 130 km 2, S lowiński National Park and the Leba dune field. This area being a memorable national landscape, encompasses water, swamps, sand and special ecological areas and is included in UNESCO s list of the world s Biosphere Reserves. The highest percentage (27%) of threatened Polish coastal natural areas, unique in Europe, are located in the region of the S lowiński National Park. The eastern part of Area II is situated along the beach segment between Leba and Gdynia. West of the W ladys lawowo Port up to Jastrzȩbia Góra the shore erosion threat is medium in relation to the classification carried out for the whole coast. Local protection priorities may result from the risk of value loss of assets situated upon the cliff at Jastrzebia Góra. Assuming the future investment safety limit of m from the cliff crest, the current plans of the cliff protection should be delayed for the time being. However, the cliff processes should be monitored. The Hel Peninsula, a fairly spit formation separating the Gulf of Gdańsk, is most vulnerable to erosion, and will become a smaller island if no protection measures are applied. At this moment the peninsula has the shoreline of 72 km in length and locally narrows to m. The erosion rate between was assessed as medium (0.5 1 m/yr). In the shore s western and central part its resistance potential is predominantly low, which results in high risk to the hinterland and its infrastructure. Under ASLR conditions, it will become necessary to secure undisturbed transport and retain the tourism and in some places natural values of the Peninsula s root and centre. This will require vast protection measures such as the beach nourishment and the second line of coastal measures e.g. local dikes.

19 Vulnerability of Poland s Coast to Sea-Level Rise Area III The total surface of the Vistula River Delta with an average population density of 145 people/km 2 covers an area of 2,320 km 2. It includes the major city of Gdańsk. Here there are serious potential flooding threats under further SLR. Much of this area is the agricultural land known as the Żu lawy polder district and covers 1,800 km 2 in which 1,600 km 2 is under arable cultivation (6% of Poland s agriculture area). More than 50% of this area belongs to the study Area III and due to local subsidence it could be seriously affected under all SLR scenarios. Generally, about 64% vulnerable agriculture land is situated within Area III, versus 22% in Area I and 14% in Area II. In Żu lawy area, low natural values predominate. These occur mainly in the region of the Vistula Lagoon only, constituting respectively 2% and 7% of the unique values of European and national importance. Although the natural values of this region are low, its economic significance for Poland is substantial. Area III is the most vulnerable area in comparison to the others. Area losses under ASLR1 and ASLR2 are very heavy 672 km 2 (about 80% of all Area I III) and 948 km 2 (55%) respectively. The industry of Gdańsk (ports included) occupies 4.3 km 2 and 3.3 km 2 in impact zones I + II and III, respectively. The endangered urban areas of Gdańsk cover 4.5 km 2 and 7 km 2 in the same zones. Full prevention measures should be taken to avoid any loss of this area as it is invaluable not only for the Polish economy but also as a national centre of historical and cultural importance. The existing dykes will become too low under predict hydrological condition, especially ASLR2. The population to be relocated due to the sea-level rise (impact zones (I + II) is the highest in comparison with other specified areas (above 21% of the grand total). The number of people suffering from temporary flooding (not more often than once per year) is almost 38% of all the population of the study area (Table 4). The Vistula Spit features low and medium erosion threats. The lowest areas in the eastern sector of the Spit are fed by littoral drift from the Sambia Peninsula (Russia) (Fig. 7). The southern part of the Gulf of Gdańsk is characterized by high erosion risks that may contribute to the destruction of unique natural values in the vicinity of the river Vistula mouth. Gradual SLR will affect water levels, contribute to the rise of groundwater table in the lower part of the city of Gdańsk and inundation of depression areas on the west bank of the lower stretches of the river Vistula. 4. Potential to Adaptation to Sea-Level Rise Three Maritime Offices, located in Gdynia, S lupsk and Szczecin are responsible for the administration and technical protection of the seashore and the marine natural environment. They are dealing with the eastern, middle and western part of the Polish coast, respectively. Not only do they have to consider the current needs and potential dangers but also they are compelled to predict and prevent future threats.

20 150 Z. Pruszak & E. Zawadzka Table 5. Poland s coastal vulnerability to ASLR1 and ASLR2, after [Zeidler, 1997]. Impact Category Unit ASLR1 (30 cm/100 yrs) ASLR2 (100 cm/100 yrs) Retreat Full Protection Retreat Full Protection Capital value lost 10 9 US $ 6 28 People relocated < People at risk < < 5.8 Capital value at risk 10 9 US $ 40 < 5 18 < 5 Damage (salinity) 10 9 US $ < 0.01 < 0.01 < 0.01 < 0.01 Ecological area lost km Special area lost km Full Protection (FP) 10 9 US $ implement. cost Annual maintenance 10 9 US $ The analysis of erosive threats together with flooding threats for Poland, in the conditions of sea-level rise, showed the existence of the coastal regions variable in resistance, thus implying the need of further plans for shore protection. Two adaptation strategies, i.e. do nothing or Retreat (R), and Full Protection (FP) have been adopted and compared in physical and socio-economic terms as part of the vulnerability assessments already outlined. The last one was defined as the implementation of all feasible protection measures to avoid loss of any coastal land or value. Some results of the vulnerability analysis for these two major strategies and the classified areas (Fig. 1), are shown in Table 5 and Figs. 9(a), (b) and (c). In Figs. 9(b), the total capital value is the sum of the capital value of areas that would be lost and remaining under the risk of flooding. Full protection of the Odra estuary (Area I) means preservation of the polders on the periphery of the estuary. All polder dykes must be adapted to the projected situation, and many new dykes must be constructed. The dyke crest at present is 2 m above MSL of Szczecin Bay. This height takes into account the relative height of storm surges, run up and safety coefficient in the range of m. However, the height related to the sea-level rise has not been taken into consideration. According to the general Polish regulations, the dykes should be 70 cm higher than the 50- year storm (i.e. annual probability of 0.02). If the sea rises 30 cm, the water level during the 50-year storm will be too high to secure the area protected by dykes for a longer time and if the water rises by 1 m, the breach of dykes at least once a year is highly probable [Zeidler, 1992]. This will imply the necessity of raising the top of the dykes and in case of the newly built ones the constructions of the dykes at proper heights. What is more, wharves in ports and urban areas must be raised. New polders should be formed. In total, 107 km and 280 km of new dykes must be constructed in Area I under ASLR1 and ASLR2, respectively. The lengths of upgraded dykes are 243 km and 324 km. The cost of full protection in

21 Vulnerability of Poland s Coast to Sea-Level Rise USD AREA I II III (a) Full Protection Cost USD AREA I II III (b) Total Capital Value % 50 0 AREA I II III Protection Coast (c) Captial Value at Loss total capital value capital value at loss ASLR2 capital value at loss ASLR1 Fig. 9. Assessments of full protection cost, total capital value and ratio of protection cost to capital value at lost along the Polish coast. Area I is estimated between 0.5 billion US$ (ASLR1) and 2 billion US$ (ASLR2), i.e. generally less than 10% of the value (15 billion US$) of the lost property and land (all values and prices from the end of the 1990s). To protect the most important places in Area II, new polders and new facilities such as pump stations, drainage and other infrastructure are required, while older polders must be redesigned. Full protection of coastal lakes can be secured by containing them within dykes of adequate height and impermeability. The construction

22 152 Z. Pruszak & E. Zawadzka of new or upgraded dykes around lakes (and their rivers as well) should be connected with adequate protection of the seaside. Finally, the full protection option for Area II embodies the construction more than 200 km of new and about 290 km of upgraded dykes under ASLR2 and 75 km and 260 km under ASLR1, respectively. These dykes partly belong to coastal lakes and partly to rivers protection system that guards the adjacent low lands. A substantial part of the Area III will be endangered by ASLR impact. In this area, the most important polder complex of Poland (Żu lawy polders) is situated. Full protection of Żu lawy polders at ASLR2 requires a bulk adaptation of existing dykes and the construction of some new dykes as well as storm and flood prevention facilities. At ASLR2, one should construct 52 km of new dykes and upgrade 647 km of those presently in use. Under ASLR1, the respective numbers are 13 km and 600 km. A substantial part of the urban area of Gdańsk is in the hazard zone under ASLR and should be protected. The detailed analysis of costs implies that the action should be taken first on the coastal segments adjacent to Gdańsk and Szczecin, where vast agglomerations are located, with concentrated industry and related infrastructure, as well as scientific and cultural centres. Moreover, in the future, one should carefully consider the boundaries for safe investments on cliffs and spits threatened by erosion. The continuous monitoring will be necessary on the most threatened coastal segments and on the segments associated with the newest investments in the coastal zone, such as optical fibres and gas pipings. One of the important actions related to studies on the analysis of threats and SLR adaptation strategies of coastal areas in Poland is the incorporation of techniques of GIS-based analyses. Methods of this type prove to be very useful tools for various simulation studies on the areas subjected to potential inundation under a range of variants of ASLR. For a few selected sections of the Polish coast calculations and maps, threats and area loss are regarded as the function of various sea-level rise options. These simulations are performed in relatively small spatial scales and are treated as pilot, inception studies, aimed at developing adaptation strategies for the areas vulnerable to ASLR. The analyses and the resultant maps should provide potential for monitoring, in relation to the scale of ASLR, the inundated areas, a number of exposed households and important infrastructure, shore erosion plus material and environmental losses. 5. Discussion and Conclusions The existing scenarios of the increase in greenhouse gases concentration in the atmosphere, definitely indicate that a mean sea-level rise, associated with climatic change, is inevitable in the next decades. The resulting problem is how to minimize the undesirable effects of this process and how to resist against it. This concerns both technical aspects and others related also to the intangible values affecting human

23 Vulnerability of Poland s Coast to Sea-Level Rise 153 life. Determining when to initiate a firm protective actions and what should be their range is one of the most difficult aspects of human adaptation to sea-level rise effects. Because such activities are associated with big costs and because the exact rate of sea-level rise is still uncertain, the concept of monitoring climatic change and related sea-level rise has been initiated in many countries. Various scenarios of the above changes are being prepared and updated continually, their effects are projected together with selective shore protection planning and further development of the process is awaited. Poland is one of the countries that follows the above approach. The analysis of the South Baltic coastal changes in the last century reveals the intensification of erosive phenomena within all elements of the coastal system. These changes took place under conditions of sea-level rise at an average rate of cm/100 yrs. In recent decades, relative sea-level rise had greater speed. Besides, the occurrence of storm surges has become more frequent and this was associated to the changes in atmospheric circulation. These phenomena caused the intensification of erosive changes and the necessity of protection of affected shore segments. Till now, protective systems have already been developed in the area of over 26% of the south Baltic Polish coastline. In Poland, as shown by various research and analyses, more than 2,400 km 2 and 244,000 people are found to be vulnerable to the impact of sea-level rise. The total cost of land loss due to ASLR2 has been assessed at nearly US$30 billion plus some US$18 billion as a result of the risk of flooding, while the cost of full protection reaches US$6 billion (as estimated in 1995). Increasing prices urge for prompt protection actions. The analysis of natural patterns of shoreline variability indicated that the highest erosive threats are in the regions of the Vistula outlet segment, some regions between W ladyslawowo and Leba, as well as Leba-Ustka and also a few coastal segments situated westwards of Ko lobrzeg. Moderate threats pertain to Hel Peninsula, the entire central coast (AREA II) and most segments of the west coast. Assuming the increase of the length of eroded shore segments and analyzed scenarios of the sealevel rise, it should be expected that over 70% of the shore length will be subjected to moderate and big threats. We can expect that during the next decades the most threatened shore segments will be located in the Vistula outlet region and at many coastal segments of the central coast (AREA II). The remaining coastal segments could be classified as moderately or weakly threatened. The detailed analysis revealed that there are 24 Polish coastal regions in which high water levels can occur due to storms, gradual sea-level rise, as well as rapid flooding caused by precipitations. Depending on the configuration of river valleys, these factors will cause various regional threats. The greatest threats concern the lower Vistula valley, the lower Odra valley and vicinities of the coastal lakes. Smaller regional flooding threats occur at outlet segments of smaller rivers in the central part of the Polish coast (AREA II). Another reason to flooding threat is that, during