Beach Stabilization at Kołobrzeg, Poland

Journal of Coastal Research
SI
71
131–142
Coconut Creek, Florida
2014
Beach Stabilization at Kołobrzeg, Poland
Agnieszka Strusińska-Correia
Leichtweiß-Institute for Hydraulic Engineering and Water Resources
Department of Hydromechanics and Coastal Engineering
Technische Universität Braunschweig, Germany
a.strusinska@tu-braunschweig.de
www.cerf-jcr.org
ABSTRACT
Strusińska-Correia, A., 2014. Beach stabilization at Kołobrzeg, Poland. In: Silva, R., and Strusińska-Correia, A.
(eds.), Coastal Erosion and Management along Developing Coasts: Selected Cases. Journal of Coastal Research,
Special Issue, No. 71, pp. 131–142. Coconut Creek (Florida), ISSN 0749-0208.
www.JCRonline.org
The coastal erosion on the Baltic Sea at Kołobrzeg (Poland) is a result of the superposition of the local
hydrodynamics and the anthropogenic factors of this multi-functional, intensively developing city. Particularly
high rates of erosion are observed along the 3 km-long shore, east of the port, despite countermeasures
undertaken (groynes, seawalls, waveblocks and beach nourishment). In view of the increasing importance of
Kołobrzeg as a tourist resort and the investment boom taking place in the immediate vicinity of the shoreline,
the preservation of the disappearing beaches and protection of the low-lying urbanized areas became a burning
issue for the local authorities. However, the means of coastal protection applied have been ineffective and have
also impaired the natural beauty of the beach. The continuous submerged breakwater of length of almost 3 km,
constructed in 2010 - 2012, seems to have stabilized the beach, although its impact on the adjacent coastal
sections and environment requires further analysis. In this paper, the causes of the coastal erosion at Kołobrzeg
are discussed, based on the morpho-geological and hydrodynamic conditions as well as the character of the
urban development. The beach protection used is analyzed chronologically in terms of its effectiveness and
novelty.
ADDITIONAL INDEX WORDS: Coastal erosion, Baltic Sea, groynes, waveblocks, submerged breakwater.
____________________
DOI: 10.2112/SI71-016.1 received 5 March 2014; accepted in
revision 4 August 2014.
© Coastal Education & Research Foundation 2014
(City Kołobrzeg).
0
100 km
Elevation [m]
INTRODUCTION
The very attractive location and resulting favorable climate
gives Kołobrzeg the potential to become one of the most
important tourist destinations on the western coast of the Polish
Baltic Sea (Figure 1). The development of this city from a small
fishing port at the end of 1950, with an estimated population of
6,800, into a popular health resort and spa, with some 47,000
inhabitants, was conditioned by the availability of natural
resources and the favorable marine climate for disease
treatment. While the tourist boom on the Polish coast has
generally started in the second half of the 20th century, as the
country recovered from the World War II, Kołobrzeg had
already become famous for its brine baths at the beginning of
the 19th century, when it was a part of Prussia. Nowadays, about
27 sanatoriums, of which 23 are open all year, offer respiratory,
cardiovascular and joint diseases as well as metabolic disorders
treatments, combining the medical properties of brine/mineral
water springs, peloidbeds and fresh air (Miedziński, 2012 and
City Kołobrzeg).
Despite rather low sea temperatures (under 20° C on average
in summer) and a very short bathing season (June to August),
the number of tourists staying at Kołobrzeg has been increasing
constantly in recent years: 106,000 in 1995 and more than
double in 2008, of which about 36 % were international visitors
3 000
2 000
1 000
0
200
500
500
300
0
1 000
2 000
Figure 1. Location of Kołobrzeg on the Polish coast of the Baltic Sea
(map: http://www.eea.europa.eu/data-and-maps).
As well as the tourist and spa sectors, the seaport in
Kołobrzeg represents the second dynamically developing
132
Strusińska-Correia
_________________________________________________________________________________________________
54°12’0’’N
branch. The port, located at mouth of the Parsęta River, is used
for commerce and fishing; it has a marina and a ferry harbour. In
2006, cargo traffic was 157,600 t. In 2006, almost 19,000
international passengers passed through the port (Port of
Kołobrzeg). Constant expansion of the port and modifications of
the port entrance, including elongation of the jetties, have been
required to increase the operational capacity of the port.
As the tourism is of paramount importance for local economic
development, improvement of the tourist infrastructure and
tourist entertainment options, in particular the maintenance of
wide, sandy beaches, govern the development strategies of the
city. Kołobrzeg has already three sea baths, shown in Figure 2:
the Central and East Beach at the eastern coast and the West
Beach at the western coast.
East
Beach
a)
Central
Beach
Baltic
Sea
54°11’0’’N
D4
N N
KM 335
D2
54°10’0’’N
D5
D6
D7
N
KM 334
D3
D1
D13
D12
D10 D11
KM 328
D9
N
N N
KM 331
D8
N
KM 333
N
KM 329
KM 330
KM 332
Kołobrzeg
KM 336
0
KM 337
1 km
KM 338
15°30’0’’E 15°31’0’’E 15°32’0’’E 15°33’0’’E 15°34’0’’E 15°35’0’’E 15°36’0’’E 15°37’0’’E 15°38’0’’E
Old wooden seawall
Waveblock unit
Geotextile tubes filled with sand
N
Beach nourishment
Tetrapod unit
Submerged breakwater (including groynes)
Steel/concrete seawall with reinforced cap
Roubble mound revetment
Figure 2. Coastline at Kołobrzeg: (a) with existing coastal protection
structures and kilometrage (KM) according to Maritime Office (after
Marcinkowski and Ossowski, 2008; map courtesy of T. Marcinkowski,
Maritime Institute in Gdańsk); (b) aerial view from 29.08.2012, the wide
beach between pier and Kamienny Szaniec (the East Bulwark) after
nourishment performed in June - October 2012 (Google Earth).
The East Beach, 150 m long, is located in the Podczele
district between KM 327.0 and KM 328.0 (where KM denotes
the kilometrage defined by the Maritime Office); the Central
Beach, 750 m long, at the river mouth (between KM 333.0 and
KM 334.0) and the 350 m long West Beach, west of the port
(between KM 335.0 and KM 336.0) (Sea baths in Kołobrzeg).
Only the West Beach does not require stabilization and thus it
has preserved its natural character. However, due to its
unfavorable location (on the other side of the city), it is not as
popular among the tourists. The other two beaches lie in
a coastal section that has been strongly modified by both
intensive human activities and local hydrodynamic conditions.
As a result of the occurring erosion, these beaches would have
almost disappeared, if it were not for the repeated beach
nourishment work carried out since 1982.
The range of coastal protection structures at Kołobrzeg
consists currently of a very dense network of "hard" and "soft"
countermeasures (e.g., groynes, seawalls, waveblocks, tetrapods,
beach nourishment and biotechnical methods), established over
many years to stabilize the beaches and to protect the city
against flooding. This unique system illustrates the historical
development of coastal engineering in this region, as it includes
old groynes built at the beginning of the 20th century by the
Germans (the remains were replaced in 2010 - 2012 during the
construction of a submerged breakwater), typical structures
constructed in Poland between 1980 and 1990 as well as more
innovative means of protection such as waveblocks and
the submerged breakwater. The increasing number and the
variety of the coastal protection structures at Kołobrzeg indicate
their ineffectiveness and result most probably from a poor
understanding of sediment budget and local hydrodynamics.
In this paper, the advantages and disadvantages of the beach
protection measures, applied at Kołobrzeg over the last 150
years, are discussed under the consideration of the type and
historical evolution of the factors influencing the local erosive
processes.
CHARACTERISTICS OF THE STUDY AREA
Bathymetry and Geomorphologic Conditions
Kołobrzeg is located in the middle of the coast of the West
Pomeranian Voivodeship, between the Słowińskie and
Trzebiatowskie Coast (see Figures 1 and 2). Due to the lowlying and swampy character of the area, on which the city is
built (about 3 km2 of its urbanized part lies only 0.0 - 2.5 m
above mean sea level), as well as its proximity to the open Baltic
Sea, the city is highly prone to flooding, which is likely to
intensify by the rising sea level due to global climate change
(e.g., Zeidler, 1994 and Cieślak, 2007). The substratum in this
area is formed by deep layers of glacial till with accumulations
of alluvial - peat material above. The till layer occurs very close
to the surface at the western beach (ca. 0.2 m below mean sea
level), while the peat layer occurs directly below the dunes. Both
layers are very often uncovered during heavy storms by washing
away of the upper sandy layer (Łabuz, 2003; Łabuz and
Łuczyńska, 2010).
The Parsęta River, dividing the city into a western and eastern
part, has determined the convex shape of the coast at its mouth
through sediment accumulation. This cone-like shore, stretching
from km 331.5 to km 337.0, as shown in Figure 2, has produced
a shoreface platform that is ca. 1.5 km wide, 550 m long, 4 - 5 m
deep with very steep slopes (up to 1:15) at the seaward side
(Marcinkowski and Ossowski, 2008).
Kołobrzeg lies partially on an area originally covered by a
dune system which has been heavily modified by human
intervention over a long period, (i.e. urban growth, harbour
expansion, tourism, military and coastal protection structures) as
well as by severe storms (Figure 3). A system of well-preserved
dunes protects the natural, relatively wide sandy beaches (on
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Coastal Beach Stabilization at Kołobrzeg, Poland
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average 35 m) stretching for 3 km west of the Parsęta River. The
swampy area at the extreme west of this dune system, together
with the existence of a military area behind, prevents any tourist
development here.
a) West coast of Kołobrzeg
D1: High, natural, blown out dune ridge. Dunes
evolve into swampy area to the west. Military
area at the back. Numerous beach entrances.
D2: High, natural dune ridge. Buildings of tourism
purposes at the back. Numerous beach
entrances.
D9: Badly abraded dune protected by seawall
made of waveblocks. Boardwalk on the top/back.
D10: Fully abraded dune, land protected by
concrete seawall and tetrapods. Boardwalk on
the top.
D11: Abraded ridge protected by tetrapods.
Boardwalk at the back.
D12: Abraded dune, beach stabilized by roubble
mound with fascines on geotextile (covered by
sand). Bunker on the slope, boardwalk at the
back.
D13: Only narrow dune ridge separating beach
from the swamp at the back.
D3: Very high, natural dune ridge. Bunker
remains on the slope, military area at the back.
Dune grass
Salix shrub
b) East coast of Kołobrzeg
D4: Dune protected by sheet pile wall/concrete
seawall with geotextile bags filled with sand.
Boardwalk on the top.
D5: Seaside dune slope covered by wide stairs,
terrace and hotel on dune ridge.
D6: Small dune ridge protected by fence against
tourists, boardwalk on the top.
D7: Narrow dune ridge, abraded slope protected
by old wooden fence and younger sheet pile wall.
Boardwalk on the top.
D8: Badly abraded, then regenerated dune
protected by concrete seawall. Boardwalk on the
top.
Concrete seawall, sheet pile wall
Tree
Wooden fence
Geotextile bag filled with sand
Building
Tetrapod unit
Bunker remains
Waveblock unit
Boardwalk
Roubble on fascine
Figure 3. Anthropogenic modifications along: (a) west coast; (b) east
coast of Kołobrzeg (dune profiles after Łabuz, 2003, sketches courtesy
of T. Łabuz, University of Szczecin; photos of D4 - D6, D9 - D11, D13
courtesy of M. Burdukiewicz, Maritime Office in Słupsk; photos of D7 D8 courtesy of B. Zabłocki, Port of Kołobrzeg).
Generally, the dunes are wide, high and healthy (particularly
in sections D1 and D3; the latter of height of 8 m a.s.l. over a
distance of approx. 1.5 km), apart from the central part (D2)
where a low, narrow dune ridge has evolved (see Figures 2a and
3a). The entire west dune system is naturally stabilized by
vegetation: on the landward slope and over the ridge mostly by
oaks and, on the seaward slope, by downy mountain willow and
grass (Łabuz, 2003 and 2005; Łabuz and Łuczyńska, 2010). In
contrast, the sandy beaches east of the Parsęta River are very
narrow and lower than in the western part, reaching on average
2.5 - 4.8 m a.s.l. Dunes have almost disappeared over a distance
of 2 km (Figures 2a and 3b) as a result of: (i) erosion caused by
unfavorable local hydrodynamic conditions (higher waves
approaching the shore as a result of deepening of the foreshore
by strong waves reflected from the seawalls, generation of
strong rip currents transporting the sediment towards the open
sea), (ii) strong urbanization taking place on and behind the
dune ridges, aiming at the increase of the attractiveness of the
Journal of Coastal Research, Special Issue No. 71, 2014
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Strusińska-Correia
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city (i.e. construction of footpaths, restaurants, hotels, etc.), (iii)
construction of the structures protecting the urbanized hinterland
against flooding and erosion. The dune ridge has been affected
by human activity particularly at the port entrance and at the
Central Beach. Moreover, there is a boardwalk/bike path along
the coast between the port and the Podczele district. The only
intact, vegetated dune sections are at D6 and D13 (Figures 2a
and 3b). A 200 m wide green belt, with numerous footpaths,
separates the beach from the urbanized area concentrated
between KM 331.5 - KM 333.3 and KM 330.0 - KM 330.6 (see
Figure 2b). Around 4 km east of the river, a swampy, marshy
area begins behind a narrow, low dune (Łabuz, 2003; Łabuz and
Łuczyńska, 2010).
The sea bottom consists of glacial till and silt with a thin
dynamic sand layer of varying thickness and origin in both
western and eastern sections of the coast. West of the harbour
the sand of diameter of d50=0.149 - 0.304 mm, originating from
the sediment exchange on the shore, accumulates as a dynamic
layer of between a few centimeters and 2 m. In contrast, the
dynamic layer in the eastern part of the coast is very thin or
absent and made up of finer particles of d50=0.150 - 0.214 mm
(Marcinkowski and Ossowski, 2008). These sand accumulations
come mostly from beach nourishment and, to a lesser extent,
from the erosion of the sea floor.
Climate Conditions
The Kołobrzeg climate is determined predominantly by the
influence of the Baltic Sea and is characterized by low
temperature amplitudes between mild winters and warm
summers. The maximum average temperature occurs from June
to August and does not exceed 20° C, while the minimum
average temperature of -1° C is recorded between January and
February.
a) Wind rose
P [-]
N
from the Southwest, West and South, as indicated by the mean
annual wind rose plotted in Figure 4a. The strongest winds,
causing severe storms, occur in January and come from the
North, Northeast and Northwest. On average, there are more
than 70 days with strong winds (i.e. of speed not exceeding 10
m/s) and about 20 days with very strong winds with speed up to
16 m/s (Borodziuk, 2008).
Maximum annual precipitation is around 675 mm; the highest
monthly rainfall (85 mm) occurs mainly in July, while the
lowest (more than 30 mm) occurs in February and April. There
is snow cover (maximum 0.2 m thick) for 40 - 60 days in the
year. Ice covers the sea from February to mid of March for up to
43 days but usually 7 - 15 days on average (Łabuz, 2005 and
Borodziuk, 2008).
Tide, Wave and Water Level Conditions
Conditions in the Baltic Sea are dominated by surface waves
(wind waves and swells), while the influence of tides can be
ignored, since the maximum tidal amplitude reaches only a few
centimeters (i.e. the sea is microtidal) (Furmańczyk, 2013).
A wave rose for the coast of Kołobrzeg, depicted in Figure
4b, represents wave heights generated at a water depth of 20 m
by the mean annual wind shown in Figure 4a. These results were
obtained using the quasi-spectral method developed by Kryłow
et al., (1976) due to the lack of in situ measurements (Zeidler et
al., 1995; Szmytkiewicz et al., 1998).
b) Wave rose
0.16
P [%]
0.12
0.08
N
10
0.04
0.0
Calm
+
~ 0.03 0.0 0.04 0.08 0.12 0.16
P [-]
0.16
0.12
E
P [-]
(4)
(1)
E
H [m]
0.08
0.04
V [m/s]
0 2 4
6 8 10
(1) 0 < H < 0.25 m
(3) 0.51 < H < 1.0 m
(2) 0.26 < H < 0.50 m (4) H > 1.0 m
Figure 4. Mean annual wind rose (a) and mean annual wave rose (b) for
Kołobrzeg (after Zeidler et al., 1995 and Web atlas of the Polish coastal
zone).
Two periods with different wind conditions can be
distinguished: spring - summer from March to October, with
winds coming from the sea with speeds of 2.5 - 3.5 m/s and
autumn - winter from September to February, with winds
coming from the land with speeds of 5 - 7 m/s, but sometimes
reaching more than 10 m/s. The majority of the winds come
Figure 5. Numerical prediction of hydrodynamics at Kołobrzeg for a
storm in October - November 2006: (a) significant wave heights; (b)
depth-averaged currents induced by waves (Marcinkowski and
Ossowski, 2008; figures courtesy of T. Marcinkowski, Maritime
Institute in Gdańsk).
Severe storms, characterized by high storm surges which are
responsible for the dune erosion, are recorded every 10 - 12
months (Furmańczyk, 2013). Distribution of significant wave
heights and wave-induced depth-averaged currents at the coast
Journal of Coastal Research, Special Issue No. 71, 2014
Coastal Beach Stabilization at Kołobrzeg, Poland
135
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of Kołobrzeg for a typical storm was analyzed by Marcinkowski
and Ossowski (2008) and is presented in Figure 5 for a better
understanding of the accompanying wave height/current
patterns.
The considered storm occurred between October 31 and
November 10, 2006 and was characterized by wind speeds of up
to 18 m/s, blowing from the East and turning towards the North.
Wave propagation and current patterns were obtained based on
simulations performed with the MIKE 21/3 model, for which the
offshore wave conditions were determined by means of the
WAM 4.5 spectral wave propagation model, using recorded
wave data. Under these storm conditions, waves of more than
3.0 m reached surf zone, within which their height subsequently
decreased as a result of the breaking process. As indicated in
Figure 5a, this pattern is repeated over the entire study area. The
current pattern differs in the eastern, middle and western parts of
the coast as illustrated in Figure 5b. Between KM 329.0 and KM
332.0 (the eastern part), a strong longshore current is generated
towards the West, with a speed of 0.5 - 0.7 m/s, in places
reaching 0.9 m/s. A weaker longshore current in the opposite
direction (i.e. to the East) exists between KM 333.0 - KM 334.0
(in the middle part). Between KM 332.0 and KM 333.0, these
two oppositely directed currents generate an offshore current of
ca. 0.3 - 0.4 m/s. Behind the western jetty, the current is directed
to the West and is characterized by a slight speed increase from
0.4 to 0.6 m/s between KM 334.6 and KM 336.0 (Marcinkowski
and Ossowski, 2008).
The current mean water level in Kołobrzeg ranges from 501
to 508 cm (zero at the watermark in Kołobrzeg corresponds to
504.4 cm) but the varying wave conditions due to alternating
wind and pressure oscillations, cause oscillations of the mean
sea level (even up to 3.4 m) as reported by Borodziuk (2008)
and Łabuz (2013). Particularly significant fluctuations of the
mean sea level, accompanying heavy storms, are normally
observed between October and February, with the lowest one of
376 cm, recorded in 1968 and the highest ranging from 527 to
716 cm (where 490 cm represents 0.0 m a.s.l.). Selected
historical storm surge records are shown in Table 1 with a
maximum of ca. 710 cm occurring in 2009.
Table 1. Exemplary records of recent and historical storm surges in
Kołobrzeg (Łabuz, 2012a and Port of Szczecin - Świnoujście).
Date
02.1874
1883 1899
1914
01.1983
11.1988
11.2006
01.2007
10.2009
Recorded water level (cm)
692
685
670
643
647 ca.
660 ca.
640 ca.
710
The probability of occurrence of annual maximum and
minimum sea level for Kołobrzeg is provided in Table 2, based
on the Gumbel distribution (Borodziuk, 2008).
Increasing mean sea level is a crucial issue for the flood
mitigation strategy of Kołobrzeg, since the city is located in a
low-lying area and the dune ridge has been successively
degraded. A larger intrusion of water into the Baltic Sea basin as
well as increase of both storm intensity and frequency are
considered as the most important results of the global climate
change for this region. Zeidler (1994) and Zeidler et al., (1995)
estimated the increase of the water level at Kołobrzeg as ca. 1.1
mm/year, based on long-term observations since 1867 (see
Figure 6).
Table 2. Probability of occurrence of annual maximum and minimum
water levels in Kołobrzeg (after Borodziuk, 2008).
Probability 99
90
80
70 50 30
20 10
Years
1.01 1.11 1.25 1.43 2.0 3.33 5
10
Max. (cm) 547 560 568 575 588 605 617 635
Min. (cm)
453 440 434 430 422 413 407 399
5
20
652
392
1
100
689
377
Zawadzka (1996) predicted similar changes in sea levels due
to global warming of up to 1.4 mm/year. Cieślak (2007)
postulated three different scenarios of the sea level rise
applicable to the entire Polish coast: (i) optimistic with the
increase of 3 mm/year, (ii) most probable with the increase of 6
mm/year and (iii) pessimistic with the increase of 10 mm/year.
Mean water level [cm]
500
Kołobrzeg
(1886 – 1985)
495
490
1855
1873
1865 1875
1885
1895
1905 1915
1925 1935 1945 1955
1965 1975 1985
Year
Figure 6. Measured 11-year mean sea level at Kołobrzeg (after Zeidler,
1994 and Zeidler et al., 1995).
Sediment Transport and Sediment Budget
According to Szmytkiewicz et al., (1998) and Boniecka et al.,
(2010) two directions of longshore sediment transport can be
distinguished at Kołobrzeg, depending on the water depth - in
smaller depths eastward transport is dominant and weak
westward transport occurs in larger depths, with zero net
longshore transport for water depth larger than 8.0 m. Thus, the
resulting westward longshore sediment predominates weakly at
Kołobrzeg, however strong local disturbances occur as
mentioned by Borodziuk (2008) and Boniecka et al., (2010).
A strong cross-shore sediment transport prevails at the coastal
section between the east jetty and the East Bulwark, as indicated
by the numerical results presented in Figure 5b.
Due to the mentioned deficit of the sediment at the sea bottom
and too small sediment supply (ca. 10,000 m3/year from the
Parsęta River and less than 100,000 m3 from beach nourishment
over a distance of 500 m on average), the sediment budget,
particularly in the region between the east jetty and the East
Bulwark, is negative. This has conditioned strong erosional
processes occurring in this coastal section.
EROSION ON THE KOŁOBRZEG COAST
Historical development of Kołobrzeg, accounting for
reconciliation of its multi-functional character (i.e. settlement,
Journal of Coastal Research, Special Issue No. 71, 2014
136
Strusińska-Correia
_________________________________________________________________________________________________
port, marine fortification, sea/health resort) as well as the
erosive character of the local coast are responsible for the
modifications of the shoreline. Kołobrzeg has been facing the
problem of erosion for a long time (compare Figures 7a and b)
as indicated by the building of groynes in the second half of the
19th century.
budget (low rate of longshore sediment transport, too small
volume of nourished sand used) hampered establishment of the
equilibrium at this coastal section.
1500
a)
Distance from reference line [m]
1450
1965
1969
1400
1973
1981
1350
1993
1300
1997
1250
Jetties
1200
1150
1100
1050
1500
1750
2000
2250
2500
2750
3000
3250
3500
3750
Distance from reference line [m]
Distance alongshore [m]
1500
1400
1300
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
b)
1976
1993
1997
Jetties/West
Bulwark
0
250
500
750
1000
1250
1500
1750
Distance alongshore [m]
Figure 7. Evolution of coastline in Kołobrzeg: (a) in 1931
(fotopolska.eu); (b) in October 2008 (Google Earth). Compare the beach
width 3 years after nourishment took place (in 2005) and immediately
after nourishment (2012) in Figure 2b.
The morphologic conditions along the shore of Kołobrzeg
vary greatly and sections of significant erosion, weak accretion
and a stable beach can be distinguished. The most obvious
changes are seen along the eastern coast, particularly at the
former Waldenfel`s Bulwark (now Kamienny Szaniec/East
Bulwark) at KM 331.5, except for the section located in the
shadow of the east jetty. Figure 8a illustrates the changes of
shoreline east of the port observed from 1965 to 1997, with
maximum retreat up to ca. 50 m within 32 years. Marcinkowski
and Ossowski (2008) provided erosion rates of 0.35 m/year on
average for a longer observation period between 1875 and 1979,
mentioning additionally a clear deepening of the shoreface
indicated by shifting of isobath -5.0 m towards the shore.
The mentioned steepening of the shoreface was amplified by
the construction of the seawalls, which allowed more energetic
waves to reach the shoreline and thus to generate rip currents
eroding the generally scarce dynamic sediment layer at the sea
bottom. This effect of the seawalls and the negative sediment
Figure 8. Measured shoreline position at Kołobrzeg: (a) at the east coast
in period 1965 - 1997; (b) at the west coast in period 1976 - 1997 (after
Szmytkiewicz et al., 1998).
A locally limited and rather weak sediment accumulation can
be observed at the east coast at the modern, 200 m long pier,
constructed in 1971 at KM 333.3. The area around the river
mouth shows also weak depositional processes of the sand
eroded on the eastern part of the coast as well as that of the
beach nourishment programme.
The shoreline west of the harbour is stable apart from the
section at D3 (see Figure 3a), as indicated by the shoreline
positions plotted in Figure 8b.
The coast is mainly eroded during the autumn and winter
storms. Water levels can increase, as a result of the associated
storm surges, by up to ca. 2.0 m (i.e. up to 3.0 - 3.5 m a.s.l.) as
indicated by the historical records in Table 1 (where water levels
higher than 550 cm result in a flood warning being given; higher
than 570 cm is a state of alert; over 600 cm correspond to storm
surges and higher than 650 cm to significant storm surges
according to Borodziuk, 2008). Typical storm conditions in
Kołobrzeg are shown in Figures 9a-c, during which the entire
beach is flooded and waves easily overtop the existing
waveblock units in the foreshore/seawalls. As a result, the sand
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Coastal Beach Stabilization at Kołobrzeg, Poland
137
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is washed away from the beach (see Figure 9d) – exemplarily,
the sand deposited in the 2005 nourishment process was
completely washed away already by November 2006 and further
60 % of the available sand were eroded by February 2007 as
analyzed by Łabuz (2012a). The beach did not recover due to
the lack of sediment supply. Apart from the degradation of the
natural environment, infrastructure losses are caused by heavy
storm surges - for example destruction of a part of a bike path to
the Podczele district in 2012 (Figure 9e) and washing out of the
wooden piles from the groynes built in the same year (Figure
9f).
Figure 9. Storm conditions and storm-induced damage on the east coast
of Kołobrzeg in 2012: (a) near entrance to the port; (b) overtopping of
waveblock units at Kamienny Szaniec (the East Bulwark); (c)
overtopping of sheet pile wall at Kamienny Szaniec; (d) eroded beach in
front of a sheet pile wall near the entrance to the port; (e) eroded bike
path; (f) washed out piles from the groynes built in 2012 (photos
courtesy of R. Dziemba, Miastokolobrzeg.pl).
The construction and successive expansions of the jetties in
the port in Kołobrzeg, located at the mouth of the Parsęta River,
has indisputably disturbed longshore sediment transport, as
reported by Szmytkiewicz et al., (1998). The first reference to
the port was made around 880 AD, although it was not until
1880 that it became an important German fishing port (City
Kołobrzeg). Nowadays, the port is used for trade, fishing,
passenger transport, naval and recreational activities.
Construction details for the port date back to the first half of the
19th century: structures stabilizing both banks at the river mouth
were modified in 1830 into crib-type jetties of length of 115 m
on the west and 155 m on the east side, and later, in 1853, into
mound-type jetties of length of 120 m and 200 m, respectively
(Marcinkowski and Ossowski, 2008). In order to achieve the
required water depth at the port entrance the jetties were
extended in 1858 to 214 m and 313 m, respectively. The current
geometry of the jetties is a result of the construction work that
took place in 2000 - 2010: the length of the east jetty was
extended to 452 m and that of the west one to 513 m (their
length yielded 205 m and 308 m before 2010, respectively). The
entrance to the port was widened from 40 to 80 m (Development
of Port of Kołobrzeg). Analysis of old maps indicated a retreat
of the shoreline after the construction of the port by 40 - 80 m at
the height of the East Bulwark and a simultaneous sand
accretion westwards of the port (Szmytkiewicz et al., 1998).
The construction and removal of marine fortifications from
the 19th century have also contributed to the changes in the local
shoreline. Kołobrzeg became an official fortification of
Brandenburg (Prussia) in 1653, however its defense role
increased after the war with France in 1807. Modification and
expansion works of the existing fortification facilities were
performed in 1832 - 1836, in the framework of which two
bulwarks were constructed at the shore: the Heyde`s Bulwark at
KM 334.6, protecting the port, and the Waldenfel`s Bulwark at
KM 331.5 with a rubble-mound embankment for the defense of
the east part of the fortification. The fortress-character of
Kołobrzeg hindered the parallel development of the health
resort, which led to the decommissioning of the land and marine
defenses in 1872 and 1887, respectively. The ruins of the
Waldenfel`s Bulwark were removed in 1972, resulting in very
intensive erosion of this coastal belt, stopped partially by the
construction of a sheet pile wall (see Figure 10a). The remains
of the Heyde`s Bulwark were removed during the reconstruction of the port in 2000 - 2010.
The tourist and recreational developments since the end of the
20th century have also caused negative impact on the coast. As
already mentioned, Kołobrzeg was already a famous sea resort
at the end of the 19th century and it has the potential to become
one of the most important tourist destinations in the western part
of the Polish Baltic Sea.
In order to increase its attractiveness, many hotels, restaurants
and apartments have been built on the seafront of the eastern
shore of Kołobrzeg, over the dune crests, while the western
coast remains relatively unaffected by human activity. Examples
of modifications to the coastal zone between KM 333.3 and KM
334.0 are shown in Figure 10b - the construction of a boardwalk
on the dune ridge as well as further adaptation of the region
behind the boardwalk resulted in a complete degradation of the
dune system.
COUNTERMEASURES AGAINST COASTAL EROSION:
A HISTORICAL OVERVIEW
The history of the protection measures taken against erosion
in Kołobrzeg is relatively long, reaching back to the second half
of the 19th century, when Kołobrzeg belonged to Prussia.
Nowadays, the existing coastal defense system, described in
Table 3 and shown in Figure 2a, is very complex and dense
(covering almost 80 % of the local shore according to Łabuz and
Łuczyńska, 2010), particularly on the ca. 3 km-long eastern part
of the shore. Prior to 2012 the protection measures against
flooding and erosion were ineffective, despite their number and
range (hard and soft - e.g., groynes, concrete seawalls, sheet pile
walls, waveblocks, tetrapods, dune reconstruction, beach
nourishment), as indicated by the shoreline changes in Figure 8.
A historical overview of shoreline protection at Kołobrzeg is
provided below.
Journal of Coastal Research, Special Issue No. 71, 2014
138
Strusińska-Correia
_________________________________________________________________________________________________
towards the open sea (Marcinkowski and Ossowski, 2008;
Łabuz, 2012b). During severe storm conditions, mentioned in
Table 1, the water level rises from the reference water level of
490 cm to more than 600 cm (i.e. 2.5 - 3.0 m above the reference
water level). As a result the seawall crown (located 3.0 - 3.5 m
above the reference water level) is overtopped by waves
reaching height of 1.0 - 2.0 m on average.
Table 3. Coastal defense structures at Kołobrzeg (based on Borodziuk,
2008; Marcinkowski and Ossowski, 2008).
No. Construction Beginning End
Length
year
(KM)
(KM)
(m)
PRUSSIA
1
1873
At 327.0 2
1887 – 1888 At 331.5 -
Figure 10. Examples of existing countermeasures against erosion at
Kołobrzeg: (a) a sheet pile wall with a reinforced cap west of the East
Bulwark; (b) tetrapods and waveblocks along the eroded dune at KM
330.89; (c) and (d) waveblocks used as a permeable breakwater at the
Eastern Bulwark; e) submerged breakwater with new groynes, f) beach
stabilization between KM 329.0 and KM 330.0; a combination of
geotextile sheets, rubble and fascines (photos (a) and (e) courtesy of A.
Głuszkiewicz, Moebius Bau Polska and B. Zabłocki, Port of Kołobrzeg;
photos (b) and (c) courtesy of M. Burdukiewicz, Urząd Morski Słupsk).
All photos taken between 2010 and 2012.
In the 19th and at the beginning of the 20th century, wooden
groynes were the most common structures used for beach
stabilization. Already in 1873, the east part of the shore at KM
327.0 was protected by 13 groynes and another 7 groynes,
together with fascine mattresses, were constructed in 1887 1888 at the East Bulwark at KM 331.5 (Marcinkowski and
Ossowski, 2008). In 1898 construction of a wooden seawall
between KM 331.56 and KM 333.31 and of another 13 groynes
began. Five years later the protection system was extended by
new groynes of length of 90 - 100 m and spacing of 100 - 200 m
between KM 324.0 and KM 332.88, which was further
expanded in the 1930`s (see Table 3).
In the period 1955 - 1957 a two-row seawall made of wooden
piles, filled with concrete blocks, was built between KM 330.08
- KM 330.94 and KM 334.72 - KM 336.92. But it was not until
the 1960`s, when the country became stable after the World War
II, that important countermeasures against erosion at Kołobrzeg
were re-started by the Polish authorities (see Table 3).
Due to the poor condition of the existing groynes, resulting from
the lack of maintenance, a new protection method was
introduced at the end of 1980`s, namely seawalls made of sheet
pile walls with a reinforced cap, shown in Figure 10a. In fact,
the seawalls caused even more intensive erosion of the coast
instead of protecting it against negative wave impact, as they
have modified the local hydrodynamics by introducing highly
reflective conditions, responsible for washing the sediment away
3
1898 – 1901
4
1906
30`s
Structure
type
13 wooden groynes
Fascine mattresses
7 new wooden
groynes
331.56
333.31 1750
Wooden seawall
13 new wooden
groynes
Ca. 324.88 332.88 Ca. 8000 Wooden groynes
(length 90 - 100 m
spacing 100 - 120 m)
Expansion of the
groyne group
POLAND
5
1982,
1984 – 86
331.40
331.71
315
6
7
1984 – 86
1990
331.70
333.69
332.55
333.89
850
200
8
1992
330.58
330.88
300
9
1993
333.57
353.89
320
10
1993 – 94
333.46
333.57
110
11
12
1994
1995-96
330.58
330.28
330.89
330.57
310
292
13
1994 – 95
330.89
331.37
485
14
1994 – 95
1997 – 98
331.55
331.71
331.70 150
332.11 400
15
2002 – 03
332.055
332.52 465
16
-
331.35
331.67 320
17
-
334.50
334.72 220
18
2010 – 2012
330.40
333.40 3000
Sheet pile wall
with a reinforced cap
Sheet pile wall
Slope stabilization
using geotextiles
Sheet pile wall
with a reinforced cap
Sheet pile wall
with a reinforced cap
Sheet pile wall
with a reinforced cap,
geotextiles filled with
sand at seaward toe of
the seawall
Tetrapods at wall 12
Sheet pile wall with a
reinforced cap,
tetrapods at the wall
Waveblocks along
shoreline
Waveblocks in the sea
Reinforced cap built
on sheet pile wall 6
Reinforced cap built
on sheet pile wall 6
Rubble mound
embankment
Rubble mound
embankment
Submerged
breakwater, groynes
Since the beginning of the 1980`s, the beach east of the port,
mostly between KM 330.5 and KM 331.8, has been nourished to
counteract the erosion that causes a steady narrowing of this
Journal of Coastal Research, Special Issue No. 71, 2014
Coastal Beach Stabilization at Kołobrzeg, Poland
139
_________________________________________________________________________________________________
stabilization of the eastern part of the coast. The latter is worth
of a discussion, since it was originally invented to stabilize
banks on Lake Huron in Canada (CANLAND, 1995). A single
unit, shown in Figure 14, is 3.0 m long and 1.6 m wide, weighs
6 t and can be combined in a line-type of protection.
Nourishment
section of the shore. After a 10 year break between the first and
second nourishments, the works were repeated almost every
year till 2005 with the volume of the nourished sand rarely
exceeding 100,000 m3, as shown in Figure 11 (Marcinkowski
and Ossowski, 2008). The effect of the nourishment was not
permanent, since the artificially widened beach regressed to the
pre-nourishment state in the first storm season, as the sand was
easily washed away, as illustrated in Figures 12 and 13. The last
nourishment was performed in 2012, after the construction of
the submerged breakwater, with 702,873 m3 of sand deposited
between KM 330.4 and KM 333.4 in order to widen the beach
by more than 40 m.
Sediment [%] related to
nourished sand volume in 2005
Linear changes of sediment
800000
Figure 13. Changes of the nourished sand volume from 2005 to 2010
for a cross section at KM 331.5 (after Łabuz, 2012b).
600000
KM 331.27 - 331.67
90000 m³
KM 333.5 - 334.0
81600 m³
KM 330.4 - 330.9
65400 m³
KM 330.535 - 331.335
120000 m³
KM no data
80000 m³
KM no data
10000 m³
KM no data
12000 m³
KM 331.295 - 331.827
161200 m³
1982
1992
1994
1995
1996
1998
2000
2003
2004
2005
400000
300000
200000
KM 330.4 - 333.4
700000 m³
KM 330.5 - 331.0
110000 m³
500000
KM 331.3 - 331.6
41500 m³
Sediment volume used [m³]
700000
100000
0
2012
2025
Year [-]
Figure 11. Beach nourishment at Kołobrzeg since 1982.
Figure 14. Construction details of a single waveblock unit: (a)
dimensions; (b) 3D-view; (c) pre-fabricated unit (photos courtesy of M.
Burdukiewicz, Urząd Morski Słupsk).
Figure 12. Conditions on the eastern part of the beach in Kołobrzeg: (a)
and (b) before nourishment in 2012 at the East Bulwark and west of the
East Bulwark, respectively; (c) and (d) after nourishment in 2012 at the
East Bulwark (photos courtesy of A. Głuszkiewicz, Moebius Bau Polska
and B. Zabłocki, Port of Kołobrzeg).
Later in the 1990`s other protection methods such as tetrapods
(see Figure 10b), geotextiles and waveblocks were used for the
All the elements (i.e. three platforms at an angle of 11°,
connected by vertical columns of varying number in a staggered
arrangement) are made of reinforced concrete. The particular
geometry of this structure enables dissipation of the energy of
incoming waves, reduction of wave reflection as compared to
seawalls as well as more efficient deposition of the sediment at
the landward side of the unit. Two types of protection were
constructed in Kołobrzeg in 1994 - 95 using the waveblock
units: (i) a 485 m-long stabilization of the eroded dune between
KM 330.896 and KM 331.379, as shown in Figure 10b; (ii) a
150 m-long barrier placed on the foreshore between KM
331.555 and KM 331.705, closed at both ends with groynes
made of tetrapods as shown in Figures 10c and d. The latter acts
as a permeable breakwater, protruding by 0.46 m above the
reference water level of 490 cm, while during storm surges it
becomes a completely submerged structure with a reduced
capability of wave attenuation. Exemplarily, the waveblocks
were completely submerged during the storms on 1.11.2006 and
18.1.2007 that caused water level increase up to 660 cm and 640
cm, respectively. According to the field measurements
performed by Łabuz and Łuczyńska (2010) from January 2006
Journal of Coastal Research, Special Issue No. 71, 2014
140
Strusińska-Correia
_________________________________________________________________________________________________
to March 2008, a 250 m wide section of the coast behind the
waveblock barrier was continuously eroded. As shown in Figure
15, the width of the beach decreased from ca. 27 m to 0.0 m and
its height at the toe of the seawall was reduced from 1.7 m above
the reference water level to -0.3 m below it. As observed by
Łabuz and Łuczyńska (2010), the original position of the
waveblocks placed on the dune and in the sea has been changed
by successive storms. According to measurements taken in
2010, the waveblocks at the dune subsided by up to 0.26 m as
the sediment beneath was washed away and the block inclined
towards the sea by 25°. The position of the waveblocks placed
in the sea was modified more as a result of scouring – in the
profile considered, they subsided by 0.32 - 0.38 m, and were
moved towards the shore by 0.10 - 0.15 m and inclined in the
same direction. These changes to the original geometry can be
easily observed in Figure 10d, taken in 2012.
The recent, most spectacular Polish investment in the field of
coastal engineering is the construction of a 3 km-long
submerged breakwater, between 2010 and 2012, to stabilize the
eastern part of the coast from KM 330.4 to KM 333.4. The
breakwater is a continuous permeable structure of a rubble
mound type, consisting of 12 main segments (of 95.7 - 240 m in
length and a freeboard of 0.7 m) connected with lower units (of
length of 32 - 40 m and a freeboard of 1.1 m). The structure is of
trapezoidal cross-section, with seaward and landward slopes of
1:4 and 1:2, respectively. The width of the crown is of 0.6 m,
while the base width varies from 15 to 20 m, depending on local
water depth (Borodziuk, 2008). The breakwater was constructed
at a distance of 120 - 150 m from the shoreline, at a water depth
of 2 to 4 m. The base of the breakwater was made of a 0.3 m
thick granite rubble layer with block weight of 0.5 - 4 kN,
placed on a geotextile sheet, while the breakwater body was
made of heavier granite blocks of weight of 6 - 8 kN.
4
SSE
Sand
dune
3
Elevation [m]
NNW
Sheet
pile
wall
2
Nourishment
09.2005
Waveblock
movement
Till
1
07.01.2006
28.11.2006
08.02.2007
07.05.2007
28.03.2008
15.04.2010
23.10.2010
Gravel/pebble
0
-1
-2
0
10
20
30
50
40
60
70
Sand
Distance [m]
Figure 15. Beach erosion in front of waveblock barrier and waveblock
unit relocation observed at cross section at KM 331.5 (after Łabuz,
2013).
In order to prevent longshore sediment transport, both ends of
the structure were closed with groynes and an additional 35
wooden groynes (110 m long, with a pile diameter of 0.3 - 0.42
m and a spacing of 60 - 106 m) were constructed along the
breakwater as presented in Figure 10e. After the construction of
the breakwater, the beach was nourished, using more than
700,000 m3 of sand (see Figures 11, 16c and d). The investment
cost more than 62 million Polish zloty and was first of this type
used in Poland to protect the coast from erosion.
DISCUSSION
Coastal erosion around Kołobrzeg, more intensive than in
adjacent regions, is conditioned predominantly by the
unfavourable local morphology, which results in more energetic
wave conditions, particularly east of the Parsęta River.
Additionally, even during moderate storms, the low-lying beach
is easily flooded and prone to wave impact. The beach cannot
recover naturally due to the constant negative sediment budget
and the general lack of local sources of fine sediment, since (i)
the substratum is composed of till, (ii) the only available, thin
sediment layer is mainly coarse sediment such as gravel,
pebbles, coarse sand, (iii) the influx of the sediment from
adjacent coastal sections is blocked by the existing protective
structures and the jetty at the port entrance. Other problems are
the constant degradation of the eroded dunes by tourists and the
increase in tourist infrastructure, built over the dune ridges and
in the hinterland. The existing coastal defense system, in
particular the seawalls, and the lack of fine sediment hamper
natural dune regeneration. As reported by Łabuz and Łuczyńska
(2010), the dunes have been planted using selected vegetation
species in order to improve their stabilization but this is
insufficient when the number of visitors, often with poor
ecological awareness, continues to rise.
In the case of the wooden groynes, the long period between
World War I and the reconstruction of Poland, when there was
no maintenance of these structures, caused significant damage to
the piles; many of them were simply washed away by wave
action and not replaced. The incomplete structure of the groynes
and the generally poor condition of the wooden piles has
lowered their effectiveness. The erosive processes were
intensified by the subsequent construction of the vertical
seawalls. Due to the highly reflective character of these
structures, the sea bottom in front of the seawalls has been badly
eroded, exposing gravel and pebble accumulations in the
substratum. Moreover, the height of the seawalls is insufficient
to prevent wave overtopping during severe storms, as it was
observed during the past storm events. The application of
tetrapods and rubble to stabilize the slopes/toes of the eroded
dunes was also unsuccessful as the elements sank into the sand.
Regarding the waveblock barrier built on the foreshore, this
has had a very negative impact on the environment. Firstly, the
barrier can effectively attenuate the incoming waves solely in
normal sea conditions, while during storms it is easily
overtopped. Secondly, longshore sediment transport was
disturbed by creating what is, in effect, a closed box, which also
precludes the influx of the sediment previously washed away
from the beach and its re-deposition on the landward side of the
barrier. In addition, the construction became unstable due to
scouring at its base, and as a result many units subsided and
inclined. Moreover, the waveblocks hampered the natural water
exchange and, like the seawalls made of tetrapods, significantly
impaired the natural beauty of the beach and worsened bathing
conditions (see Figures 16a - c).
Considering the need to retain the “natural”, attractiveness of
the coast for tourism, an “invisible” submerged breakwater is the
most preferable “hard solution” for the purposes of beach
Journal of Coastal Research, Special Issue No. 71, 2014
Coastal Beach Stabilization at Kołobrzeg, Poland
141
_________________________________________________________________________________________________
stabilization. However, the breakwater built at Kołobrzeg is a
very long, continuous structure (ca. 3 km long) with a freeboard
which might not be sufficient to force the waves to break over
the crest during storm surges of over 2 m. This situation will
again induce erosion of the beach, since the waves reaching the
shore will be sufficiently energetic to wash the sand away, over
the breakwater, towards the open sea (Łabuz, 2012b). Although
permeable, it is also expected to negatively influence the water
exchange between the offshore and foreshore. Further, by
closing the ends of the breakwater and the construction of the
very dense group of groynes, modifications to the longshore
sediment transport and water circulation were introduced. The
geometry of this structure, expected to be more effective in
preventing washing away of sand as compared to a system of
detached breakwaters, was dictated by the critical state of this
beach.
Figure 16. Impact of the structural measures taken against erosion in
Kołobrzeg on natural and tourist values of the local environment: (a), (b)
and (c) eastern coast at the East Bulwark (Kamienny Szaniec), west
from and east from the Bulwark, respectively, before 2012; (d) after the
construction of a submerged breakwater and beach nourishment in 2012,
east from the jetties (photo (a) courtesy of A. Szumski,
http://www.wybrzeze.com.pl; photos (b) and (c) courtesy of M.
Burdukiewicz, Urząd Morski Słupsk; photo (d) courtesy of A.
Głuszkiewicz, Moebius Bau Polska and B. Zabłocki, Port of Kołobrzeg).
The most environmentally and tourist-friendly alternative is
beach nourishment, as shown in Figure 16d. However, due to
the necessity for a systematic repetition of nourishment in order
to maintain the required beach width, this solution is regarded as
ineffective and temporary by public opinion. Thus, the
application of “hard solutions” is generally preferable as their
performance is believed to be long-term. Finally, as discussed
by Marcinkowski and Ossowski (2008) and Łabuz (2013), the
volume of sand used for beach nourishment at Kołobrzeg was
very often insufficient when compared to that washed away
during storms (typically 70 m3/m). It is also the case of the latest
nourishment in Kołobrzeg in 2012.
CONCLUSIONS
The coastal defense structures at Kołobrzeg were not always
designed to meet the criteria of the lowest impact on the natural
ecosystem/tourism, but rather according to the principle “the
more, the better”. Considering the high number and the diversity
of the structures used, one has an impression that the coast of
Kołobrzeg, particularly the eastern part, has been used to test
their effectiveness in reducing erosion without any preunderstanding of their impact on the adjacent coastal sections
and the environment. It is highly recommended to use soft
methods of beach stabilization such as nourishment (under
condition of a correct determination of the volume of the
required sand) and in critical cases, to combine them with
carefully designed structures, such as detached breakwaters.
ACKNOWLEDGMENTS
This publication is one of the results of the Regional Network
Latin America of the global collaborative project ‘‘EXCEED –
Excellence Center for Development Cooperation – Sustainable
Water Management in Developing Countries’’ which consists of
35 universities and research centres from 18 countries on 4
continents. The author acknowledges the support of the German
Academic Exchange Service DAAD and the Centro de
Tecnologia e Geociências da Universidade Federal de
Pernambuco,the Fundação de Amparo a Ciência e Tecnologia
do Estado de Pernambuco-FACEPE and the Instituto de
Ingeniería of the Universidad Nacional Autónoma de México for
the participation in this EXCEED project.
The author would like to express gratitude to Mr. B. Zabłocki
and Mr. A. Głuszkiewicz for providing the technical data and
photos of the submerged breakwater as well as to Prof. K.
Furmańczyk, Dr. T. Marcinkowski and Dr. T.A. Łabuz for the
permission to use their data, sharing literature related to the
coastal erosion in Kołobrzeg and discussion. Special thanks to
Dr. M. Burdukiewicz for the waveblock technical data sheet and
the photos as well as to Mrs. D. Ścisła-Trojanowska for the
information about the geometry of Port of Kołobrzeg. The
author would also like to acknowledge Mr. T. Łowkiewicz
(http://twierdzakolobrzeg.pl/), Mr. J. Guzdek, Mr. R. Dziemba
(Miastokolobrzeg.pl)
and
Mr.
A.
Szumski
(http://www.wybrzeze.com.pl/) for the permission to use their
photos.
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