Christian Helledie
Beach Nourishment at the Inner Danish Waters
Christian Helledie, COWI, Parallelvej 2, 2800 Lyngby, Denmark, [email protected]
Introduction
The coasts at the inner Danish waters have been developed over the last century with summer
houses and towns, as early planning regulation allowed development close to the sea. The
coast is naturally eroding many places, which has led to an increasing demand for coastal
protection of private property. The first coastal protection schemes were often uncoordinated
and focused on structures such as groynes and revetments, which to a large extent fixed the
coastline. Today many beaches at the inner Danish waters are dominated by un-aesthetic and
ineffective old shore protection structures. The widespread stabilization of the coast by
revetments has reduced natural supply of sand to the beaches and thus extensive beach
recession has followed. The eroding beaches provide less protection of the hinterland and
access along the coast is often difficult, which reduces the recreational value.
COWI has undertaken a series of successful shore rehabilitation projects at the inner Danish
waters focusing on beach nourishment and aiming at providing aesthetic solutions with high
recreational value and effective protection, see Figure 1. The paper outlines background,
objective, financing and technical performance of the projects.
Gribskov Municipality
Elsinore
Municipality
Liseleje
Halsnaes
Municipality
Funen
Zealand
Figure 1 Beach nourishment projects at the inner Danish waters designed by COWI
Beach Nourishment at Funen (1997-2011)
The Site
The site at Funen is situated at the north coast where 2500 summer houses and farms are
found along the 12 km low-lying coast, see Figure 2. The coastline is convex and the
longshore net sediment transport increases from approx. 8,000m3/year at Egebjerggaard to
approx. 20,000m3/year at Kristiansminde and approx. 26,000m3/year at Erikshaab resulting in
a deficit in the littoral budget estimated to 18,000m3/year. The increasing longshore sediment
transport towards east is assessed to be the main reason for the historic beach recession found
along the western part of the coast. The erosion problem was smaller east of Kristiansminde
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Christian Helledie
due to the input of sand from
west and more efficient
groynes.
Generally,
the
hinterland is protected from
flooding by levees and
revetments and the beach is
protected from erosion by an
old groyne field. The groynes
were built with an average
spacing of 75m and extend
30m out from the revetments.
At some exposed locations
breakwaters
have
been
constructed between
the
groynes. The ineffective and
old shore protection structures
could not prevent beach
recession and storm damage
on levees and private plots
and the recreational value of
the beach was reduced.
Figure 2 Site at the north coast of Funen
Project Objective
In 1998 the local coastal protection association (Det nordfynske kystsikrings-, dige og
pumpelag) commissioned COWI to analyse the existing situation and on this basis develop a
long term shoreline management plan for the coast. The objective of the project was to reestablish attractive sandy beaches and increase shore and flood protection to reduce risk of
damage to private property and at the same time improve the recreational value of the coast.
Beach nourishment was found to be the most feasible and attractive solution considering the
available funding. Beach nourishment is the only measure which can re-establish sandy
beaches and help mitigating deficits in the sediment budget and hereby eliminate shoreline
recession. Due to limited funding, it was decided not to focus on hard coastal protection
structures as they would not re-establish sandy beaches. The existing shore protection
structures were generally preserved. Levees and revetments were strengthened at selected
locations to increase flood protection. The new beaches are designed to be mobile, but new
beach breakwaters have been introduced at a few exposed headlands to stabilise the beach.
The beaches are re-nourished at 4 years interval to maintain sufficient beach width and
minimise unit cost of sand. The maintenance nourishment is designed to compensate the
deficit in the littoral budget estimated to 18,000m3/year. Due to eastward littoral net drift
maintenance nourishments are made along the western beaches. The sand is dispersed along
the coast by the littoral drift, thus securing long term input of sand at the eastern beaches.
Financing
The beach nourishment scheme is financed and maintained by the local coastal protection
association. The members are private summer house owners and farmers possessing land
along the low-lying coast and at the hinterland. Due to severe flooding risk the landowners
have had a tradition for working together fighting flooding hazards.
The Municipality is not playing an active role in maintaining the beach scheme, but handles
the collection of contributions from the plot owners, which is paid as a separate real estate tax.
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Christian Helledie
Figure 3 and Table 1 show the cost of development and maintenance of coastal protection
over the years and the dominant measures implemented. The data has kindly been provided by
Mogens Stougaard from the coastal protection association.
The total cost of development and maintenance of coastal and flood protection along the
11.4km coast is estimated to DKK 39 million between 1995 and 2009. The yearly average
cost is estimated to DKK 2.6 million, corresponding to DKK 230,000 year/km coastline. The
total number of plot owners is around 2500 each paying DKK 1500 year, which is in line with
the yearly cost of maintaining the coastal protection scheme when seen over the years.
The maintenance cost varies significantly from year to year. The initial beach nourishment
was made in 1999 including
113,000m3 sand and followed up
in 2001 with 70,000m3 to reestablish the sandy beaches.
Hereafter, the cost of the
maintenance nourishments is
relatively
constant
including
70,000m3 every 4 years. At the
east side of some headlands, the
applied quantities of beach
nourishment have not been
sufficient to maintain acceptable
beach width. Therefore 11
breakwaters were built in 2004 and Figure 3 Cost of development and maintenance of
another 4 in 2009, see Figure 2.
coastal protection between 1995-2009
Table 1 Total cost of development and maintenance of coastal protection 1995-2009
Measures
Cost DKK ex. VAT
Beach
nourishment
Beach
breakwaters
Revetments
Design and
studies
11,300,000
1,900,000
24,800,000
1,100,000
Total
39,200,000
In November 2006 the coast was hit by a severe storm with storm surge of up to +1.74m
MSL, which is assessed to be a 50 year Return Period event. The storm caused extensive
damage to the revetments along the coast. The damages were repaired in 2007, 2008 and 2009
where 90% of the revetments were rebuilt, which increased maintenance cost significantly.
Table 1 shows that the cost of beach nourishment is around half of what has been spent on
revetments.
Technical Performance
The shoreline management plan developed by COWI has principally been implemented.
However, locations of maintenance nourishment and new breakwaters have been adjusted to
optimise the scheme. The extensive rebuilding of revetments was not part of the initial
shoreline management plan, but the consequence of the impact of the 50 year Return Period
storm in 2006.
The implemented beach nourishment scheme has re-established attractive sandy beaches
along the entire coast increasing both recreational value of the beaches and protection of the
hinterland, see Figure 4. Figure 5 shows that the beach at the western part of the coast was
eroding between 1954 and 1999 due to the convex coastline and the littoral net drift towards
east. The beaches towards east were almost stable between 1954 and 1999 due to the more
effective groyne field here and the input of sand from the eroding beaches towards west. In
1999 the initial nourishment was made at the western beaches, which significantly increased
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Christian Helledie
the average beach width. The severe storm in 2006 caused beach recession along the coast,
which can be seen in 2008. However, recently the beach is recovering from the storm as the
sand migrates back towards the shore. Additionally, three sections at the western part of the
coast were re-nourished in 2009, see Figure 2.
The nourishment has stopped beach recession at the western part of the coast (Groyne 28112). Positive signs of the beach nourishment can also been found at the eastern part even
though nourishments have not been undertaken here (Groyne 112-176).
Groyne 57 Before nourishment 1999 and 2010
Groyne 72 Before nourishment and breakwaters 1999 and 2010
Figure 4 Effect of beach nourishment and coastal protection 1999-2010
Beach nourishment is dynamic and
the sand slowly migrates from west
towards east thus benefiting the
entire coast in the long term.
Therefore, beach nourishment can
be financed by a large group of land
owners along the coast similar to
flood protection.
The beach nourishment at Funen
must be maintained at intervals to
Figure 5 Historic development of beach width
balance the deficit in the littoral
budget and avoid beach recession.
The old groynes have a stabilising effect on the beach as the orientation of the shoreline
between the structures generally is oblique. However, the old groyne field is not sufficient to
stabilise the beach everywhere. The implemented scheme has not included rehabilitation of
the old groyne field. A large part of the shore protection structures are not functioning optimal
and reduce the recreational and aesthetic value of the beach. The new breakwaters help
stabilising the beach at exposed locations where the old groynes were not sufficient. Beach
nourishment is not a stand alone shore protection measure at Funen. Revetments are needed to
protect the hinterland against storm impact when houses are located close to the sea.
Rehabilitation of Coastal Protection at Liseleje (1996-2005)
The Site
Liseleje is located at the NW side of Zealand at a long straight coast including a small
headland at Hyllingebjerg. The site covers a 2.7km coastline, where high till cliffs have been
eroding in the past, see Figure 6. The old Liseleje Breakwater is located at the east end of the
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Christian Helledie
site, which has served to protect boats of the local fishing community over the past century.
Towards east a marine foreland is found with dunes and sandy beaches.
Liseleje
Breakwater
Bay 3
North
4
5
6
7
8
Hyllingebjerg
Liseleje
Figure 6 Historic development of the beach at Liseleje
The yearly net littoral drift is estimated to 10,000-30,000m3/year towards NE.
The hinterland at the eroding cliffs has been developed with a large population of summer
houses. Cliff erosion has been an increasing problem threatening some villas along the cliff
top and the private plot owners independently tried various methods to stabilise the cliffs. As
a consequence, the coast in 1996 was dominated by un-aesthetic, un-coordinated and
ineffective old coastal protection structures and the beach had disappeared due to erosion,
thus reducing the recreational value of the coast, see Figure 6.
Project Objective
In 1996 COWI was commissioned by Frederiksborg County to develop a shoreline
management plan for the 2.7km coastline south of the Liseleje Breakwater, see Figure 6. The
project was made in corporation with Frederiksvaerk Municipality and the 90 summer house
owners along the cliff, who had formed a coastal protection association.
The objective of the project was to provide protection of private property along the cliffs. The
shoreline management plan should focus on increasing the width of the beach and access
should be provided along the coast. Additionally, the maintenance requirements of the scheme
should be minimised.
The shoreline management plan developed by COWI included removal of all existing
ineffective shore and coastal protection structures except the Liseleje Breakwater and the two
breakwaters towards south. Seven new large, low crested beach breakwaters were constructed
at 1.5m water depth to protect the new beaches. The number of breakwaters were minimised
to reduce visual impact of the scheme and construction cost. The scheme also included
rehabilitation of the revetments along the cliffs. Finally, the sandy beaches were reestablished by beach nourishment with a total of 70,000m3 sand. The shoreline management
plan recommended maintenance nourishment at 5-10 years interval.
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Christian Helledie
Financing
The shoreline management plan and the rehabilitation of the shore protection scheme between
Hyllingebjerg and Liseleje were financed by Frederiksborg County, Halsnaes Municipality
and the private plot owners along the cliff, see Table 2. The new beaches and breakwaters
protect the cliffs, but also increase the recreational value of the coast and were therefore partly
financed by public funding. The revetments are for stabilising the cliffs only and were
therefore financed by the private plot owners along the cliff.
Table 2 Cost of development and maintenance of shore protection at Liseleje
1999-2010. Frits Thaulow, Head of the coastal protection association
Nourishment and breakwaters
DKK ex. VAT
Revetments
DKK ex. VAT
Approx. total cost
DKK ex. VAT
Initial scheme 1999
~8,800,000
~2,400,000
~11,200,000
Additional breakwater
~1,600,000
Measures
Additional revetments
Misc. maintenance
Financing
~1,600,000
~1,200,000
~1,600,000
33% Coastal Funding, DCA
33% Municipality
33% Plot owners 1. row
~1,200,000
~1,600,000
Plot owners 1. row
~15,600,000
The total construction cost of the shore rehabilitation scheme was approx. DKK 11.2 million
in 1999 corresponding to DKK 4.1 million per km coastline.
The local coastal protection association is undertaking the maintenance of the scheme at
Liseleje, but the Municipality is playing an active role. The total maintenance budget is DKK
420,000 per year split equally between the municipality, the 90 plot owners along the Cliffs
and the Coastal Funding administrated by the Danish Coastal Authority, DCA. The
contribution of the private plot owners is determined according to the length of the cliff side
of the plots equal to DKK 51 per meter, which on average is DKK 1,500 year/plot.
The coastal protection association now focuses on optimising the breakwaters to reduce
maintenance cost in the future. Generally, the maintenance budget has been spent on a new
breakwater and small adjustments of others. Beach scrapes have been undertaken moving
sand from large tombolos to starving sections to optimise the scheme. The yearly maintenance
budget is DKK 150,000 km/year, which has been insufficient to maintain the scheme.
In 2005 two additional breakwaters and beach nourishment were constructed north of the
Liseleje Breakwater at the popular public beach, which was suffering from leeside erosion.
The additional breakwaters were financed by the municipality as they are outside the area
administrated by the local coastal protection association.
Technical Performance
The implemented scheme developed by COWI was made with a minimum of breakwaters to
reduce visual impact and construction cost. Generally, the pocket beaches between the large
breakwaters and the tombolos are relatively stable, which minimises the maintenance
requirements. Most of the pocket beaches appear natural and aesthetically attractive with wide
sandy beaches as the number of structures is small, see Figure 7.
However, the beaches at Bay 2, 3 and 4 have been eroding and after some years disappeared
at the centre of the bays, see Figure 7. Bay 5, 6, 7 and 8 on the other hand have collected
more sand over the years, which have increased the width of the beach more than 10 years
after the initial nourishment. Dunes have formed at the wide tombolos, which show the
efficiency and success of the applied shore protection scheme. From having suffered from
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poor recreational value this coast now has some of the most attractive recreational sandy
beaches at the north coast of Zealand and the cliff recession has stopped.
Narrow beach at Bay 4 and wide attractive beach and new dunes at Bay 6
Figure 7 Beach and coastal protection at Liseleje, 2010
Large scale maintenance nourishment with imported sand has not been undertaken as initially
recommended by COWI. Maintenance nourishment is assessed to be expensive in the long
run due to relatively high mobilisation cost of a dredger.
The coastal protection association has chosen to focus on optimisation of the breakwater
scheme to preserve the beaches and hereby reduce future loss of sand. However, the effect of
the beach scrapes and additional breakwater has not been sufficient to preserve the beaches at
the critical sections. Therefore, additional optimisation of the breakwaters is planned.
The shore protection scheme at Liseleje shows that it is possible to re-establish the sandy
beaches at the inner Danish waters and to a large extent stabilise the new beaches by use of
large beach breakwater even at locations with significant deficit in the littoral budget. It
should be stressed that in most cases maintenance nourishment is required even with an
efficient breakwater scheme to compensate loss of sand and avoid lee side erosion.
Additionally, revetments are required to stabilise the high cliffs against storm erosion.
Large breakwaters are known to form rip currents during periods with rough sea, which has
also been observed at Liseleje. Beach users should be made aware of this potential hazard
during rough conditions.
Feasibility Study for Beach Nourishment at Zealand (2009-2011)
The Site
The 30km coast in Gribskov
Municipality is convex with a series
of headlands and bays, see Figure
8. Generally, the headlands are till
cliffs. Marine forelands with sand
and shingle beaches are found in the
bays between. The coast and
hinterland is dominated by areas
with summerhouses, many places
extending to the cliff edge or beach.
The littoral net drift is towards NE Figure 8 Coast in Gribskov Municipality and
and E and increases from Tisvilde nourishment scheme proposed by COWI
towards Gilleleje and then declines
east of the harbour. The deficit in the littoral budget is estimated to 40,000-50,000m3/year
between Tisvilde and Gilbjerg Hoved. East of the harbour the deficit is assessed to 15,00025,000m3/year, as Gilleleje Harbour blocks most of the littoral drift and sand dredged from
the access channel is currently dumped in deep water.
Figure 9 shows the assessment of the historic shoreline recession along the coast in Gribskov
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Christian Helledie
Municipality. Generally, the
beaches have receded 10-30m
between 1954 and 2009 except
at some headlands providing
local hard points. The figure
also shows that the beaches
have accumulated at the west
side of Gilleleje Harbour and at
Dronningmoelle where the
shoreline is concave, thus
reducing the littoral drift.
The natural supply of sand
Figure 9 Shoreline recession in Gribskov Municipality
from the cliffs at the NW coast
of Zealand has been reduced over the years due to cliff protection by revetments, see Figure
10. Therefore, the sandy beaches have generally receded and disappeared at several locations.
The existing protection structures have often been constructed by private plot owners and
small coastal protection associations for small sections of coastline. The coastal protection is
generally uncoordinated and based on poor design and the structures are of low quality.
Furthermore, the structures have generally not been maintained sufficiently probably due to
limited funding and lag of coordination. The focus of the plot owners along the cliffs often is
to protect the high value properties against erosion typically applying revetments, see Figure
10. The beaches and shore protection structures are secondary. The result is narrow eroding
beaches and limited access along the coast thus reducing the recreational value of the coast.
Narrow beach in front of revetments furthermore reduces protection of the hinterland and
increases risk of storm damage to the properties along the cliffs.
Old coastal protection and narrow beach at Tisvilde and large new revetment at Trillingerne
Figure 10 Existing conditions along the coast in Gribskov Municipality, 2009
Project Objective
Gribskov Municipality has commissioned COWI to prepare a feasibility study for a regionally
coordinated beach nourishment scheme for the 30km coastline in Gribskov Municipality. The
purpose of the feasibility study is to provide a technical foundation for the political decision
process for the nourishment project.
The project has been initiated by private stakeholders headed by Jackob Wandall and Birgit
Lund. The initiators, the municipality and other stakeholders have formed a working group
with the objective to develop the beach nourishment project and secure regional coordination
of interests. The municipality has provided technical and administrative support for the
project with Hanne Askholm Larsen as primary contact and political leadership from Mayor
Jan Ferdinansen. Ole Juul Jensen and Christian Helledie from COWI and Per Soerensen from
DCA have provided technical expertise.
The objective of the nourishment scheme is defined by the working group. The project shall
re-establish sandy beaches in Gribskov Municipality and hereby increase protection of the
coast and recreational value of the beaches. The beach nourishment should benefit as many
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Christian Helledie
citizens as possible and therefore be regionally coordinated within Gribskov Municipality.
Ideally, the project should also include the neighbour municipalities Halsnaes and Elsinore,
who is part of the regional sediment cell at the north coast of Zealand, see Figure 1.
Unfortunately, the adjacent municipalities have not found sufficient political support to join
the nourishment project at present.
The selected beach nourishment scheme in Gribskov Municipality is seen as a supplement to
the existing coastal protection structures that is excluded from the nourishment project. The
existing coastal protection structures have been developed and are maintained by private plot
owners along the cliffs and primarily focus on protection of the cliffs. However, to obtain the
best possible effect of the planned nourishment scheme the local coastal protection
associations should clean up their part of the beach and ideally optimise their shore protection
structures before the beaches are nourished.
Financing
The selected nourishment scheme is presented in Figure 8. The scheme provides a 25m
increase in beach width at selected locations, which are concentrated at the SW part of the
coast as the need for nourishment is large here. This will also secure the longest possible
effect of the nourishments within the municipality, as the littoral net drift disperses the sand
towards NE. To obtain an immediate effect along the entire coast suitable sections have also
been selected for nourishment along the N and E part of the coast.
The initial beach nourishment is assessed to 625,000m3 and the total cost is estimated to DKK
37 million or DKK 1.2 million per km coast. The cost of the initial nourishment is proposed
to be split over 3 years to reduce the yearly cost and to optimise the initial nourishment.
The maintenance strategy is to replace the estimated deficit in the littoral budget by beach
nourishment at 3 years interval. Hereby, the unit cost of sand can be reduced. The yearly
maintenance cost is estimated to DKK 3.2 million or DKK 100,000 km/year. Additionally,
sand dredged from the access channel to Gilleleje Harbour is to be placed at the beach east of
the harbour on a yearly basis to mitigate part of the deficit in the littoral budget. This is a
change in port operation and thus not a part of the nourishment project.
The proposed strategy for the beach nourishment scheme implies that the project can be
financed by a large group of citizens, as the project both aims at increasing coastal protection
and improves the recreational value of the coast.
A new financing model has been developed by the private landowners headed by Jakob
Wandall, see Table 5. The beach nourishment scheme is proposed to be financed by all land
owners within a 1km wide zone along the coast through an excise duty. To be consistent with
Danish regulations the contribution shall be determined for individual land owners based on
utility value here defined as the distance to the beach. The model has been approved by
Gribskov Municipality.
The public opinion towards the Table 3 Financing model for beach
proposed nourishment scheme has been nourishment DKK ex. VAT
positive based on experiences from
Initail nourishment cost / year / plot owner Plot owners DKK excl. VAT
0-200m
2834
1861
presentations
to
land
owner
200-500m
3079
1241
organisations
throughout
2010.
500-1000m
2378
620
Maintenance cost / year / plot owner
However, the financing model has been
0-200m
2834
372
rejected at a public hearing in June
200-500m
3079
248
2011. At present it is undecided if the
500-1000m
2378
124
project will go ahead. Alternatively, the
project could be financed by all land owners in the municipality through an extra real estate
tax. The nourishment project is currently in a political process awaiting the final decision.
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Christian Helledie
Table 4 Comparison of cost of nourishment schemes at the inner Danish waters
Initial cost DKK/km ex. VAT
Maintenance cost DKK/km/year ex. VAT
Funen
Liseleje
Gribskov Municipality
Included in
yearly cost
4,100,000
1,200,000*
230,000
150,000
100,000*
* estimated
Financial Comparison of Nourishment Schemes
Table 4 shows a comparison of the cost of development and maintenance of the beach
nourishment schemes at the inner Danish Waters. The coastal protection scheme at Funen has
been developed over the years and large initial capital investment has therefore been avoided.
Thereby the project economy and the protection scheme have been optimised. The scheme at
Liseleje had a large initial cost as hard coastal protection was included initially. Then the
coastal protection and the recreational value was optimised form the beginning. However,
maintenance is also required for this type of scheme. The cost of the project is relatively large,
as the length of the project is small and the coast more exposed. A cost effective scheme can
be achieved by focusing on large scale beach nourishment as in Gribskov Municipality.
However, this scheme may require additional investment in revetments and breakwaters to
protect the hinterland and beach, which is the responsibility of plot owners along the cliffs.
Conclusion and Recommendations
Beach nourishment can re-establish sandy shores at the inner Danish waters and hereby
increase protection of the hinterland and create recreational value. However, beach
nourishment shall be maintained. Revetments are often required to protect the hinterland
against storm impact and beach breakwaters are required at exposed locations to stabilise the
sandy beaches. There is a large need for rehabilitation of old ineffective shore protection
structures at the inner Danish waters. Small private coastal protection associations are often
responsible for maintaining the coastal protection structures, but due to limited funding and
lack of coordination shore protection structures are often ineffective and have an un-aesthetic
appearance. This has often resulted in beach erosion and thus reduced recreational value of
the coast. Accepting the presence of old ineffective shore protection structures may in some
cases be necessary in order to implement regional beach nourishment schemes. However, the
best option is to coordinate shore rehabilitation projects at regional scale and include the old
coastal protection structures as well as large scale beach nourishment initially. Funding is the
most critical factor for successful implementation of shore rehabilitation projects. Beach
nourishment shall preferably be financed by large group of citizens as it creates recreational
value for many as well as increasing protection of the coast. Hereby the costs can be split and
thus become acceptable for all. The municipality shall coordinate the regional beach
nourishment projects initially, but private coastal protection associations can be responsible
for implementation and long term maintenance of large beach nourishment schemes.
Acknowledgement
Thanks to Mogens Stougaard from Funen and Frits Taulow from Liseleje for providing data
and background information. Also thanks to Per Sørensen from DCA, Joergen Juhl and Ole
Juul Jensen from COWI for reviewing the paper.
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