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Costs of Adapting Coastal Defences to Sea-Level Rise— New Estimates and Their Implications


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The cost of upgrading and raising coastal defences is an important consideration in societal response to sea-level rise. Currently available unit cost estimates have a limited empirical basis. This article presents new information on the unit costs of adapting coastal defences for three specific case studies in low-lying delta regions: The Netherlands, New Orleans, and Vietnam. Typical measures include dikes, flood walls, storm surge barriers, and nourishment. These unit cost estimates are significantly higher than earlier estimates that are still the main source of costs for global vulnerability assessments. Factors affecting these unit costs include local economic factors (material and labour costs), design choices related to the alignment of the system, and the types of measures for implementation of the system in an urban or rural environment. On the basis of an example for a Dutch sea dike, it is shown that the material quantities and associated costs are expected to rise linearly, in the case of depth-limited wave breaking, for the range of sea-level rise rates that are expected in the coming century. However, other factors, such as increasing costs for implementation of wider coastal defences in an urban environment and future changes in material and labour costs, could contribute to a nonlinear increase of the costs. Further collection and analysis of project information for coastal defence projects in other regions is recommended to strengthen the empirical basis of the cost estimates that are used for regional and global assessments.
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Costs of Adapting Coastal Defences to Sea-Level Rise— New Estimates and Their
Author(s): Sebastiaan N. Jonkman, Marten M. Hillen, Robert J. Nicholls, Wim Kanning, and Mathijs van
Source: Journal of Coastal Research, 29(5):1212-1226.
Published By: Coastal Education and Research Foundation
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Costs of Adapting Coastal Defences to Sea-Level Rise—
New Estimates and Their Implications
Sebastiaan N. Jonkman
, Marten M. Hillen
, Robert J. Nicholls
, Wim Kanning
, and
Mathijs van Ledden
Delft University of Technology
Faculty of Civil Engineering and Geosciences
Section of Hydraulic Engineering
Stevinweg 1
2628 CN, Delft, The Netherlands
Royal HaskoningDHV
Business Line Rivers, Deltas, and Coasts
Rotterdam, The Netherlands
University of Southampton
School of Civil Engineering and the Environment
Southampton, SO17 1BJ, United Kingdom
Rotterdamseweg 185
2629 HD Delft, the Netherlands
Jonkman, S.N.; Hillen, M.M.; Nicholls, R.J.; Kanning, W., and van Ledden, M., 2013. Costs of adapting coastal defences
to sea-level rise—new estimates and their implications. Journal of Coastal Research, 29(5), 1212–1226. Coconut Creek
(Florida), ISSN 0749-0208.
The cost of upgrading and raising coastal defences is an important consideration in societal response to sea-level rise.
Currently available unit cost estimates have a limited empirical basis. This article presents new information on the unit
costs of adapting coastal defences for three specific case studies in low-lying delta regions: The Netherlands, New
Orleans, and Vietnam. Typical measures include dikes, flood walls, storm surge barriers, and nourishment. These unit
cost estimates are significantly higher than earlier estimates that are still the main source of costs for global
vulnerability assessments. Factors affecting these unit costs include local economic factors (material and labour costs),
design choices related to the alignment of the system, and the types of measures for implementation of the system in an
urban or rural environment. On the basis of an example for a Dutch sea dike, it is shown that the material quantities and
associated costs are expected to rise linearly, in the case of depth-limited wave breaking, for the range of sea-level rise
rates that are expected in the coming century. However, other factors, such as increasing costs for implementation of
wider coastal defences in an urban environment and future changes in material and labour costs, could contribute to a
nonlinear increase of the costs. Further collection and analysis of project information for coastal defence projects in other
regions is recommended to strengthen the empirical basis of the cost estimates that are used for regional and global
ADDITIONAL INDEX WORDS: Climate adaptation, engineering measures, dikes, flood protection, storm surge
barriers, sea-level rise, unit costs.
A large and rapidly growing part of the world’s population
lives in low-lying coastal zones (Small and Nicholls, 2003).
Urban areas are a large and growing part of this exposure
(Hanson et al., 2011; Nicholls et al., 2008). To sustain
habitation and economic activities in coastal areas, a wide
range of coastal defence measures has been constructed. These
measures reduce the risk to populations and economic values in
coastal zones prone to flooding. Climate change, and more
specifically climate-induced sea-level rise, as well as subsi-
dence where appropriate, pose a direct threat to these areas
(Nicholls, 2010; Nicholls et al., 2007). Sea-level rise requires
that coastal defence measures be adapted to higher water
levels, and the effects of climate change could lead to more
intense hydraulic boundary conditions, such as waves and
storm surges. In this article, we consider the costs of adapting
coastal defences to relative sea-level rise (i.e. the combination of
climate-induced sea-level rise and subsidence). Important
elements of adaptation to sea-level rise and climate change
that are not discussed in detail in this article are the changes in
sediment load in rivers, land use patterns, and economic and
population growth.
Various studies (e.g.Tituset al., 1991; Yohe et al., 1996)
provide general insight in the effects of sea-level rise, the costs
of effects such as land loss, and mitigation measures such as
land elevation and structure relocation. However, to assess the
broad-scale implications of sea-level rise realistically, including
adaptation costs and feasibility, unit cost estimates of upgrad-
ing coastal defences are required. The unit costs of dikes and
other related coastal defence measures that are typically used
in low-lying delta areas have previously been estimated at a
DOI: 10.2112/JCOASTRES-D-12-00230.1 received 9 November 2012;
accepted in revision 24 February 2013; corrected proofs received
29 March 2013.
Published Pre-print online 19 April 2013.
Ó Coastal Education & Research Foundation 2013
Coconut Creek, Florida September 2013Journal of Coastal Research 29 5 1212–1226
global scale by the Intergovernmental Panel on Climate
Change Coastal Zone Management Subgroup (IPCC CZMS,
1990) and Hoozemans, Marchand, and Pennekamp (1993), and
more recently by Linham, Green, and Nicholls (2010). Despite
being produced more than 15 years ago, the unit cost estimates
from IPCC and Hoozemans, Marchand, and Pennekamp (1993)
remain the main source of unit cost data in global vulnerability
assessments such as the Framework for Uncertainty, Negoti-
ation, and Distribution (FUND; Tol, 1997), the Dynamic
Interactive Vulnerability Assessment (DIVA; Hinkel, 2005;
Sugiyama, Nicholls, and Vafeidis, 2008), and Sugiyama,
Nicholls, and Vafeidis (2008).
Therefore, the empirical basis for these global studies needs
to be improved with recent available data on the costs of coastal
defence projects from various regions. The present study aims
to provide new empirical information on the costs of adaptation
of coastal defences to sea-level rise. The study focuses on low-
lying delta areas, since sea-level rise is an important threat for
these coastal regions. Because of the low-lying topography, it is
expected that coastal defence and adaptation measures need to
be applied on a large scale in deltas. Therefore the costs of
coastal adaptation measures will be specifically high for these
regions. The study analyzes cost information from three
specific case studies that represent low-lying delta areas (The
Netherlands, New Orleans, and Vietnam). This study investi-
gates the unit cost estimates of coastal defence for a range of
hard and soft engineering measures, such as dikes/levees, sea
walls, (beach) nourishments, and storm surge barriers. Despite
their importance for delta areas, information on the costs of
these types of measures globally is especially deficient
(Linham, Green, and Nicholls, 2010).
Different scale levels can be distinguished in the assessment
of costs of adaptation of coastal defences to climate change. At
the highest level of detail, specific information from the
construction costs of actual projects can be utilized. This
requires detailed insight into the design and construction of
coastal defence projects. By combining information from
individual projects, cost estimates can be provided for one
enclosed coastal defence system for a city or region, such as a
flood protection system for New Orleans. Cost estimates at a
national level can be obtained by aggregating information from
different defence systems within a country. For example, Kok
et al. (2008) report estimates of the costs at the national level
for the adaptation of flood defences in The Netherlands to
different levels of sea-level rise. Finally, estimates for different
systems and countries can be aggregated to cost estimates at a
regional, continental, or even global level (e.g. Hoozemans,
Marchand, and Pennekamp, 1993; IPCC CZMS, 1990). It is
important that these higher level cost estimates are based on
realistic information at the project and system level. Project-
level costs frequently are not considered in sea-level rise
studies and provide a good basis to update unit costs
determined in the 1990s.
The aim of this study is therefore to use project- and system-
based estimates to strengthen the empirical foundation of cost
estimates at a regional and global level.
The present study has been reported in more detail in the
research report of Hillen et al. (2010) and was part of a larger
study on the costs of adaptation to the effects of climate change
in the world’s largest port cities (Linham, Green, and Nicholls,
For this study, project-based cost estimates for three case
study areas are obtained. They represent similar coastal types
(i.e. a low-lying deltaic coast) that are vulnerable to sea-level
rise and subsidence. The reported measures reflect typical
defence measures to reduce flood risks in coastal areas: dikes,
floodwalls, nourishments, and storm surge barriers. In all
cases, storms could lead to extreme sea levels and threaten
coastal defences. In New Orleans and Vietnam, these extreme
events are caused by tropical depressions (hurricanes, ty-
phoons, cyclones) and in The Netherlands, by extratropical
storms in the form of storm surges on the North Sea.
There are differences in the standards of protection (the
return period associated with the hydraulic conditions that the
coastal defences should be able to withstand safely) and the
corresponding surge levels and wave heights. These charac-
teristics are summarized in Table 1. Additionally, the three
case study areas reflect different economic and social situa-
tions. The Netherlands and New Orleans can be characterized
as urbanized areas in economically highly developed delta
regions. The large differences in the standard of protection
between these two case studies reflects different societal
attitudes to risks and willingness to pay in the two countries.
Large parts of coastal Vietnam can be considered rural areas in
a developing economy.
The general approach followed in the study consisted of three
steps (see Hillen et al. [2010] for further background). First,
project-based information on coastal defence measures and
costs was collected for the three areas and measures within the
scope of the study (see above). Second, because the information
was presented in different ways in the underlying studies, the
types of measures and cost numbers were analyzed and
converted to comparable units. Third, to compare the unit
costs, they were converted to the same currency (Euros, E)and
the same reference year. The costs presented in this article are
expressed in price levels for the year 2009. For The Nether-
lands, the costs have been corrected by an average 4% growth
rate of the general construction costs (Statistics Netherlands,
2011). The reported costs for New Orleans and Vietnam are
mostly for 2009 and 2010 and have therefore not been
corrected. Where U.S. dollars were used in the original
references, a conversion rate of E1 ¼ US$1.35 was applied.
More details on the flood defence system, geography, typical
coastal measures, and references to the original sources of unit
cost estimates for the case studies are provided in the sections
that follow.
The Netherlands
The Netherlands is situated in northwest Europe. About one-
quarter of the country is below sea level, and more than half of
the country is situated below normal high tides. Several flood
defence measures such as coastal and river dikes, storm surge
barriers, dams, and sand dunes form the flood defence systems
that protect most of The Netherlands from flooding. An
Journal of Coastal Research, Vol. 29, No. 5, 2013
Costs of Adaptation to Sea-Level Rise 1213
example of a typical cross section of a coastal dike is shown in
Figure 1.
Well-known coastal defence structures in The Netherlands
are the Deltaworks, an extensive system of dikes and storm
surge barriers that protect the southwestern delta, built after
the catastrophic flooding of 1953 (McRobie, Spencer, and
Gerritsen, 2005). In addition to structural coastal defence
measures, beach nourishments are applied along the Dutch
open (wave-exposed) coastline, which helps sustain the sandy
beaches and dunes that here provide the main defence (Van
Koningsveld et al., 2008).
For The Netherlands, several studies have been conducted to
assess the costs of adaptation of flood defences. As part of a cost-
benefit analysis, ARCADIS and Fugro (2006) assessed the costs
of adaptation of coastal dikes along the North Sea coast and in
the estuaries in the southwestern part of the country. Within
the same study, Eijgenraam (2006) reported dike reinforce-
ment costs for more urbanized areas in the southwest of the
Sand nourishments are the preferred strategy for the sandy
parts of the Dutch coast. Because of the large resources of
nourishment material and the large volume of beach nourish-
ment in The Netherlands, the unit costs of nourishments used
to be relatively low, at around E3/m
of nourishment
(ARCADIS and Fugro, 2006; Kok et al., 2008). However, the
cost of nourishment has increased rapidly (more than 200%)
over the last 5 years (Algemene Rekenkamer, 2009; Rijkswa-
terstaat, 2009). The increase in costs can be partly related to oil
prices and partly to a market situation characterized by a
limited number of large contractors.
New Orleans
New Orleans is situated in the delta of the Mississippi River.
The city originated along the natural levees (higher grounds)
along the Mississippi river, but later development expanded
across the low-lying marshes that are now largely below sea
level (Grossi and Muir-Wood, 2006). As a consequence of its
geographical situation, the area is vulnerable to flooding from
tropical depressions (hurricanes), high discharges down the
Mississippi River, and heavy rains. Levees (a synonym used in
the United States for dikes) protect the city from flooding from
hurricanes and high discharges from the Mississippi river.
Large-scale pumping systems are installed to remove rainfall
from the city.
The vulnerability to flooding from hurricanes was tragically
shown when large parts of the city flooded from the effects of
hurricane Katrina in the year 2005 (e.g. Grossi and Muir-Wood,
2006). This event led to enormous damage and more than 1100
fatalities (Jonkman et al., 2009). A subsequent large-scale
program for improvement and repair of the hurricane
protection system to a safety standard of 1/100 per year was
set up with a total budget of approximately US$14 billion. An
overview of the current New Orleans flood protection system is
given in Figure 2. It has a total length of 392 km and consists of
earthen levees along the river (185 km) and earthen levees,
floodwalls, and storm surge barriers (207 km) along the lakes to
protect the city against hurricanes. Additionally, the wetlands
can be regarded as part of a natural storm surge defence system
because the marshes dissipate storm surges (Resio and West-
erink, 2008).
Typical sketches of cross sections are presented for a
floodwall (T-type wall, Figure 3) and an earthen levee (Figure
4). An important design element for the floodwalls is the sheet
piling under the concrete wall that prevents seepage and piping
and provides stability. A number of important failures during
hurricane Katrina occurred because of an insufficient length of
these sheet pilings (Seed et al., 2006).
Table 1. Overview of the main characteristics of the three case study areas
Standard of
(per y)
Surge Level
for Design
Conditions (m)
Wave Height
for Design
Conditions (m)
The Netherlands 1/4000–1/10,000 4–6 4–10
New Orleans (USA) 1/100 3–6 1–2.5
Vietnam 1/50
3–5 2–3
Average significant wave height; could vary 61 m depending on the
Estimate based on Mai (2010).
Figure 1. Schematic cross section of a typical sea dike in The Netherlands.
Journal of Coastal Research, Vol. 29, No. 5, 2013
1214 Jonkman et al.
Several sources give insight into estimated and actual costs
of adaptation of the flood defences around New Orleans after
hurricane Katrina. Project information on the costs of several
component projects of the New Orleans hurricane protection
system is provided at an interactive United States Army Corps
of Engineers website (USACE, 2009). This defines the costs,
length, and type of structure for individual projects. For this
study, a representative sample of 17 projects was analyzed. The
projects concerned raising of earthen levees, construction of
(new) floodwalls, and strengthening and adaptation of existing
levee/floodwall structures. The underlying project data and
ranges in unit costs per type of construction are reported in the
Appendix table. The results show that the unit costs of concrete
floodwalls (E5–9 million/km per meter raising [ME/km per m
raising]) are relatively high when compared with unit costs for
earthen levees (ME2.5–5/km per m raising). Reasons for
selecting concrete floodwalls might include (1) the smaller
footprint of levees with floodwalls, (2) the scarcity of material
such as clay that would be needed for the construction of
Figure 2. Overview of the New Orleans Hurricane and Storm Damage Risk Reduction System.
Figure 3. Schematic cross section of typical coastal protection structures in
New Orleans: T-wall (based on IPET, 2007).
Figure 4. Schematic cross section of typical coastal protection structures in
New Orleans: hurricane levee (based on IPET, 2007)
Journal of Coastal Research, Vol. 29, No. 5, 2013
Costs of Adaptation to Sea-Level Rise 1215
earthen levees, and (3) the resilience that these concrete
structures provide during extreme wave overtopping condi-
tions when properly protected on the inner side.
A number of earlier studies by Dutch experts and organiza-
tions included cost estimates for New Orleans for concrete
floodwalls (Bos, 2008), earthen levees, and stabilization and
creation of marshlands (Dijkman, 2007; USACE, 2009).
Vietnam has two major river deltas, the Red River delta in
the North and the Mekong delta in the South, and a relatively
long coastline, which measures 3260 km. The coastal areas of
Vietnam are subject to almost annual flooding from tropical
depressions (typhoons) formed in the South China Sea. The
river deltas are the most densely populated areas of Vietnam
and are prone to flooding from both the rivers and the sea (Mai
et al., 2009; Pilarczyk and Nuoi, 2002). The current state of
many of the sea dikes is far from optimal, as demonstrated by
the nearly decadal breaches of sea dikes in the northern coastal
provinces of Vietnam (Mai, 2010).
Hardly any land lies below sea level in Vietnam. Dikes are
constructed to prevent flooding because of high river levels,
typhoons (surges), and heavy rainfall flooding and to combat
erosion of coastal areas (Mai et al., 2009). The amount of public
information on costs of coastal defences in Vietnam is scarce,
and estimates are based on basic calculations, expert judge-
ment, and interviews.
Hillen (2008), Mai (2010), and Mai et al. (2008) determined
the costs of coastal dike raising for rural areas in Nam Dinh
province in an effort to illustrate a comparable probabilistic
approach to determining safety standards for Vietnam.
Estimates were based on the construction of new sea dikes
that have been and are being constructed in northern Vietnam
in rural areas. These dikes consist of a sand and clay body and
have revetments on the sea side. The dikes are up to 8 m high,
and a typical profile is shown in Figure 5.
Unit Costs of Coastal Defence Measures
Table 2 summarizes the unit cost estimates based on
information from the three case studies. A distinction is made
between the capital costs of upgrading and raising coastal
defences, beach and shore nourishments, and other costs such
as dike maintenance and marshland stabilization. The costs of
another coastal defence measure, storm surge barriers, that
Figure 5. A representative cross section of a sea dike in Nam Dinh province
(northern Vietnam; adjusted from Mai et al., 2008).
Table 2. Unit costs of coastal defence measures, converted to 2009 price levels, and sources.
Country (Region) Defence (ME/km per m) Nourishment (E/m
material) Other Measures
The Netherlands Dike raising, rural 2.3–6.7 Stive, personal communication Maintenance of flood defences ME0.1/km per y AFPM, 2006
9.4–11.2 Kok et al., 2008 3 Kok et al., 2008
4.5–12.4 Eijgenraam, 2006 3.2 ARCADIS and Fugro, 2006
7.8 ARCADIS and Fugro, 2006
Dike raising, urban
18.7–22.4 Kok et al., 2008 3.7, shore RWS, 2009
15.5 ARCADIS and Fugro, 2006 7.5, beach RWS, 2009
United States (New
Earthen dike raising - Marshland stabilization E1.4/m
Dijkman, 2007
5–8 Dijkman, 2007; Jonkman et al.,
Marshland creation E3/m
Dijkman, 2007
2.5–5 USACE data 2011 Freshwater diversion/
ME10 Dijkman, 2007
T-wall floodwall construction
4.9–11.8 USACE data 2011
3.7–4.5 Bos, 2008
Floodwall/levee raising and strengthening
various measures, costs per km
4.4–9.1 USACE data 2011
Vietnam (Hai Phong/ Dike raising, rural - Dike maintenance ME0.02/km Hillen, 2008;
Nam Dinh) 0.7–1.2 Hillen, 2008 dike per y Mai et al., 2008
0.75 Mai et al., 2008
Journal of Coastal Research, Vol. 29, No. 5, 2013
1216 Jonkman et al.
might become more widely applied given sea-level rise are
analysed in more detail in the next section. The reported costs
concern the upgrading of coastal defence structures, including
costs for related processes such as engineering and obtaining
For The Netherlands, the unit costs of strengthening dikes
range between ME15.5 and ME22.4/km per m raising for urban
areas, and ME4.5 and ME12.4/km per m raising for rural areas
(2009 price levels). The unit costs for strengthening the levees
of New Orleans are somewhat less, between ME2.5 and ME5/
km per m raising for earthen levees and ME4.9 and ME11.8/km
per m height for constructing concrete floodwalls. Floodwalls
are expected to be more difficult to raise incrementally than
earthen dikes, so the costs for future reinforcements of
floodwalls will be higher than the current estimates. The costs
for raising dikes in Vietnam are less, likely because of local
economic factors, such as the costs of labour. For beach
nourishment in The Netherlands, the available literature
sources indicate a unit cost price of about E3–4/m
of material
for shore nourishment and E7–8/m
of material for beach
nourishment. For The Netherlands (AFPM, 2006) and Viet-
nam, estimates are available for the management and
maintenance costs, and for both countries, the costs are about
1%–2% of the typical unit costs of raising the defences.
These insights can be used for further derivation of national,
regional, and global indicators for assessing the costs of
adapting coastal defences to sea-level rise.
Storm Surge Barriers
Storm surge barriers are floodgate systems that allow water
to pass under normal circumstances but can be closed when a
(storm) surge is expected. They have been constructed as part
of the coastal defence system at various locations around the
world (e.g. Gilbert and Horner, 1984), usually in developed
countries (Linham and Nicholls, 2010). Storm surge barriers
are often chosen as a preferred alternative to close off estuaries
and reduce the required length of dike strengthening behind
the barriers. Another important characteristic is that they are
often (partly) opened during normal conditions to allow for
navigation and saltwater exchange with the estuarine areas
landward of the barrier. Famous examples are the storm surge
barriers in The Netherlands in the southwest of the country
(Figure 6). In New Orleans, several storm surge barriers have
been built after Katrina to protect the city from surges and
reduce the length of the directly exposed system. A global
assessment of a selection of planned and constructed barriers
has been performed. An overview of the main characteristics of
these storm surge barriers is given in Table 3.
The costs of a storm surge barrier depend on many factors,
including the type of barrier and gates, the local soil
characteristics, the desired height, and the hydraulic head. A
first range of unit cost prices per unit width has been deduced
from the available data. This unit cost price ranges between
ME0.5 and ME2.7/m width. The management and mainte-
nance costs of complex storm surge barriers are relatively high,
and these costs have been estimated at 5%–10% of the
construction costs (Nicholls, Cooper, and Townsend, 2007).
Comparison with Studies from the 1990s
To quantify the implications of sea-level rise at a global level,
generic unit cost prices of coastal defence measures have been
determined and applied by IPCC CZMS (1990) and improved
by Hoozemans, Marchand, and Pennekamp (1993) to reflect the
national ‘‘ sea-level rise regime.’’ In both studies the costs of a
number of typical coastal defence measures were calculated on
the basis of coastal defence measures as applied in The
Netherlands and assumed standard dimensions. Assuming
material costs and construction costs, ‘‘ all-in’’ costs were
determined for adapting several coastal defence measures to
a uniform scenario of a 1-m global sea-level rise. These all-in
Figure 6. Maeslant storm surge barrier (near Rotterdam) and the Eastern Scheldt barrier (source: Rijkswaterstaat, 2009).
Journal of Coastal Research, Vol. 29, No. 5, 2013
Costs of Adaptation to Sea-Level Rise 1217
costs include design, construction, taxes, and fees. Royalties
and financing costs were not taken into account.
Hoozemans, Marchand, and Pennekamp (1993) improved
some of these cost estimates, building on the methods and
results from IPCC CZMS (1990). Increased wave run-up and
the resulting costs of adapting the defences to a higher design
height were included as additional factors. Hoozemans, March-
and, and Pennekamp (1993) determined the costs for a 5-m-
high defence and developed continuous cost functions for three
types of coastal defence measures: stone-protected sea dike, a
clay-covered sea dike, and a sand dune (Figure 7). Theunit
costs for increasing the height of the defences by 1 m are
reflected by the steepness of the curves in the figure and are
ME2.5/km per m raising (2009 price levels) for all three
Both previous studies base their unit cost estimates on the
Dutch situation. Table 4 summarizes the unit costs of the
studies and presents the comparison with the more recent unit
costs for The Netherlands from this study.
Table 4 shows that the unit cost estimates for sea dikes found
in this study are significantly higher than those from IPCC
CZMS (1990) and Hoozemans, Marchand, and Pennekamp
(1993). While recent actual costs estimates for The Netherlands
were in the range ME4.5–12.4/km length per m raising for
rural areas, IPCC CZMS (1990) found ME0.8–1.6/km per m
and Hoozemans, Marchand, and Pennekamp (1993) ME2.6/km
per m. The difference is smaller for strengthening of sea dikes
in urban areas, where IPCC reported ME16.2/(m km), and this
study found a range of ME15.5–22.4/(m km).
The earlier studies based their estimates on the Dutch
situation, but this seems to focus on basic idealized earthen
structures and therefore underestimated the average costs of
actual dike raising. The analysis of actual project data in this
study resulted in higher all-in costs, reflecting real situations
where nonideal situations are common. Unit cost estimates for
coastal defences should account for these additional costs that
are always included in large engineering projects.
Comparison with Recent Cost Estimates from Other
In a recent study on costs of adaptation (Linham, Green, and
Nicholls, 2010), unit cost estimates for coastal protection
measures in some other countries and regions have been
presented, for example, for the United Kingdom, Germany,
Australia, and California. In that overview, especially, infor-
mation for vertical seawalls, beach nourishments, and land
reclamation is included. The cost estimates in Linham, Green,
and Nicholls (2010) are to a large degree based on expert
judgement. The data basis of these estimates is therefore not
fully comparable with the more project-based data presented in
Figure 7. Cost functions for three coastal defence measures for The
Netherlands (from Hoozemans, Marchand, and Pennekamp, 1993).
Table 3. An overview of storm surge barriers around the world.
Name of Barrier Type Year
Costs (ME)
2009 Price
Level (ME)
Unit Cost
(ME/m width)
The Netherlands
Maeslant barrier (New Waterway,
Floating sector gate 1997 360 22 5 450 656 1.82
Hartel barrier (Hartel channel) Vertical lifting gates 1997 170 9.3 5.5 98 143 0.84
Eastern Scheldt Barrier Vertical lifting gates 1986 2400 14 5 2500 4021 1.68
Ramspol (near IJssel Lake) Bellow barrier 2001 240 8.2 4.4 100 132 0.55
Ems (Germany) Sector gates 2002 360 8.5 3.8 290 368 1.02
Thames (Great-Britain) Sector gates 1984 530 17 7.2 800 1449 2.73
St. Petersburg (Russia) Floating sector gate 2011 200 16 4.2 n.a.
Vertical lifting gate 100 7 4.2
Venice MOSE project (Italy) Flap gates 2012 3200 15 3 4678 4678 1.46
New Orleans
Seabrook barrier Vertical lifting gates and
sector gates
2012 130 8 4 114.7 115 0.88
IHNC barrier—only gates (excl.
Sector gates 2011 250 8 4 518 518 2.07
Remarks: (1) Year when the barrier is or is expected to be commissioned; (2) For the IHNC/storm surge barrier, only the parts containing the gates have
been considered, and the floodwall costs were excluded.
Journal of Coastal Research, Vol. 29, No. 5, 2013
1218 Jonkman et al.
this article for The Netherlands, New Orleans, and Vietnam. A
comparison of unit costs from the two studies is shown in Table
The costs for nourishments for The Netherlands are similar
to costs obtained from expert judgement for many other
regions. For New Zealand and the United Kingdom, the upper
values of the reported ranges are rather high, likely because of
the lack of available sand at some locations. For earthen dikes,
the unit costs found in this study for The Netherlands and New
Orleans are higher than the reported unit costs for the United
Kingdom and California in Linham, Green, and Nicholls
(2010). One of the reasons for this difference could be that
actual project costs (used in this study) are often higher than
cost estimates for idealized cross sections that are used in
various other studies. For nourishments there seems to be a
considerable amount of accessible information. For other
important defence types, such as dikes and floodwalls,
information on unit costs is especially deficient.
In this section, we discuss the factors that affect unit costs for
individual sections of coastal defences and the resulting costs at
the system level.
Factors Affecting Unit Costs
Five cost factors mainly determine the unit costs of coastal
defences: planning and engineering, material, labour, imple-
mentation, and management and maintenance costs. The
capital costs constitute planning and engineering to imple-
mentation, whereas the management and maintenance costs
are an ongoing annual stream of costs required to sustain an
effective defence system. These are discussed in more detail
Planning and Engineering Costs
This concerns the design and planning of the coastal defence. In
the case of large uniform sections in rural areas, these unit
costs may be relatively low, while in residential areas with non-
uniform and complex conditions, these unit costs are relatively
Material Costs. The typical materials for construction of sea
defences include sand, clay, rock, and concrete, and the costs of
Table 4. A comparison of unit costs as determined by IPCC CZMS (1990) and Hoozemans, Marchand, and Pennekamp (1993) with cost estimates from this
study for The Netherlands (in 2009 prices).
Adaptation Measure
Previous Studies
This Study, 2009 price
level (E)
Study Original Price Level ($) 2009 Price Level (E)
Construction of sea dike
IPCC CZMS M$0.4/km ME0.6/km -
With maintenance: M$0.6/km With maintenance: ME1.0/km
Raising low sea dikes by
1 m in rural areas
IPCC CZMS M$0.5/km ME0.8/km ME4.5–12.4/km per m
Raising high sea dikes by
1 m in rural areas
IPCC CZMS M$1/km ME1.6/km
Stone protected sea dike
Hoozemans, Marchand, and
M$4.5–8.5/km ME6.8–12.8/km
Clay-covered sea dike Hoozemans, Marchand, and
M$2.5/km ME3.8/km
Raising sea dikes by 1 m
in urban areas
IPCC CZMS M$10/km ME16.2/km ME15.5–22.4/km per m
Closure dams IPCC CZMS M$15–25/km ME24.3–40.6/km -
Beach nourishment IPCC CZMS $3–6/m
E4.9–9.7 /m
Sand dune Hoozemans, Marchand, and
M$4.5/km ME6.8/km -
Raising industrial areas
and harbours by 1 m
Raising island elevation
by 1 m
IPCC CZMS M$12.5/km
The original data has been converted to 2009 prices (in Euros [E])with a discount rate of 4% and an exchange rate of E1 ¼US$1.35.
Depends on the depth of the toe on outer slope of the dike (see Figure 7).
Table 5. A comparison of unit costs for The Netherlands, New Orleans, and
Vietnam from this study with cost estimates for other countries from
Linham, Green, and Nicholls (2010) (in 2009 prices).
Measure This Study
Other Regions
(Linham, Green,
and Nicholls, 2010)
The Netherlands
Foreshore: 3–4
Beach: 7–8
Australia: 5
France: 4–6
Germany: 4–8
Italy: 5–6
New Zealand: 7–54
South Africa: 11
Spain: 4–7
United Kingdom: 3–34
USA (California): 6–12
Raising earthen
dikes (ME/km
per m)
Netherlands, Rural:
Netherlands, Urban:
New Orleans: 2.5–5
Vietnam: 0.7–1.2
United Kingdom: 0.7–3.8
USA (California): 0.6–2.7
Floodwall (ME/
km per m)
New Orleans: 4.9–
Mozambique: 0.7
Journal of Coastal Research, Vol. 29, No. 5, 2013
Costs of Adaptation to Sea-Level Rise 1219
these materials depend on local and regional market prices. In
deltaic regions, there is sometimes a scarcity of construction
materials, especially if large-scale programs are executed.
Hence, material costs could strongly influence the unit price of
different measures and the type of construction that is selected.
Labour Costs. Costs of labour vary widely between countries.
However, when the cost of labour is low, labour is used more
intensely, whereas in the case of expensive labour, mechanized
equipment is more widely applied.
Implementation Costs. Implementation costs are mainly
linked to two main factors: (1) Land use by flood defences.
The land width required for flood defence usually increases
linearly with height. Obtaining this land could be financially
and legally challenging, and thus a costly and time-consuming
task. This is more problematic in urban than rural areas. (2)
Rural or urban implementation. In an urban environment,
space is usually scarce and standard solutions for raising flood
protection would require removal of parts of the urban
environment. Experience suggests that this is strongly resist-
ed, and alternative space-saving solutions are needed that can
raise the cost substantially. Such solutions (e.g. sheet pilings or
cutoff walls) are usually more expensive than the relatively
cheap raising of earthen dikes in rural areas.
The costs of a project will depend on the exact solution
chosen. The choice of a measure will never be based solely on
flood defence requirements. The flood defence function (and its
cost) will only form part of the total project. Other functions
(recreation, infrastructure, ecological quality, etc.) will influ-
ence the design as well. Multifunctional and integrated
approaches are becoming more and more common, and the
total costs of these solutions would be generally higher than in
the case for the flood defence function alone. Examples of such
solutions include the Room for the Rivers program in The
Netherlands and multifunctional dikes. Instead of heightening
the river dikes, the Room for the Rivers program has been
adopted, in which ecological and landscape issues are impor-
tant factors (Van Stokkom, Smits, and Van Leuven, 2005). This
strategy is generally more expensive than strengthening the
dikes. In Japan, construction of so-called ‘‘super levees’’—wide
(coastal) dikes that have a very low residual risk—are also used
for urban development (Takeuchi, 2002).
Management and Maintenance Costs
Proper management and maintenance of defences is essential
and represents an ongoing annual cost: poor management and
maintenance increases the risk of defence failures. The costs of
maintenance will include small operations and reparations on
the coastal defences, such as maintenance of storm surge
barriers and regular inspection. Additionally, an organization
is needed for the management and maintenance of flood
defences, requiring additional annual costs to maintain.
Management and maintenance in The Netherlands is carried
out by so-called Water Boards. In other countries, there are also
usually (semi-)governmental bodies for management and
maintenance. Management and maintenance costs are expect-
ed to be largely independent of sea-level rise, in that the
existing dike system needs to be managed and maintained as
well. On the basis of the Vietnam and The Netherlands studies
these costs are 1%–2% of the upgrade costs per year. However,
these costs could increase when more complex structures, such
as storm surge barriers, are included in the coastal system as a
response to sea-level rise.
Comparison of Unit Costs Between Countries
The unit costs in a region will be influenced by local economic
factors, such as the costs of labour and materials and the use of
equipment. The contribution of the categories to the unit price
is likely to differ between countries. These economic factors will
also affect the selected design, the materials used, and the
construction method.
The relationship between economic factors and unit cost
prices has been investigated for the case studies. The costs of
raising coastal defences in rural areas are in the same range for
The Netherlands and New Orleans (see Table 2). The Nether-
lands and the United States have a similar GDP per capita. The
costs of raising coastal defences and the GDP per capita are
significantly lower in Vietnam. Analysis of additional informa-
tion for other countries is recommended to investigate whether
there is a relationship between the unit costs for coastal
protection measures in various countries and the GDP per
capita or other economic indicators. In other fields of civil
engineering, international construction cost surveys are
available that compare the general trends in the construction
industry; the costs of structures, such as houses and hotels; and
material quantities, but not in the field of coastal management
(Turner and Townsend, 2012).
IPCC CZMS (1990) and Hoozemans, Marchand, and Penne-
kamp (1993) multiplied the Dutch cost estimates by a country
factor to assess the unit costs for all other countries. The
following six factors taken into account in the derivation of a
country factor were: (1) the presence of a ‘‘ wet’’ civil
construction industry, (2) availability and costs of human
resources, (3) availability and quality of construction material,
(4) possibility for mobilization of equipment, (5) possible effects
of the size of the project, and (6) acquisition costs (land) for the
local market situation. For simplicity, the country cost factors
were determined per continent via a selection of several
classes. In the IPCC CZMS (1990) study, the country factor
for Vietnam was 1.0 (for the low coastal areas) and 1.5 for the
other coastal areas (cities, beach areas, and other infrastruc-
ture). For the United States, a county cost factor of 2.0 was
applied. Comparison with the actual cost estimates obtained in
this study produces smaller country factors relative to The
Netherlands: 0.63 for New Orleans (United States) and 0.13 for
The country cost factors from IPCC CZMS (1990) attempt to
take into account the local conditions but overestimate the
actual costs for both Vietnam and the United States. However,
the method for deriving country factors does not sufficiently
take into account the effect of local construction price levels.
This underlines the need to use actual project data for deriving
unit cost estimates as much as possible.
Cost Estimates at a System Level
The total cost for adaptation of a flood defence system is
determined by the unit cost prices for individual reaches
(discussed in previous sections) and the length of the flood
defences in the system. Obviously, the costs will be high for a
Journal of Coastal Research, Vol. 29, No. 5, 2013
1220 Jonkman et al.
system with a large defence length. A good example concerns
the protected areas that are found in the so-called Plaquemines
area in Louisiana, southeast of New Orleans. This is a large
area along the Mississippi with only about 25,000 inhabitants,
protected from river and hurricane flooding by approximately
185 km of levees (Van der Waart et al., 2010). This leads to a
ratio of 135 inhabitants per kilometre of levee, whereas the
typical ratio in most areas in the Netherlands is greater than
1000 inhabitants per kilometre of dike. Because of the large
system length, protecting the Plaquemines area will be
relatively costly. In cost-benefit studies, areas with a relatively
low economic value but high adaptation costs will have a lower
optimal protection level (or ‘‘ demand for safety’’) than an area
with a high concentration of economic values and a relatively
small defence length (see e.g. Eijgenraam, 2006; Penning-
Rowsell et al., 2003; Tol, 2006; Van Dantzig, 1956).
The length of a coastal flood defence system may be
shortened by closing off estuaries by means of dams or barriers.
This could bring additional advantages, such as flood risk
reduction and benefits for agriculture (availability of fresh
water). Barriers could also have negative effects on the
ecological system and on navigation. Such an adaptation is
usually done when the benefits (e.g. lower costs because of a
smaller system length and reduction of risk) outweigh the costs
of such a modification (e.g. additional dams or storm surge
One of the key questions concerning climate-induced sea-
level rise is how much costs of protection will increase with
changing conditions. The costs are influenced by two relation-
ships: the actual/expected increase of the hydraulic loads over
time (largely determined by the rate of sea-level rise) and the
costs for upgrading coastal defences to these loads.
The effect of the first factor is illustrated in Figure 8, which
schematically shows the periodic steps that would be required
to raise and strengthen coastal defences to account for sea-level
rise. Even when the unit costs of strengthening defences would
be constant, acceleration in the rate of sea-level rise would still
lead to a nonlinear increase of costs. It is noted that the
adaptations in Figure 8 follow the observed rise of sea level.
More proactive strategies for adaptation would anticipate the
sea-level rise. The relationship between sea-level rise and
adaptation of coastal defences is discussed further below.
Effects of Sea-Level Rise on Coastal Defences—
Example and Discussion
The costs of adaptation of the coastal defences as a function of
sea-level rise will be to a large extent be determined by the
physical changes that will have to be made to the sea defences.
To gain insight into these changes, one should consider key
design parameters (height, width, and cross-sectional area)
and how they change with sea-level rise. Figure 9 schemati-
cally shows the effects of different amounts of raising and
widening for a typical sea dike cross section in The Nether-
lands. Table 6 summarises the changes in dimensions as a
function of sea-level rise.
Investigating the relationship between the key dike design
parameters and sea-level rise requires several assumptions.
First, it is assumed we deal with a flood defence that just fulfils
its design requirements with respect to, for example, overtop-
ping (e.g.a10
/m per second allowable overtopping
discharge). Hence, any increase in boundary condition (design
water level, wave height) translates to an increase in required
dike dimensions. Second, we assume the waves are depth-
limited, which is often the case in front of Dutch flood defences.
The required dike heightening (DH
) due to sea-level rise is
calculated by Equation (1),
¼ DH
design WL
þ DH
wave run-up
where DH
design WL
is the increase in design water level, which is
equal to the increase in sea-level rise (DSLR), and D H
wave run-up
is the increase in wave run-up. DH
wave run-up
can be calculated
by Equation (2),
wave run-up
¼ 8 3 DH
3 DSLR tanðaÞð2Þ
where DH
is the increase in significant wave height and tan(a)
is the outer slope angle. For depth-limited waves, DH
can be
approximated by the breaker parameters (c
increase in water level, DSLR. If we assume a slope of 1 : 4
and a breaker parameter of 0.5, the increase in wave run-up
equals DH
wave run-up
¼ DSLR, and the outcome of Equation (1)
becomes DH
¼ 2DSLR.
The breaker parameter, slope, and breaker types influence
(mostly linearly) the DH
wave run-up
, requiring other formulas
and resulting in other outcomes of Equation (2). However, the
chosen wave run-up equation and parameters (which are
representative for an average Dutch sea dike) give a good, yet
possibly slightly conservative, estimate, which is detailed
enough considering the scope of the paper. Other main design
parameters (width, cross-sectional area) follow directly from
the dike height following geometrical relations because other
failure modes (e.g. slope instability) are not considered to be
dominant with this dike set-up. If waves are not depth-limited,
the local bathymetry and wave climate determine the required
adaption of the flood defence. If the wave climate remains
constant, the increased water level results in increased
overtopping and extra required design height DH
The relative changes in dike parameters have been plotted as
a function of a 0–2-m sea-level rise in Figure 10. This embraces
the likely range of climate-induced rise in sea level during the
Figure 8. The effects of the rate of sea-level rise on periodic dike raising.
Left: Linear sea-level rise: the height or periodic raising remains constant.
Right: Exponential sea-level rise: the height of periodic raising increases
over time.
Journal of Coastal Research, Vol. 29, No. 5, 2013
Costs of Adaptation to Sea-Level Rise 1221
21st Century (Nicholls et al., 2011). The height and width of the
sea dike show a linear increase with sea-level rise. Although
there is a small nonlinear effect, the increase in cross-sectional
surface can be approximated very well by a linear trend line (R
¼ 0.997). Even for a 5-m sea-level rise, the linear trend still has
an excellent fit (R
¼ 0.989). On the basis of these results, a
linear relationship is expected between the sea-level rise and
the cross-sectional area for the typical dimensions of an
existing sea dike and expected ranges of sea-level rise in the
coming centuries (0.5–5 m). A stronger quadratic effect will be
found for higher sea-level rise rates or situations in which a
new coastal sea dike has to be built from scratch.
This example shows that the height, width, and cross section
of a typical existing sea dike in the Dutch situation are expected
to increase linearly with sea-level rise. If material prices
remain constant in time, that would imply that this important
determinant of the unit cost prices for the dike construction
itself will not change over time.
However, several other factors could influence the develop-
ment of costs over time and contribute to a nonlinear (concave)
increase of costs. The wider the footprint of the dike, the more
likely that houses or other buildings or objects will have to be
removed or that more costly measures will have to be
implemented to prevent this. Other developments could affect
unit cost price levels, such as changes in labour and material
costs, changes in the regional and global construction markets,
or the development of new construction techniques with lower
Table 6. Effects of sea-level rise on changes in height, width, and cross
section for a typical Dutch sea dike.
Rise (m)
D Height
D Width,
D Cross Section,
0 basis ¼ 10m basis ¼ 80m basis ¼ 425m
0.5 1 (10) 7 (9) 81 (19)
1 2 (20) 14 (18) 169 (40)
2 4 (40) 28 (35) 366 (86)
5 10 (100) 70 (88) 1125 (265)
It is assumed that wave breaking is depth limited. An increase in the sea
level leads to an increase in the wave height and wave run-up, so that the
required raising is larger than the sea-level rise.
Figure 10. Relative increase in height, width, and cross section as a function
of sea-level rise for a typical Dutch coastal dike, scaled for the current
Figure 9. Effects of sea-level rise on the required sea dike cross section. Sea-level rise values in meters are shown in the dike cross sections.
Journal of Coastal Research, Vol. 29, No. 5, 2013
1222 Jonkman et al.
prices. Additionally, changes in the coastal defence system
could affect the internal water management system, especially
in low-lying delta areas. For example, if higher coastal dikes
are built as a response to sea-level rise, pumps with higher
capacities will be needed to drain the low-lying areas behind
the coastal defences. It depends on local circumstances which
parameters and processes are dominant; thus, it depends on
local circumstances whether the costs will develop linearly or
So far, we have assumed that the standard of protection of
remains constant so that the coastal defence dimensions
‘‘ follow’’ sea level. However, because many coastal regions
are characterized by economic and population growth, these
developments could lead to a higher demand for safety in
coastal areas, which could lead to faster and larger changes in
the coastal defence system than expected because of sea-level
rise alone.
A study by Kok et al. (2008), as part of a nationwide study on
long-term adaptation in The Netherlands (Delta Committee,
2008), analysed the above effects in estimating the long-term
development of costs for flood protection as a function of sea-
level rise. It was found that the annual costs for adaptation of
river and coastal dikes were expected to remain constant over
the coming 50–100 years. However, the replacement of existing
major flood defence infrastructures, such as storm surge
barriers, was expected to lead to small stepwise increases in
these costs. The total costs for adaptation and maintenance
were presented as annual costs and these were, depending on
the rate of sea-level rise, between ME600 and BE1 per year,
which is about 0.1%–0.2% of the current GDP of The Nether-
lands. It was concluded that the protection of the country by
means of flood defences would be feasible and affordable in the
coming decades, even under worst-case sea-level rise scenarios
(Delta Committee, 2008; Kok et al., 2008).
This article provides new insights into cost estimates for
coastal defences that are especially relevant in low-lying delta
areas, but findings can also be applied more generically in
coastal areas where similar defence measures are used.
On the basis of actual project data, improved unit cost
estimates for coastal defences have been presented. For coastal
dikes in rural areas, these are significantly higher than those
from previous studies (Hoozemans, Marchand, and Penne-
kamp, 1993; IPCC CZMS, 1990). These results reinforce the
conclusion that these earlier unit costs only provide indicative
cost estimates and that their empirical basis is limited. Because
these previous studies from the 1990s are still a main input for
global vulnerability assessments of parameters such as coastal
adaptation costs, the numbers in these global studies need to be
reviewed and improved as appropriate. It is recommended that
the unit cost estimates that are used in future global studies
are based on actual project data for coastal defence projects
wherever possible. The data presented in this study are mainly
representative for low-lying delta areas where flood defences
are used. The presented information could be a starting point
for updating unit costs used in global studies, as it is found that
the available amount of data on costs for some important
coastal protection measures, such as dikes, floodwalls, and
storm surge barriers is limited. It was also shown that there is a
need to update the country factors used in the IPCC CZMS
(1990) study to obtain better regional cost estimates.
Analysis of the data revealed considerable variability in unit
cost estimates, even for one region for a single type of coastal
defence measure. Rather than presenting point estimates, it is
recommended to present and analyse unit cost estimates by
means of appropriate bandwidths and sensitivity analysis (cf.
Nicholls, Tol, and Vafeidis, 2008).
It is important to take into account the factors that will
influence the cost estimates in determination of adaptation
costs and the demand for safety. Relevant characteristics that
would ideally be taken into account in regional and global
studies include the length of the coastal defence system, the
coastal defence features, and the associated unit costs. Further
implementation of these elements in coastal vulnerability
assessment models, such as the DIVA model (Vafeidis et al.,
2008), is recommended. A good approximate measure for the
optimal protection level proves to be the number of inhabitants
per unit length of the defence (Eijgenraam, 2006). Investiga-
tion into how this measure can be implemented in regional and
global vulnerability assessments is recommended.
Finally, the analysis for the example of a Dutch sea dike with
depth-limited wave breaking showed that important elements
in the cost estimates—width, height, and material quantities
will increase linearly for the range of sea-level rise rates that
are expected in the coming century. Other factors, such as
increasing costs for implementation of wider coastal defences in
an urban environment, adaptation of other (water) infrastruc-
tures, and future changes in materials and labour costs, could
contribute to a nonlinear (concave) increase of costs. Further
investigation into the relevance of such variables is recom-
mended based on actual local case studies.
The new project-based data provide insight into unit costs of
both various hard (dikes, floodwalls) and soft (wetlands and
nourishments) measures. These soft solutions with ecological
benefits can play an important role in adapting vulnerable
coastlines (Jones, Hole, and Zavaleta, 2012; Van Slobbe et al.,
2012). With increasing populations and economic value and
higher demands for safety, it is important to evaluate
thoroughly the level of flood risk reduction achieved by various
categories of measures (Jongejan et al., 2008). However, it is
important that unit costs, as presented in this study, are
compared fairly, which is not always straightforward, as is
illustrated in the publication by Jones, Hole, and Zavaleta
(2012). These authors compare the unit costs of 1 km of dike
from Hillen et al. (2010)—also presented in this study—with
the costs of 1 ha of mangrove in Vietnam (Jones, Hole, and
Zavaleta 2012, pg. 507). However, these two measures cannot
be compared directly because they do not relate to similar levels
of risk reduction. During Hurricane Rita, a surge reduction due
to wetlands was found in western Louisiana with a typical
figure of 1 m of surge reduction per 11–19 km (Resio and
Westerink, 2008). Hence, a fair cost comparison for this specific
case is likely to be a 1-m dike raise along 1 km of existing dike
stretch with the maintenance and build-up of 10–20 km
wetlands in front of the existing dike. Also, the effectiveness of
soft and hard solutions have to be compared and evaluated on a
Journal of Coastal Research, Vol. 29, No. 5, 2013
Costs of Adaptation to Sea-Level Rise 1223
case-by-case basis. For the case of Louisiana, Resio and
Westerink (2008) indicate how inland marshes can attenuate
storm surges for certain storm tracks but also that wetlands
could increase storm surge levels for other regions and storm
conditions. It is expected that ‘‘ hard defences’’ will remain an
important element of the overall strategy of coastal adaptation
and flood management, especially for effective adaptation of
densely populated areas to the effects of climate change and
higher demands for safety. Therefore, a promising research
and development direction is to look for ways to integrate
ecological and engineering design perspectives and hard and
soft measures. The costs and benefits of these types of solutions
will have to be assessed in future studies on the adaptation of
coastal systems.
This research was funded by the U.K. Department for
Energy and Climate Change (DECC)/Department for Envi-
ronment, Food, and Rural Affairs (Defra) through the AVOID
programme on avoiding dangerous climate change. This
project was supported by the National Science Foundation
(NSF) under EFGRI grant 0836047. Any opinions, findings,
and conclusions or recommendations expressed in this
material are those of the authors and do not necessarily
reflect the views of the NSF. The contributions of Marli
Geldenhuys, Ries Kluskens, M. Kok, J.K. Vrijling, and M.J.F.
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Unit cost estimates for New Orleans coastal defence projects.
Project Project Code Polder
($ 3 10
Unit Costs per
Unit Length
Range of Costs
per Unit Length
per Unit Raising
E/[m km])
Earthen levee raise (eight projects) 1.1–2.5 2.5–5
Orleans Village to Hwy 45, Levee—
Phase 1
WBV-14b.1 Westbank 3.0 14.0 2.2
Westbank IHNC—Almonaster to
Lakefront Floodwall
LPV-120.01 Orleans Metro 1.2 4.6 1.8
Reach 3 Lakefront Levee (3rd Lift) LPV-02.1 Jefferson 2.3 9.1 1.8
Reach 1 Lakefront Levee LPV-00.1 Jefferson 2.0 7.8 1.8
Orleans Village to Hwy 45, Levee WBV-14b.1 Harvey / Westwego 3.0 14.0 2.2
Hero Canal Reach 1, 2nd Enlgt WBV-12 Belle Chase 2.2 11.8 2.5
Raise Levee—Paris Rd. to South
LPV-108 New Orleans East 6.3 15.5 1.1
Citrus Back Levee—Michoud Canal
to Michoud Slip to Auth. Elevation
LPV-113 New Orleans East 1.5 6.7 2.0
Construction of new floodwall (five
17.8–40.8 4.9–11.8
Chalmette Loop Levee—Bayou
Bienvenue to Bayou Dupre
LPV-145 St Bernard 5.7 408.0 32.7
Journal of Coastal Research, Vol. 29, No. 5, 2013
Costs of Adaptation to Sea-Level Rise 1225
APPENDIX. Continued.
Project Project Code Polder
($ 3 10
Unit Costs per
Unit Length
Range of Costs
per Unit Length
per Unit Raising
E/[m km])
Chalmette Loop Levee—Hwy 46 to
River (Verret to Caernarvon)
LPV-148.02 St Bernard 8.2 317.0 17.8
Contract 1, Sectorgate to Boomtown
WBV-01 Gretna / Algiers 1.5 132.0 40.8
Chalmette Loop Levee—Bayou Dupre
to Hwy 46 Floodwall
LPV-146 St Bernard 7.6 452.0 27.5
New Orleans East Back Levee—CSX
RR to Michoud Canal
LPV-111.01 New Orleans East 5.3 403.0 35.0
Combination of floodwall and levee
raise and strengthening (four
4.4–9.2 n.a.
West Return Floodwall (Southern
Segment)—Phase 2
LPV-03.2A Jefferson 3.3 36.9 5.1
T-Wall Existing Alignment-
Lakefront Airport—East
LPV-105.02 New Orleans East 1.3 19.5 6.7
Reach 4 Lakefront Levee—Phase 2 LPV-19.2 Orleans Metro 0.3 2.6 4.4
Station 160þ00 to Hwy 90 WBV-17b.1 Harvey / Westwego 1.0 19.9 9.2
Source: USACE, 2009.
Based on uncertain and variable estimates of raising of levees and floodwall elevations. Based on the project information, the levees are expected to be
raised 0.4–0.5 m in most projects. The height of the concrete floodwalls was approximately 12 ft (3.6 m). No information was available on the height of raising
for the ‘‘ combination of floodwall and levee raise’’ projects.
Journal of Coastal Research, Vol. 29, No. 5, 2013
1226 Jonkman et al.
... In this research, the width of vegetation and packing density are considered to be the key parameters in mitigating overtopping discharge. A Crown wall with parapets is one of the retrofitting methods for dikes and berms, and the capacity of the crown walls to mitigate the overtopping volume was compared for various heights and by increasing berm width [9,10,11]. Past literature [19,21,24] indicates that having tandem structures may also help protect the existing coastal structure from increased loading triggered due to climate change. The performance of submerged breakwater placed tandem to existing damage as a protection measure was studied for increased wave action due to climate change is presented in [21]. ...
... A typical Dutch Dike of scale 1:20 [11] was considered in this study and a total of 128 small-scale experiments were conducted in wave flume of Hydraulic Laboratory of the University of Bologna (Unibo). The schematic diagram of the dike considered in the study [11, is as shown in Fig.6 (not to scale). ...
... Score q * = -Red q * . 100 (11) Score F * = -Red F * . 100 (12) Score (∆cost)= -0.48. ...
Conference Paper
As climate change is widespread, rapid, and intensifying, as reported by Intergovernmental Panel on Climate Change, coastal areas are expected to witness a continued increase in sea level throughout the twenty-first century and the future. Further, the intensity and frequency of extreme events are expected to increase in the future. These alarming climate change trends deem immediate engineering intervention to protect the coastline around the world. Coastal defense structures are crucial components in protecting coastal communities and defense-related infrastructures. The existing coastal structures may not be functional to the desired level or become less functional in the future due to climate change and sea-level rise impacts, this might lead to an increase in the wave-induced loads and increased wave overtopping rates resulting in coastal flooding and inundation. Therefore, it is essential to develop methodologies to upgrade and reinforce the coastal structures, thereby making them climate-resilient. There are few efforts taken in the past in this direction, and the present study is aimed to deepen the understanding of the performance of various retrofitting structures in enhancing the resilience against increased wave action. In the present study, we focus on a review of various up-gradation approaches used by various researchers over a wide variety of coastal structures to tackle the climate change impacts and discuss their performance in enhancing coastal resilience. Also, we discussed a new methodology for finding the optimal solution among various alternative methods with an example. This study will help to understand the knowledge gap involved in the existing literature and determine the future research direction towards climate-resilient coastal structures.
... Potential adaptation strategies in coastal areas include beach nourishment, ecosystem restoration, hard structures, retreat, zoning and building codes (Hinkel et al., 2012;Gopalakrishnan et al., 2016;Jonkman et al., 2013). The adaptation options that aim to provide coastal protection can be separated into engineering and nature-based solutions. ...
Full-text available
Environmental change poses an enormous threat, especially in low and middle income countries (LMICs). In this context, nature-based solutions (NBS) are increasingly gaining interest. However, NBS face a number of barriers, of which the challenge of obtaining sufficient financial resources is a major one. To guide investments towards NBS, there is a demand for economic analyses on the welfare effects of NBS. Since many NBS benefits are non-market by nature, stated preference (SP) studies serve as the most suitable valuation method to value NBS benefits. In SP studies, respondents are asked to make trade-offs between positive changes in ecosystem services and a payment. This payment is necessary for the calculation of willingness to pay (WTP) and is usually monetary, which may complicate trade-offs in LMICs due to generally lower income levels. In response to this, SP studies in LMICs increasingly employ time payments, which seem like a suitable alternative, but challenges and questions related to the use of time payments remain. The aim of this dissertation is to support the decision-making on the implementation and financing of NBS in LMICs. Therefore, we focus on how we can better capture the values of ecosystem services in lower income contexts by investigating methodological challenges related to the use of time payments and by applying time-based values in economic and financing analyses. We do so via discrete choice experiments (DCE) with both time and money payments that were implemented in four sites across rural and urban Ghana and Vietnam. In Chapter 2 we investigate how to convert time to monetary values based on the Vietnam case studies. In this chapter we advance on current conversion practices by applying six different conversion rates, including generic and individual-specific rates as well as wage and leisure rates. We identify that WTP estimates based on the time payments are substantially higher. Furthermore, we identify that time-based WTP estimates differ significantly across the different conversion rates. In Chapter 3 we continue to work on the time-to-money conversion rate, in this case based on the Ghanaian case studies. In this chapter we trial a non-wage-based conversion rate, an average market wage value, and an average sample-based earnings value. We test the underlying implicit assumptions related to the use of an average (market) wage value or leisure rate, which we refute. WTP estimates are again substantially higher when based on the time payments. In this chapter we furthermore also identify that market integration levels may allow for the convergence of WTP estimates from the different payment types. In Chapter 4 we conduct a cost-benefit analysis (CBA) of both a nature-based and an engineering solution to coastal erosion in the rural Ghanaian study site. In this CBA, we calculate the benefits of erosion prevention either by using the money-based or time-based WTP estimates. We find overall negative welfare effects for both solutions when money payments are applied, but positive welfare effects when time payments are applied. In Chapter 5 we focus on an alternative application of the time-based values, namely as a source of NBS financing. The results indicate that time contributions from households for the implementation and maintenance of NBS, which are often labour intensive, are motivated by social capital and coping appraisal. Furthermore, based on examples of the Vietnamese case studies we calculate that time contributions could cover 29% and 44% of the financial needs of the specified NBS. Based on the results presented in this dissertation we provide recommendations to research, practice and policy as well as suggestions for future research within and beyond the research focus of this dissertation.
... We considered two kind of works: levees in the most critical zones of the hydraulic network, and the creation of flood expansion areas ruled by weirs. In order to estimate the costs of raising the banks, reference is made to the study conducted by [46], which estimate between 4.5-12.4 million Euros per km of length and per meter of raising the embankment in rural areas. In the present study a unit cost of C = 4.5 million Euros/km per meter of embankment elevation will be considered. ...
Full-text available
Coastal areas are particularly vulnerable to flooding from heavy rainfall, sea storm surge, or a combination of the two. Recent studies project higher intensity and frequency of heavy rains, and progressive sea level rise continuing over the next decades. Pre-emptive and optimal flood defense policies that adaptively address climate change are needed. However, future climate projections have significant uncertainty due to multiple factors: (a) future CO2 emission scenarios; (b) uncertainties in climate modelling; (c) discount factor changes due to market fluctuations; (d) uncertain migration and population growth dynamics. Here, a methodology is proposed to identify the optimal design and timing of flood defense structures in which uncertainties in 21st century climate projections are explicitly considered probabilistically. A multi-objective optimization model is developed to minimize both the cost of the flood defence infrastructure system and the flooding hydraulic risk expressed by Expected Annual Damage (EAD). The decision variables of the multi-objective optimization problem are the size of defence system and the timing of implementation. The model accounts for the joint probability density functions of extreme rainfall, storm surge and sea level rise, as well as the damages, which are determined dynamically by the defence system state considering the probability and consequences of system failure, using a water depth–damage curve related to the land use (Corine Land Cover); water depth due to flooding are calculated by hydraulic model. A new dominant sorting genetic algorithm (NSGAII) is used to solve the multi-objective problem optimization. A case study is presented for the Pontina Plain (Lazio Italy), a coastal region, originally a swamp reclaimed about a hundred years ago, that is rich in urban centers and farms. A set of optimal adaptation policies, quantifying size and timing of flood defence constructions for different climate scenarios and belonging to the Pareto curve obtained by the NSGAII are identified for such a case study to mitigate the risk of flooding and to aid decision makers.
... For the land barrier, the dike alternative was considered. Unit costs from previous projects ( Jonkman, Hillen, Nicholls, Kanning, & van Ledden, 2013) and a more material volume-based approach were considered. Both resulted in a cost estimate of the construction of a coastal dike of about 45 M$ per kilometer. ...
Full-text available
My research goal for the PIRE program was to understand and quantify the flood risk to above ground storage tanks (AST) in the Port of Rotterdam since consequences of AST failure can be catastrophic for the surrounding environment and communities, and the economy. Furthermore, I also wanted to understand the flood risk mitigation approach adopted in the Netherlands to gain insights on how AST flood risk can be managed in the Netherlands. For hurricane risk assessment of ASTs, I used physics-based fragility to estimate the vulnerability of ASTs subjected to inundation depths corresponding to different return periods. The NSF PIRE program components such as meetings with experts and stakeholders helped me understand the flood risk management philosophy in the Netherlands. Site visits and other interactions with experts and students from various disciplines also helped me broaden my perspective on flood risk management using a holistic multidisciplinary approach.
... Current flood protection systems are under pressure due to climate change, in the form of more intense and frequent storms, heavier rainfalls, and accelerated sea level rise (Oppenheimer et al., 2019). Dikes will need to be made higher and stronger to keep up with changing climate, which will lead to increasing costs (Jonkman et al., 2013). Because of this, the interest in more costeffective solutions has grown in recent years for both coasts and rivers. ...
Full-text available
The last years, capacity of vegetation to reduce wave impact is receiving considerable attention. To predict wave attenuation processes within vegetation fields reliable estimates of vegetation parameters are needed. This proves to be difficult for woody vegetation as it consists of complex branch structures, characterized by varying branch densities, diameters and angles. State of the art physical and numerical models effectively use a single value for the diameter, bv and density, N of vegetation, which is unrepresentative for complex vegetation, such as trees. Trees can be better described by the projected frontal-surface area, Av. Hence, this work compares methods to quantify the Av in space for a pollard willow forest, and determines suitability of these methods for predicting wave attenuation using a spectral wave model (SWAN). We use data from manual measurements and Terrestrial Laser Scans (TLS), to estimate the vertical distribution of Av; and data from large-scale flume experiments performed on a willow forest to verify model sensitivity to Av inferences. As a baseline for comparison, tree models that describe the structure of the trees in various degrees of complexity are compiled. The most realistic tree model is used to quantify potential errors in TLS and basic manual measurements of N and bv. An initial comparison shows that the TLS data underestimates Av, which indicates that conducting manual measurements is more suitable to quantify a homogeneous forest. We found that the TLS suffers from shadowing effects (i.e., blockage of laser beams) and we recommend to apply a correction factor to improve its measurements. Furthermore, we identified the impact that the different methods to determine Av have on the estimation of wave attenuation using SWAN; in addition we verified the model results with data from large-scale flume experiments performed on the willow forest. The modeled sensitivity tests indicate large differences in wave attenuation and, consequently, a wide range (0.94–1.70) of bulk drag coefficients, C˜D , for the various methods applied. This shows the variation of outcome between measuring methods and highlights the importance of stating the selected method for reliable frontal-surface area estimations, and consequently for reliable wave attenuation predictions.
... impermeable revetments and seawalls) is set to be £ 64.2 million, which is an indicative cost for upgrading 15km-long coastal defence up to 3.5 mAOD level (NFDC 2010). The estimation of the costs for different heightening follows a linear relation between height and cost by the previous study (Jonkman et al. 2013) and this distribution rule (Eqs. (4) and (5)) is applied for each stage adaptation. ...
Full-text available
Climate change adaptation inherently entails investment decision-making under the high levels of uncertainty. To address this issue, a single fixed large investment can be divided into two or more sequential investments. This reduces the initial investment cost and adds flexibility about the size and timing of subsequent investment decisions. This flexibility enables future investment decisions to be made when further information about the magnitude of climate change becomes available. This paper presents a real option analysis framework to evaluate adaptations including flexibility to reduce both the risk and uncertainty of climate change, against increasing coastal flooding due to sea-level rise as an example. The paper considers (i) how to design the sequence of adaptation options under growing risk of sea-level rise, and (ii) how to make the efficient use of flexibility included in adaptations for addressing uncertainty. A set of flexibilities (i.e. wait or future growth) are incorporated into single-stage investments (i.e. raising coastal defence from 2.5 mAOD to 3.5mAOD or 4.0 mAOD) in stages so that multiple-stage adaptations with different heights are created. The proposed method compares these sequentially growing adaptations in economic terms, including optimisation, providing additional information on the efficiency of flexible adaptation strategies given the uncertainty of climate change. The results from the evaluation enable decision-makers to identify long-lasting robust adaptation against the uncertainty of climate change.
Investments in disaster risk reduction not only reduce damage, but also promote social and economic development. While there are many methods of evaluating investments in disaster risk reduction, most methods are based on losses and benefits to the entire region, and the differences in the benefits for different social classes are unclear. Therefore, it is difficult to ascertain the impact on the poor, who are particularly severely affected by disasters. Here, we present a method for assessing the impact of disaster risk reduction investments on the poor based on case study data from Bago, Myanmar, including interviews with 440 households. The results show that by considering the development of the poor, the benefits of investment in disaster risk reduction can increase by ∼4.4 times. Although there is uncertainty in modeling such a complex system, the results demonstrate the need to consider both the direct and indirect impacts of disaster risk reduction investments, for facilitating sustainable development in developing countries.
Many coastal areas around the world are densely populated and at risk from flooding, but utilize different strategies to deal with coastal hazard. This chapter summarizes how Dutch concepts for coastal flood risk reduction have been explored for Galveston Bay. Firstly, it is shown how risk-based screening methods can help to evaluate various alternative strategies based on metrics such as costs, risk reduction and (societal and environmental) impacts. Application of this approach for Galveston Bay that a coastal spine alternative would entail a large investment, but it would provide the greatest risk reduction by maximizing the protected area. Secondly, a preliminary design for the coastal spine (also known as the Ike Dike) has been elaborated for protection of the region against storm surges, with involvement of Dutch and international students and experts. It includes storm surge barriers at Bolivar Roads and San Luis Pass, and several alternatives for the land barrier—including a fortified dune. Important aspects for future work are discussed, such as the cost estimation, in-bay measures, and the need for integral and proactive planning.
Technical Report
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Ore-sand: A potential new solution to the mine tailings and global sand sustainability crises-Final Report.
Conference Paper
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This paper aims at risk analysis and the investigation of safety aspects of coastal flood defences in Vietnam. The sea dike system has been actually designed by a 20 to 25 years return period. From the current situation it seems that the dike system is not sufficient to withstand the actual sea boundary conditions. Accurate safety assessment of the existing coastal defence system is of large importance. It can quantify the possible consequences after failure of the defensive system, the loss of life, economic, environmental, cultural losses and further intangibles. To determine if safe is safe enough, an investigation is carried out in this paper to determine other types of risks to which the local population is exposed, apart from the flood risk. The issues addressed in this paper may support long-term planning and decision-making for rehabilitation of the coastal flood defences in Vietnam.
Technical Report
Full-text available
A large and fast-growing part of the world’s population lives in low-lying coastal zones. To sustain economic activities and living in these areas a wide range of coastal defence measures has been constructed. These coastal defence measures reduce the risk to economic values and populations in coastal zones prone to flooding. Coastal defence measures can even help to enable living in areas that are below sea level, for example in parts of the Netherlands and New Orleans. Climate change, and more specifically sea level rise, poses a direct threat to these areas (Ericson et al., 2006; Nicholls et al., 2008). Sea level rise requires the coastal defence measures to be adapted to higher water levels and more intense hydraulic boundary conditions (such as waves and storm surges). The exposure of coastal zones and especially coastal cities to flooding was determined by Nicholls et al. (2008). However the risk of flooding and the costs of adaptation to sea level rise are greatly influenced by coastal defence measures. The study of Linham et al. (2010) builds upon Nicholls et al. (2008) to determine the risk and impact of flooding in port cities. This study is part of a global study on the costs of adaptation to the effects of climate change (Linham et al., 2010). It adds information from three specific case studies (the Netherland, New Orleans and Vietnam) to the global study. The case study areas are comparable by type of coast; all are low-lying deltaic coastal areas. This study investigates the unit cost estimates of coastal defence for the full range of hard and soft engineering measures, such as dikes/levees, sea walls, (beach) nourishments and other measures, for example storm surge barriers.
Conference Paper
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The recent flooding and devastation of the greater New Orleans region during hurricane Katrina represented the most costly peace-time failure of an engineered system in North American history. Extensive investigations and analyses have been performed by several major teams in the wake of this disaster, and some very important lessons have been learned. Many of these have very direct and urgent applications to levee systems in other regions throughout the U.S., and the world. Lessons include the importance of proper evaluation of risk and hazard; so that appropriate decisions can be made regarding the levels of expense and effort that should be directed towards prevention of catastrophe, and the levels of post-disaster response capability that should be maintained as well. The making of appropriate decisions, given this information regarding risk levels, is then also important. Also of vital importance are numerous "engineering" lessons regarding analysis, design, construction and maintenance; hard-won lessons with applications to flood protection systems everywhere. We must now do everything possible to capitalize upon these; and to prevent a recurrence of this type of catastrophe in the future..
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This paper presents a first estimate of the exposure of the world's large port cities (population exceeding one million inhabitants in 2005) to coastal flooding due to sea-level rise and storm surge now and in the 2070s, taking into account scenarios of socioeconomic and climate changes. The analysis suggests that about 40 million people (0.6% of the global population or roughly 1 in 10 of the total port city population in the cities considered) are currently exposed to a 1 in 100 year coastal flood event. For assets, the total value exposed in 2005 across all cities considered is estimated to be US$3,000 billion; corresponding to around 5% of global GDP in 2005 (both measured in international USD) with USA, Japan and the Netherlands being Climatic Change (2011) 104:89–111 the countries with the highest values. By the 2070s, total population exposed could grow more than threefold due to the combined effects of sea-level rise, subsidence, population growth and urbanisation with asset exposure increasing to more than ten times current levels or approximately 9% of projected global GDP in this period. On the global-scale, population growth, socioeconomic growth and urbanization are the most important drivers of the overall increase in exposure particularly in developing countries, as low-lying areas are urbanized. Climate change and subsidence can significantly exacerbate this increase in exposure. Exposure is concentrated in a few cities: collectively Asia dominates population exposure now and in the future and also dominates asset exposure by the 2070s. Importantly, even if the environmental or socioeconomic changes were smaller than assumed here the underlying trends would remain. This research shows the high potential benefits from risk-reduction planning and policies at the city scale to address the issues raised by the possible growth in exposure.
To improve the estimate of economic costs of future sea-level rise associated with global climate change, this report generalizes the sea-level rise cost function originally proposed by Fankhauser, and applies it to a new database on coastal vulnerability developed as part of the Dynamic Interactive Vulnerability Assessment (DIVA) tool. An analytic expression for the generalized sea-level rise cost function is obtained to explore the effect of various spatial distributions of capital and nonlinear sea-level rise scenarios. With its high spatial resolution, the DIVA database shows that capital is usually highly spatially concentrated along a nation’s coastline, and that previous studies, which assumed linear marginal capital loss for lack of this information, probably overestimated the fraction of a nation’s coastline to be protected and hence protection cost. In addition, the new function can treat a sea-level rise scenario that is nonlinear in time. As a nonlinear sea-level rise scenario causes more costs in the future than an equivalent linear sea-level rise scenario, using the new equation with a nonlinear scenario also reduces the estimated damage and protection fraction through discounting of the costs in later periods. Numerical calculations are performed, applying the cost function to the DIVA database and socioeconomic scenarios from the MIT Emissions Prediction and Policy Analysis (EPPA) model. The effect of capital concentration substantially decreases protection cost and capital loss compared with previous studies, but not wetland loss. The use of a nonlinear sea-level rise scenario further reduces the total cost because the cost is postponed into the future.
This paper presents the Climate Framework for Uncertainty, Negotiation and Distribution (FUND), an integrated assessment model of climate change, and discusses selected results. FUND is a nine-region model of the world economy and its interactions with climate, running in time steps of one year from 1990 to 2200. The model consists of scenarios for economy and population, which are perturbed by climate change and greenhouse gas emission reduction policy. Each region optimizes its net present welfare. Policy variables are energy and carbon efficiency improvement, and sequestering carbon dioxide in forests. It is found that reducing conventional air pollution is a major reason to abate carbon dioxide emissions. Climate change is an additional reason to abate emissions. Reducing and changing energy use is preferred as an option over sequestering carbon. Under non-cooperation, free riding as well as assurance behaviour is observed in the model. The scope for joint implementation is limited. Under cooperation, optimal emission abatement is (slightly) higher than under non-cooperation, but the global coalition is not self-enforcing while side payments are insufficient. Optimal emission control under non-cooperation is less than currently discussed under the Framework Convention on Climate Change, but higher than observed in practice.
Previous studies suggest that the expected global warming from the greenhouse effect could raise sea level 50 to 200cm in the next century. This article presents the first nationwide assessment of the primary impacts of such a rise on the US: the cost of protecting ocean resort communities by pumping sand onto beaches and gradually raising barrier islands in place; the cost of protecting developed areas along sheltered waters through the use of levees (dikes) and bulkheads; and the loss of coastal wetlands and undeveloped lowlands. The total cost for a 1m rise would be between $270 and $475 billion, ignoring future development. We estimate that if no measures are taken to hold back the sea, a 1m rise in sea level would inundate 30 000km2 with wet and dry land each accounting for about half the loss. The 1500km2 of densely developed coastal lowlands could be protected for approximately $1000 to $2000 per year for a typical coastal lot. Given high coastal property values, holding back the sea would probably be cost-effective. To ensure the long-term survival of coastal wetlands, federal and state environmental agencies should begin to lay the groundwork for a gradual abandonment of coastal lowlands as sea level rises. -from Authors