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Communications on Hydraulic and Geotechnical Engineering
2010-01
ISSN 0169-6548
Coastal defence cost estimates
Case study of the Netherlands, New Orleans and Vietnam
———————————— Report of measurements and observations —————————————
M.M. Hillen
S.N. Jonkman
W. Kanning
M.Kok
M.A. Geldenhuys
M.J.F. Stive
April 2010
Communications on Hydraulic and Geotechnical Engineering
2010-01
ISSN 0169-6548
The communications on Hydraulic an Geotechnical Engineering are published by the Department of
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This report has been produced by Delft University of Technology in cooperation with Royal
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© 2010 TU Delft, Department Hydraulic Engineering;
1
Coastal defence cost estimates
case study of the Netherlands, New Orleans and Vietnam
Delft University of Technology, in cooperation with Royal Haskoning
April 2010
M.M. Hillen MSc (Royal Haskoning), S.N. Jonkman PhD (DUT), W. Kanning MSc (DUT),
M. Kok PhD (DUT), M.A. Geldenhuys BSc (DUT-COMEM) and prof. M.J.F. Stive (DUT)
2
3
Table of contents
1
Background and objective .......................................................................................4
2
Case study areas.....................................................................................................6
2.1
The Netherlands ..............................................................................................6
2.1.1
Background, history .................................................................................6
2.1.2
Coastal defence measures.......................................................................9
2.1.3
Cost estimates .......................................................................................10
2.2
New Orleans (U.S.)........................................................................................15
2.2.1
Background, history ...............................................................................15
2.2.2
Coastal defence measures.....................................................................16
2.2.3
Cost estimates .......................................................................................17
2.3
Vietnam .........................................................................................................22
2.3.1
Background, history ...............................................................................22
2.3.2
Coastal defence measures.....................................................................24
2.3.3
Cost estimates .......................................................................................25
2.4
Storm surge barriers......................................................................................27
3
Coastal defense cost estimates and analysis ........................................................31
3.1
Unit cost prices for coastal defences..............................................................31
3.1.1
Overview................................................................................................31
3.1.2
Comparison with IPCC CZMS (1990).....................................................34
3.2
Overview of factors that determine the unit cost price....................................35
3.3
Cost estimates at a system level....................................................................37
3.4
Relationship between sea level rise and coastal defence costs .....................41
4
Optimal protection levels .......................................................................................46
4.1
Background and general approach ................................................................ 46
4.2
Case studies..................................................................................................48
4.2.1
Netherlands............................................................................................48
4.2.2
New Orleans ..........................................................................................49
4.2.3
Vietnam..................................................................................................51
4.3
Discussion and comparison with the DIVA model ..........................................52
5
Main findings and recommendations .....................................................................54
6
References............................................................................................................57
Appendix I – Coastal defence cost estimates Cape Town (South Africa).......................59
4
1 Background and objective
Background
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.
Objectives
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.
In considering the costs of coastal defence and adaptation to climate change different
scale levels can be recognized (see Figure 1-1). At the highest level of detail specific
information from actual projects and designs can be utilized. This requires detailed
insight in the actual design and as built status of coastal defence projects. By combining
information from individual projects, cost estimates can be provided for one enclosed
coastal defence system, e.g. a dike ring or polder in the Netherlands or New Orleans.
Cost estimates at a national level can be obtained by aggregating information from
different defence systems. For example, Kok et al. (2008) report estimates of the costs
of adaptation of the flood defences in the Netherlands to different levels of sea level rise.
This is done by combining assessments of the response of different sub systems and
dike rings to the sea level rise (see also section 2.1). Finally, estimates for different
systems and countries can be aggregated to cost estimates at a regional, continental or
even global level.
5
global
country
Coastal defence
system
project
Level of detail
Figure 1-1: Different levels of detail for coastal defence cost estimates
This study largely focuses on cost estimates at the project and system level, whereas
previous studies (e.g. IPCC CZMS, 1990; Hoozemans et al., 1993) provide global
estimates. The project and system based estimates can be used as input for the cost
estimates at higher levels. The coastal defence cost estimates in this study are derived
from several studies conducted by the authors for the case study areas considered.
In addition to the three case studies for the Netherlands, New Orleans and Vietnam,
another case study has been included in this research. M.A. Geldenhuys BSc studied
the unit cost prices of coastal defence measures for Cape Town (South Africa) and this
work was conducted as part of the COMEM MSc program at the Delft University of
Technology. The results are included in appendix I of this report and the main results
and unit cost prices are also included in the main report. This is an interesting
comparison, as the three case studies (the Netherlands, New Orleans, Vietnam) are low-
lying deltaic coasts, whereas the coast of Cape Town is more variable in terms of
elevation, protection and coastal management strategies.
Structure of this report
This report is structured as follows. Section 2 provides a summary of relevant
information for the three case studies. A summary of the coastal defence cost estimates
is given in section 3. This section also includes a discussion of relevant aspects, such as
the relationship between the sea level rise rate and the unit cost prices. Section 4
reviews various studies for the three case studies that give insight in the optimal
standard of protection. The most important conclusions and recommendations are given
in section 5.
6
2 Case study areas
This study focuses on three study areas: the Netherlands, the city of New Orleans
(United States) and Vietnam (Figure 2-1). These three areas are all subjected to the risk
of coastal flooding. The case study areas have a similar type of coast, a low-lying deltaic
coast, and are all affected by sea-level rise.
This chapter gives a brief introduction of each case study area. The history, geography
and coastal defence measures of the area concerned are described. Furthermore the
studies as conducted by Delft University of Technology are introduced and the main
relevant literature is discussed. For each case study area the cost information on coastal
defence measures is provided and unit cost prices are derived.
Next to the overview of coastal defence measures and the main characteristics of the
case study area, the background of the cost data is given. This provides insight in the
background of the quantitative data and how to interpret these results.
Chapter 2.1 describes the Netherlands, in chapter 2.2 the New Orleans case study is
described and chapter 2.3 concerns the case study of Vietnam.
Costs are provided in euro (
), where US$ were used in studies a conversion rate of 1
= 1.35 US$ was applied.
Figure 2-1: World map with case study areas
2.1 The Netherlands
2.1.1 Background, history
The Netherlands, situated in the North-West of Europe, is a low-lying coastal zone of
which the Southern coastline is largely formed by a delta of three European rivers; the
7
Rhine, Meuse and Scheldt. About one-forth of the country is below sea level and half of
the country is situated below less than one meter above mean sea level. In the current
situation 65% of the Netherlands is prone to flooding (this includes river-flooding).
The history, existence and the present day landscape of the Netherlands has been
primarily influenced by water. Flooding events have shaped the Dutch landscape and
efficient water management has shaped the country’s organization: the water boards are
the oldest democratic organization in the Netherlands (13
th
century). Through land
reclamation by polders, a combination dikes and drainage, the Netherlands was shaped,
continuously balancing natural processes and human needs. More in general, the polder
concept as applied in the Netherlands can be considered a way to live in a delta; it is the
result of a continuous optimization to live and cultivate the land on the one hand and
sustain economic activities by controlling the water on the other.
In the current situation a flood defence system is in place to protect most of the
Netherlands from flooding. This systems consists of several flood defence measures;
dikes, storm surge barriers and several management systems such as dike rings and
beach nourishments. Large well-known coastal defence structures in the Netherlands
are the Afsluitdijk (direct translation: ‘Closure dike’) which closed off the tides of
Zuiderzee (former sea, adjacent to the Wadden Sea) and the Deltaworks, an extensive
system of dikes and storm surge barriers which protects the South-Western delta after
the catastrophic flooding of 1953. The strategy to dam rivers and close off estuaries
which shortens the coast line and the length of flood defences (Figure 2-2) has been
regarded an effective coastal defence strategy. Nowadays the Dutch flood defences
have safety standards up to 1/10000 years (Figure 2-3); e.g. these defence measures
can withstand a flooding event with a 1/10000 year frequency.
8
Figure 2-2: Shortening of the coastline of the Netherlands over time (Kok et al., 2008).
Figure 2-3: Dike-ring areas and their corresponding safety standards in the Netherlands
9
2.1.2 Coastal defence measures
As mentioned above, the coastal defence system of the Netherlands consists of several
coastal defence measures. The dike ring areas along the coasts have two different
safety standards (1/4000 and 1/10000) and are closed systems consisting of dunes, sea
dikes and storm surge barriers on the sea side. In addition to these coastal defence
measures, beach nourishments are applied along the Dutch coastline, which help to
sustain the sandy beaches and dunes (Figure 2-6).
Figure 2-4: Examples of sea dikes in the Netherlands (photos: Royal Haskoning)
Figure 2-5: Cross-section of a typical sea dike
10
Figure 2-6: Beach nourishment in the Netherlands (www.rijkswaterstaat.nl)
2.1.3 Cost estimates
For the Deltacommittee Kok et al. (2008) investigated the sustainability and financial
durability of the Dutch polder concept. The technical feasibility of the polder concept was
investigated; e.g. is it possible to maintain the polder approach with climate change by
keeping the current system of water defences in place? Also alternative strategies and
other measures where researched: reduction of flooding impact, alternative
enhancements of the flood defences and a different approach for the polder concept.
The costs to maintain the current safety standards with sea level rise and the costs to
adopt higher safety standards with sea level rise up to 2200 were investigated for the
primary water defences of the Netherlands. The costs mainly concern raising dikes,
construction of new (or strengthening of) storm surge barriers and maintenance of the
coastal defence measures.
Dikes
Kok et al. (2008) based their estimates on several studies conducted for the
Rijkswaterstaat (Ministry of Public Works). These studies investigated the safety
standards of dike ring areas. Arcadis and Fugro (2006) conducted such a study for three
dike ring areas along the coast and the Central Planning Agency (CPB) of the
Netherlands did investigate these standards in the same time period (Eijgenraam, 2005;
2006) for a larger number of dike rings, including river dikes.
The cost estimates to raise the sea dikes are presented in Table 2-1 (Arcadis and Fugro,
2006) and Table 2-2 (Eijgenraam, 2005). The cost estimates of Eijgenraam (2005) were
found to be linear with the dike heightening (Figure 2-7).
Table 2-1: Cost estimates of three coastal dike-ring areas (Arcadis and Fugro, 2006)
Arcadis and Fugro (2006)
Dike heightening North Sea dikes Western Scheldt dikes Averaged
[m] [M/km] [M/km] [M/km]
0.8 4.36 4.46 4.41
1.6 5.82 6.37 6.095
2.4 7.3 8.28 7.79
11
Table 2-2: Cost estimates of coastal dike-ring areas (Eijgenraam, 2005)
dike heightening
CPB Cost estimates (Eijgenraam, 2005)
0.5 0.75 1
Dike ring
number Name [M/km]
15
Lopiker- en Krimpenerwaard 6.8 8.9 11.1
16
Alblasserwaard en Vijfheerenlanden 8.5 11 13.3
22
Eiland van Dordrecht 6.6 8.4 10.2
23
Biesbosch (Noordwaard) 2.5 3.2 4.3
24
Land van Altena 3.5 4.7 6.1
35
Donge 4.7 6.4 7.9
Average costs 5.4 7.1 8.8
y = 6,7667x + 2,0417
0,0
2,0
4,0
6,0
8,0
10,0
0 0,2 0,4 0,6 0,8 1 1,2
dike heightening [m]
costs [M/km]
Averaged costs f unction
coastal dike rings
Linear (Averaged costs
function coastal dike rings)
Figure 2-7: Averaged cost function of coastal dike-ring areas (Eijgenraam, 2005)
Nourishments
Due to the availability of nourishment material and the large amounts of beach
nourishments in the Netherlands the costs of nourishments in the Netherlands used to
be relatively low. Arcadis and Fugro (2006) estimated these costs to be 2.85 euro per
m
3
, where Kok et al. (2008) used a slightly higher number: 3 euro/ m
3
.
However, both the Ministry of Transport, Public Works and Water Management (RWS,
2009) and the Algemene Rekenkamer (2009) (‘court of audit’) noted that the costs of
nourishments in the Netherlands have increased rapidly over the last five years (Figure
2-8).
12
Figure 2-8: Price development nourishments in the Netherlands (RWS, 2009)
In the Netherlands more nourishments are required in the coming years and the
Deltacommittee (2008) anticipates even larger amounts of sand are needed in the (near)
future. Therefore, at the Ministry of Transport, Public Works and Water Management
(RWS, 2009) there is a concern about the current price development of nourishments.
Due to the current market situation; e.g. the limited number of large contractors
available, the international market-prices and the large increase in demand the prices of
nourishments have increased significantly. The Algemene Rekenkamer (2009) informed
the Dutch parliament about this situation in a letter (Algemene Rekenkamer, 2009).
Structural increase in cost prices from 2004 till 2009 (in 2009 price level) as determined
by RWS/ Ministry of Transport, Public Works and Water Management (2009):
•
Foreshore nourishments: from
1.11 to
3.72 (Figure 2-9)
•
Beach nourishments: from
2.54 to
7.55 (Figure 2-10)
13
Figure 2-9: Price development foreshore nourishments in the Netherlands (RWS, 2009)
Figure 2-10: Price development beach nourishments in the Netherlands (RWS, 2009)
Maintenance
The yearly costs for management and maintenance for primary flood defences in the
Netherlands is estimated to be approximately
350 million per year (AFPM, 2006). With
a total length of primary flood defences of about 3600 km the estimated costs for
management and maintenance become
100,000 per km flood defence per year.
14
Unit costs and relation to sea level rise (Kok et al., 2008)
Table 2-3 provides an overview of the unit cost prices as applied for the Netherlands.
Table 2-3: overview cost estimates the Netherlands
The Netherlands
Dike (Millions per km)
Dike heightening (per m)
• 9 – 10.8 (rural) (Kok et al., 2008)
• 18 – 21.6 (urban) (Kok et al., 2008)
• 4 – 11 (rural) (Eijgenraam, 2006)
• 6.9 (rural) (Fugro and Arcadis, 2006)
•
13.8 (urban) (Arcadis and Fugro, 2006)
Beach Nourishment ( per
m
3
material)
• 2.3 – 6.7 (Stive, pers. comm., 2009)
• 3 (Kok et al., 2008)
•
2.85 (Arcadis and Fugro, 2006)
• 3.72 (Foreshore nourishments) (RWS, 2009)
• 7.55 (Beach nourishments) (RWS, 2009)
Maintenance
0.1 M/km flood defence/year (AFPM, 2006)
Kok et al. (2008) applied these cost prices to determine the costs of sea level rise for the
Netherlands. Therefore several factors need to be applied to the unit costs to determine
the costs of the coastal defence system. These factors include the length of the coastal
defences, the cost of storm surge barriers (section 2.4) and the costs of beach
nourishments. Also the required height of the defence measures was determined based
on its relation with sea level, by several conversion factors. As shown in Table 2-3 a
different unit cost for rural and urban areas was applied. The results of this exercise are
shown in Figure 2-11, depicting the contribution of several aspects of the coastal water
system.
15
0
20
40
60
80
100
120
140
160
0123456
Sea level rise [m]
Costs of water system sea [B]
Sandy coast
Storm surge barriers
Sea dikes
Total
Figure 2-11: Cost function of coastal water system (Kok et al., 2008)
2.2 New Orleans (U.S.)
2.2.1 Background, history
New Orleans is situated in the delta of the Mississippi River (Figure 2-12). The city
originated at the natural levees (higher grounds) along the Mississippi river. On the North
side the city bounded by Lake Ponchartrain. Over time New Orleans gradually expanded
into the marsh area in between the Mississippi river and Lake Ponchartrain and from the
West Bank of the river further to the South.
Figure 2-12: Location of New Orleans in the state Louisiana of the United States
(Wikipedia)
16
Currently, the city and its surrounding suburbs make up a metropolitan area that is partly
below sea level and entirely surrounded by levees (American synonym for dikes). Since
a large part of the city is below sea level (around 50%), with an average elevation
between one and two feet (0.5 m) below sea level the area has a polder character and
can be considered a
bowl in between high waters (river and lake; see Figure 2-13).
Figure 2-13: Geological cross-section of New Orleans
(www.tulane.edu/~sanelson/Katrina/katrina_images.htm)
Because New Orleans is constructed on marsh area, large parts of the city continue to
sink. The soft sand, silts and clay beneath the city settle over time because of natural
consolidation but also groundwater pumping. The marsh area around the city also shows
subsidence and due to the lack of sediment input from the river, this area deteriorates at
a high rate.
As a consequence of its geographical situation, the area is vulnerable to flooding from
hurricanes, high discharges of the Mississippi River and heavy rains. Large-scale
pumping systems are installed for dewatering the city from rainfall and levees along the
river, Lake Ponchartrain and the marsh areas of the Mississippi delta protect the city
from storm surges. The vulnerability to flooding from hurricanes was tragically shown
when 80% of the city flooded when it was hit by hurricane Katrina in 2005.
2.2.2 Coastal defence measures
The New Orleans area consists of three levee rings (Figure 2-14) and has a safety
standard of a 1/100 year storm surge. These levee rings are constructed of Mississippi
river levees along the Mississippi river (considered outside the scope of this study),
hurricane levees along Lake Ponchartrain (Figure 2-15) and the marsh areas on the
South and East and storm surge barriers (under construction). In the city levee ring (#1)
several outfall canals are constructed which used to be in direct contact with the waters
of Lake Ponchartrain. Along these canals floodwalls are constructed (see Figure 2-15).
New Orleans is situated in the Mississippi delta and the surrounding areas are marsh
areas. These wetlands can be regarded as a natural storm surge defence system, since
the marshes cause storm surge energy dissipation. The costs of these areas are hard to
determine, however, marsh-creation and marsh-restoration costs can be estimated.
17
Figure 2-14: Levee rings New Orleans (Dijkman, 2007)
Figure 2-15: Lakeview levee and outfall canal floodwall (photo: Royal Haskoning)
Figure 2-16: Schematic cross-section New Orleans levee (Dijkman, 2007)
2.2.3 Cost estimates
Floodwall
In New Orleans often concrete floodwalls are constructed on the top of levees to
heighten the levee (Figure 2-17). After the flooding of hurricane Katrina in 2005 many
18
floodwalls needed to be reconstructed. The data on the costs of these constructions
varies due to different construction methods, but due to the reconstruction some
construction cost data was available.
Figure 2-17: Two types of New Orleans floodwalls: T-Wall (left) and I-Wall (right) (Tulane,
2008)
Bos (2008) used costs of different types of concrete floodwalls to determine the optimal
safety standard of the New Orleans East polder (Figure 2-14, #2). The costs were
derived from historical construction costs. To determine the unit costs, the costs of
floodwall per m heightening were derived in this study (Table 2-4).
Table 2-4: Overview of costs of different type of floodwalls (Bos, 2008)
Type of floodwall $/Ft /m M/km
height
(m)
costs in
M/km per m
heightening
7-Foot High L-Wall with 6-Foot Wide Monoliths 3200
7874
7.87
2.13
3.7
8-Foot High T-Wall with 8-Foot Wide Monoliths 3400
8366
8.37
2.44
3.43
10-Foot High T-Wall with 8-Foot Wide Monoliths 4100
10089
10.09
3.05
3.31
12-Foot High T-Wall with 11-Foot Wide Monoliths 5100
12549
12.55
3.66
3.43
14-Foot High L-Wall with 11-Foot Wide Monoliths 6300
15502
15.50
4.27
3.63
16-Foot High L-Wall with 11-Foot Wide Monoliths 7000
17224
17.22
4.88
3.53
18-Foot High L-Wall with 13-Foot Wide Monoliths 8300
20423
20.42
5.49
3.72
20-Foot High T-Wall with 14-Foot Wide Monoliths 9900
24360
24.36
6.1
3.99
22-Foot High T-Wall with 16-Foot Wide Monoliths 10800
26575
26.58
6.71
3.96
24-Foot High T-Wall with 17-Foot Wide Monoliths 12200
30020
30.02
7.32
4.1
26-Foot High L-Wall with 6-Foot Wide Monoliths 14600
35925
35.93
7.92
4.54
28-Foot High L-Wall with 6-Foot Wide Monoliths 15500
38140
38.14
8.53
4.47
30-Foot High L-Wall with 6-Foot Wide Monoliths 16800
41339
41.34
9.14
4.52
Hurricane levees
The costs of sea dikes (hurricane levees) are based on the Dutch perspective on coastal
Louisiana study (Dijkman, 2007), conducted by a team of experts from the Netherlands
19
as part of the Louisiana Coastal Protection and Restoration planning and technical effort
(LACPR).
The main design principle used is an earth fill levee body with a flexible asphalt
protection cover on top. This design allows for flexibility in settlement and can safely deal
with considerable wave overtopping without the risk of a levee breach. Redundancy in
the design (applied as flexible asphalt protection) aims to reduce the possibility of a
catastrophic breach in a levee in case of wave overtopping or surge overflow. This
design consideration will result in strong and redundant structures, but also in relatively
costly levees.
The main dimensions of the levee have been derived from the surge level and the wave
conditions. Slopes of 1:6 have been chosen at the surge side. Such slope is cost-
effective for wave energy dissipation. The inner slope is chosen at 1:4, which is a safe
value considering overflow and soil mechanical stability.
The proposed levee construction principles for upgrading existing of Dijkman (2007) are
identical to the principles applied for the design of new levees. Dijkman (2007)
determined unit cost prices for New Orleans levees to be 5 to 8 million euro per
kilometer for a meter dike heightening.
The focus in the Dutch perspective study is on so-called levee-rings (Figure 2-14). The
levee rings, considered in the Dutch perspective on LACPR, consist of the following
elements. Where openings are needed in such a ring (for shipping for example) a storm
surge barrier is constructed.
•
The construction of new levees
•
Upgrading of existing levees
•
Constructing storm surge barriers in navigation canals
•
Construction in storm surge barriers in waterways that are currently in open
connection with the Gulf of Mexico
The unit cost price of levee strengthening depends on the expected height of the levee
and hence on the return period of the design water level (Figure 2-18). As mentioned
above, the costs are considered relatively high, because the levees are constructed as
unbreachable levees by the flexible asphalt protection. Table 2-5 provides an overview
of the different levee upgrading costs and the costs for new alignment of hurricane
levees for a range of return periods.
20
2
3
4
5
6
7
10 100 1000 10000 100000
Return peri od [years]
Water level [m]
Figure 2-18: storm surge levels along Lake Ponchartrain (after Dijkman, 2007)
Table 2-5: Levee costs for return periods as determined by Dijkman (2007)
Return Period [years]
Price [M/km] 50
100
500
1000
5000
10000
100000
1E+06
Upgrade existing levees
14.5
19.2
22.6
26.1
29.8
33.5 41.5
50
New alignment levee 35.7
37.8
44.4
46.7
51.4
56.1 66.1
76.7
Armoring
Personal communications with Ray Devlin (Haskoning Inc.) gave an overview of the
costs of levee armoring (Table 2-6). These costs reflect the averaged cost prices quoted
by armoring vendors of three types of armoring. Although they include labour-, plant-,
and material costs, they are believed to not accurately reflect difficult site working
conditions. Therefore, these numbers will probably increase once account has been
taken of the large plant and restricted access required to work in very remote and
inaccessible areas.
Table 2-6: costs of armoring for levees in New Orleans (Devlin, pers. comm. 2010)
Installation costs including labour-, plant-, and material costs
Type of armoring [$/SY] [/m
2
]
Fabrics and Filled Mat 16.4 14.51
Open Mat 33.4 19.56
Concrete systems/ACB 126.9 11.31
Marsh restoration
In Dijkman (2007) also ecological restoration is considered, there the restoration and
stabilization of marsh areas around New Orleans was considered. It is expected that
these marshes reduce the wave run-up and hence reduce the flood risk. By several
measures (Figure 2-19) and via fresh water diversions the marsh areas are stabilized.
For marsh restoration the following activities where expected:
•
The development of ridge-levees
21
•
Salt water marsh restoration
•
Fresh water cypress swamp creation by hydraulic fill
•
Fresh water cypress swamp creation by artificial polders
•
The development of structures to divert fresh water, nutrients and sediments from
rivers to wetlands.
Figure 2-19: Measures undertaken for marsh stabilization (Dijkman, 2007)
Not the whole marsh restoration- and stabilization process is explained, but the costs to
stabilize large marsh areas in Barataria Bay and around Lake Ponchartrain were
provided. The unit costs are derived from these costs, taking into account the one-time
investments for structures to enable marsh stabilization (Table 2-7).
Table 2-7: Unit costs of coastal defence measures in New Orleans
New Orleans
Dike (Millions per km)
Dike heigthening per m:
5 – 8 (Dijkman, 2007; Jonkman et al., 2009)
Concrete floodwall; L/T-wall
type (M per km per floodwall
height)
3.7 – 4.5 (Bos, 2008)
Marshland stabilization
Marshland stabilization
• 1.4 /m
2
(Dijkman, 2007)
Marshland creation
• 3 /m
2
(Dijkman, 2007)
Freshwater diversion/culvert
• 10 M (Dijkman, 2007)
Marshland stabilization costs ( per m
2
per year)
• 0.07 (Dijkman, 2007)
Closure dam (M
per km per
m height)
3.7 (in water) (Dijkman, 2007)
Levee armoring ( per m2) 14.5 – 19.6 (Devlin, pers. comm. 2010)
22
2.3 Vietnam
2.3.1 Background, history
The Socialist Republic of Vietnam is with 88.6 million inhabitants a densely populated
country in South East Asia (CIA World Factbook, 2009). From North to South the country
is 1,650 kilometers in length and only 50 kilometers across in its narrowest point.
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 3,260 kilometers. The
coastal areas of Vietnam are subject to almost yearly flooding by typhoons formed in the
South China Sea.
Many activities take place in the fertile, but also vulnerable coastal areas. The river
deltas are the most densely populated areas of Vietnam and are prone to flooding from
both the rivers and the sea. Although the river deltas are low-lying areas of land, all
coastal land is above mean sea level. In the Northern and Southern part of Vietnam the
coastal land is, from shoreline to approximately 20 kilometers inland, between 0.5 and
10 meters above mean sea level (Figure 2-20). In central Vietnam some higher areas
are found.
23
Figure 2-20: Population density within and outside 10m low elevation coastal zone;
Vietnam (Columbia University; http://sedac.ciesin.columbia.edu/gpw/lecz.jsp)
The government of Vietnam wants to use the coastal zone to its fullest potential. This is
illustrated by one of the objectives stated after the dike breaches in Nam Dinh province
(Northern Vietnam) in 2005. The coastal defence strategies of Vietnam with respect to
sea dikes, their construction and maintenance are the responsibility of a ministry and
several dike departments. In total they maintain over 3,000 kilometers of coastal and
estuarine dikes. A large sea dike project to review and upgrade the sea dikes of Vietnam
and also formulate new guidelines for the construction of sea dikes was initiated in 2007.
The current state of many of the sea dikes is far from optimal and many breaches of sea
dikes in the Northern coastal provinces of Vietnam showed this vulnerability.
24
2.3.2 Coastal defence measures
For the Vietnam case study modern sea dikes have been investigated. In Vietnam there
is no land area below sea level, dikes are constructed because of storm surges, river-
and rainfall flooding and typhoon flooding.
Figure 2-21: New sea dikes in Vietnam (Nam Dinh province)
In some parts of Vietnam a tandem dike system is in place, however that system is not
considered in this study. The cost estimates in this chapter are based on completely new
sea dikes that have been and are constructed in Northern Vietnam in rural areas (Figure
2-21). These dikes consist of a sand/clay body and have revetments on the sea side of
the dikes. The dikes have relatively steep slopes and are constructed up to heights of 8
m. A typical Vietnamese dike profile is shown in Figure 2-22.
25
Figure 2-22: Representative cross sections of sea dikes in Nam Dinh province (Northern
Vietnam) (adjusted from Mai, 2004)
2.3.3 Cost estimates
The costs of the Vietnam sea dikes were investigated to determine safety standards for
the Northern provinces of Vietnam. Dike costs vary because of varying costs of material,
land use and applied inner/outer protection or revetments. The costs of labour are highly
variable, but relatively small and labour is often paid for by local departments – no clear
insight into labour costs was obtained.
Hillen (2008) determined the costs of dike construction by data of local dike
departments, cost data of stretches newly constructed sea dikes and interviews with dike
departments, ministries and academic staff of the Hanoi Water Resources University.
The dike costs as presented by Hillen (Figure 2-23) represent a new type of sea dike in
the Northern provinces with only sea side revetment. This concerns dikes in rural areas
where land-use costs are small. The dikes did not account for wave run-up and wave
overtopping. Based on dike department and ministry budgets, the yearly dike
maintenance costs for a 1 kilometer dike stretch were estimated to be 20,000
/km.
In parts of the Northern provinces experiments with mangroves are conducted. The
mangroves are re-introduced at some coastal areas as a natural barrier in front of sea
dikes. Since the effects of these mangroves were not yet tested and only very young
mangroves were placed in wetlands in front of the sea dikes, these costs are not taken
into account in this study.
26
0
1
2
3
4
5
6
7
8
9
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10
Dike he ight [m]
Costs [M/km]
Dike body
Land-use
Berm
Revetment
Total costs
Figure 2-23: Costs of dikes as a function of dike height according to Hillen (2008)
Mai et al. (2008) determined costs of dike heightening in an effort to illustrate a
comparable probabilistic approach to determine safety standards of Vietnam. Mai et al.
determined the safety standards for the Nam Dinh province, so this concerns dikes in
rural areas. The background of his cost data is unknown, but comparable safety
standards to Hillen (2008) were found. The costs of dike heightening are also
comparable to the costs as determined by Hillen. Mai et al. (2008) used both outer- and
inner slope protection and included the costs of maintenance in his dike costs graphs
(Figure 2-24) (Note that the costs in this figure are given in US$).
27
Figure 2-24: Dike heightening costs according to Mai et al. (2008)
The costs of the coastal defence for the Vietnam case study are based on the two
previously mentioned studies. Relatively little data is available on sea dike construction
in Vietnam and most of the data presented here is based on estimates, basic
calculations and interviews.
Table 2-8: Unit cost estimates Vietnam
Vietnam (Northern provinces: Hai Phong, Nam Dinh)
Dike heightening per meter
for a kilometer stretch in
Millions
• 0.7 – 1.2 (Hillen, 2008)
•
0.75 (Mai et al., 2008)
Maintenance
• 0.02 M/km dike/year (Hillen, 2008)
•
0.03 M/km dike/year (Mai et al., 2008)
2.4 Storm surge barriers
In various locations around the world storm surge barriers have been constructed.
Famous examples are the storm surge barriers in the Netherlands (Figure 2-26) in the
Southwest of the country.
In New Orleans a storm surge barrier is being built after Katrina at the eastern side of
New Orleans to protect the city from surges and reduce the length of the directly
exposed system (see Figure 2-25). Storm surge barriers are often chosen as a preferred
alternative to close of the estuaries and reduce the required dike strengthening behind
the dams. Another important characteristic is that they are often partly opened during
normal conditions and this will allow the tide and saltwater to enter the areas behind the
barrier. An overview of the main characteristics of storm surge barriers around the world
is given in Table 2-9.
28
Figure 2-25: Construction of the Inner Harbour Navigation Channel/St. Bernard storm
surge barrier (photo Royal Haskoning)
Figure 2-26: Maeslant storm surge barrier (near Rotterdam) and the Eastern Scheldt barrier
(South-Western delta)
29
Table 2-9: Overview storm surge barriers
Name barrier Type Year
Width
[m]
Height
[m]
Head
[m]
Construction
costs [M]
Construction costs
2009 price level [M]
the Netherlands
Measlant barrier (New
Waterway, Rotterdam) Floating sector
gate 1991 360 22 5 450
*1)
656
Hartel barrier (Hartel
channel) Vertical lifting
gates 1991 170 9.3 5.5 98
*2)
143
Eastern Scheldt Barrier Vertical lifting
gates 1986 2400 14 5 2500
*3)
4021
Ramspol (near IJssellake) Bellow barrier 1996 240 8.2 4.4 100 132
Europe
Ems (Germany) Sector gates 1998 360 8.5 3.8 290 368
Thames (Great-Britain) Sector gates 1980 530 17 7.2 800 1449
Venice MOSE project
(Italy) Flap gates 2010 3200 15 3 4678 4678
New Orleans
Seabrook barrier (New
Orleans) Vertical lifting
gates/sector gates 2010 130 8 4 114.7
*4)
115
IHNC barrier (New
Orleans) - only gates (excl.
floodwall) Sector gates 2010 250 8 4 518
*5)
518
Remarks Table 2-9:
1) Maeslant barrier has a relatively low cost price due to heavy competition for the contract.
2) The Hartel barrier has one very large horizontal span which increased the cost price.
3) The Eastern Scheldt barrier is relatively inexpensive due to its repetitive character.
4) The Seabrook barrier (New Orleans) has two different types of gate in a small span.
5) From the IHNC/St. Bernard storm surge barrier only the parts containing the gates have been taken into account, the floodwall was excluded.
30
The costs of a storm surge barrier depend on many factors, such as the type of
barrier/gates, the local soil characteristics, the desired height and hydraulic head over
the barrier. A first attempt to provide an estimate of a unit cost price per unit width has
been given below. The cost price per unit width has been deduced from the available
data. This ranges between 0.5 M
per meter width and 2.7 M
per meter width.
As the hydraulic head will be an important determinant for the forces on the barrier and
the required construction properties and costs, the relationship between the head and
the unit cost prices has been plotted (Figure 2-27). It shows that there is a weak
relationship between the head and the unit costs for storm surge barriers. It is
recommended to further investigate which factors determine the unit costs for storm
surge barriers.
y = 0,2959x + 0,074
R
2
= 0,2648
0
0,5
1
1,5
2
2,5
3
3 4 5 6 7 8
head [m]
costs / length [M/km]
Figure 2-27: Storm surge barrier unit cost estimates; costs per unit length vs. the
hydraulic head for the nine barriers shown in Table 2-9.
31
3 Coastal defense cost estimates and analysis
3.1 Unit cost prices for coastal defences
3.1.1 Overview
In this study we have analysed information on the costs of coastal defences for a
number of different areas. Table 3-1 summarizes some of the main characteristics of
these case studies areas. The results for Cape Town (SA) have been obtained from
appendix I. Although all the case studies have different conditions and circumstances, it
can be stated that the first three case studies are representative for a low-lying delta
coast, whereas the Cape Town case is more representative for a coast that is more
variable in terms of elevation and protection and coastal management strategies.
Table 3-1: Overview main characteristics case study areas
Standard of
protection [per
year]
Main threat for
coastal
defences
Surge level for
design
conditions [m]
Wave height for
design
conditions [m]
Netherlands 1/4000 – 1/10000 Storm surge 6 8
New Orleans (LA,
USA)
1/100 Hurricane 6 – 12 2
Vietnam 1/50 (expert
judgement)
Typhoon 4 – 10 5
Cape Town (SA) - Storm surge 1.6 11*
* value for a 100 year return period (off-shore)
The unit cost data as provided in Table 3-2 is based on cost estimates as found on
project level. These studies and projects were not intentionally set up to determine unit
costs, but did include coastal defence cost estimates for a number of different reasons.
The costs in Table 3-2 can be considered all in costs, which means they account for the
total engineering process. However, the results of the different case studies show a large
variability. Although for some estimates ranges are provided, it must be noted that cost
estimates largely differ from project to project and can be considered location
dependent. It can be stated that the unit cost of Table 3-2 largely reflect the Dutch
perspective on coastal defence costs, since most of the data was determined by Dutch
projects.
As mentioned, the available information on unit cost estimates for the case studies has
been summarized in Table 3-2. These numbers provide a first indication based on
studies for the four cases. There are several issues and uncertainties associated with
the interpretation of these unit numbers and their use in the context of national or global
studies on adaptation of the coastal defences to sea level rise. These issues are
discussed in section 3.2 to 3.4.
32
Table 3-2: Unit costs of coastal defence measures, converted to 2009 price levels
Unit Cost (2009 price levels)
Country and
locality if
appropriate
Vertical Seawall
(Million per
km length)
Dike (Millions per km)
Beach Nourishment
( per m
3
material)
Storm surge
barriers Other Measures
NETHERLANDS
National
- Dike heightening (per m)
• 9 – 10.8 (rural) (Kok et
al., 2008)
• 18 – 21.6 (urban) (Kok
et al., 2008)
• 4 – 11 (rural)
(Eijgenraam, 2006)
• 6.9 (rural) (Fugro and
Arcadis, 2006)
• 13.8 (urban) (Arcadis
and Fugro, 2006)
• 2.3 – 6.7 (Stive,
pers. comm.,
2009)
• 3 (Kok et al.,
2008)
• 2.85 (Arcadis and
Fugro, 2006)
• 3.72 (Foreshore
nourishments)
(RWS, 2009)
• 7.55 (Beach
nourishments)
(RWS, 2009)
Maintenance
0.1 M/km flood defence/year (AFPM,
2006)
UNITED STATES
New Orleans
Concrete
floodwall
construction; T-
wall type (per m
floodwall height)
• 3.7 – 4.5
(Bos, 2008)
Dike heightening (per m):
• 5 – 8 (Dijkman, 2007;
Jonkman et al., 2009)
-
Costs per unit width
(m) of a storm surge
barrier
0.5 – 2.5 M (this
study)
Unit costs related to
hydraulic head over
barrier (m).
Marshland stabilization
• 1.4 /m2 (Dijkman, 2007)
Marshland creation
• 3 /m2 (Dijkman, 2007)
Freshwater diversion/culvert
• 10 M (Dijkman, 2007)
Marshland stabilization costs (
per m2 per year)
• 0.07 (Dijkman, 2007)
Closure dam (M per km per m
height)
• 3.7 (in water) (Dijkman, 2007)
Levee armoring (/m2)
• 14.5 – 19.6 (Devlin, pers. comm.
2010)
33
Unit Cost (2009 price levels)
Country and
locality if
appropriate
Vertical Seawall
(Million per
km length)
Dike (Millions per km)
Beach Nourishment
( per m
3
material)
Storm surge
barriers Other Measures
VIETNAM
Hai Phong/Nam
Dinh
- Dike heightening (per m)
• 0.7 – 1.2 (Hillen, 2008)
• 0.75 (Mai et al., 2008)
-
- Maintenance
• 0.02 M/km dike/year (Hillen,
2008)
• 0.03 M/km dike/year (Mai et al.,
2008)
SOUTH AFRICA
Cape Town
(Geldenhuys, 2010;
appendix I of this
study)
0.3 – 3.96
-
• 1.2 – 1.5 M per
km beach (note:
different unit than
other nourishment
indicators)*
• 14.3 (Mather,
2009)
- Managed retreat
• 180 - 290 per m2 surface
* The actual amount of nourishment material per beach was not available for this study; this number was included to give a rough indication. This
indicates that the nourishment costs for the non-generic South-African coastline are much higher than for the Netherlands situation.
34
3.1.2 Comparison with IPCC CZMS (1990)
In the past, unit cost prices of coastal defence measures have been determined by IPCC
CZMS (1990) and later adjusted by Hoozemans et al. (1993). In the IPCC CZMS (1990)
effort the costs of a number of typical coastal defence measures were calculated based
on assumed standard dimensions of these measures. With material costs and
assumptions based on construction ‘all-in’ costs for several coastal defence measures
were determined.
Table 3-3: Comparison unit costs IPCC CZMS (1990) with findings of this study
Type of coastal defence
measure
Unit Cost IPCC CZMS (1990);
2009 price level
This study (the Netherlands);
2009 price level
New 1 m high sea dike 0.41 M
/km Not included, no real project
data available
New 1 m high sea dike with
regular maintenance 0.62 M
/km Maintenance costs: 0.1 M
/km
flood defence/year
Raising low sea dikes by 1
m in rural areas 0.52 M
/km Only existing (high) dikes taken
into account
Raising high sea dikes by 1
m in rural areas 1.04 M
/km 4 - 10.8 M
/km
Raising sea dikes by 1 m in
urban areas 10.39 M
/km 13.8 - 21.6 M
/km
Beach nourishment 3.12 - 6.24
/m
3
2.3 - 7.6
/m
3
Table 3-3 shows a comparison of the coastal defence measures found both in IPCC
CZMS (1990) and this study. In the table the dike construction costs are compared. The
method as applied by IPCC CZMS (1990) gives the costs for an ideal situation, the dike
heightening costs for the Netherlands as found in this study are therefore higher (both
for rural and urban conditions) than the estimated costs of IPCC CZMS (1990). This can
be attributed to the difference between an idealized dike of standard dimensions (as
applied by IPCC CZMS) and the actual construction costs, because in practice projects
often encounter more complex problems which cause an increase in costs. Hillen (2008)
determined the costs of the Vietnam sea dikes in a similar way as by IPCC CZMS (1990)
and these costs can be considered comparable.
The fact that coastal defence costs on project level are higher compared to idealized
dikes was also found in a study to include the costs of dike construction in a flood
damage computer model (Royal Haskoning, 2007). In that study it was concluded that to
determine the costs of flood defence measures in the Netherlands (both river-, lake- and
sea dikes) one could not rely on calculations based on a idealized dike cross-section
and unit costs of materials. In the report it is stated that ‘due to the large number of
variables, no cost calculation with unit costs is applied (…) instead expert judgement is
used to provide dike construction cost estimates including ranges.’ There is a large
difference between theory and practice. The increase in costs between IPCC CZMS
35
(1990) and Hoozemans et al. (1993) may also be attributed to this effect, as Hoozemans
et al. (1993) focused on the construction of a type of dike section.
The coastal defence unit cost estimates of this study are intended to contribute to the
global effort to determine unit costs (Linham et al. 2010). Compared to the numbers
found by Linham et al. (2010) especially the dike (heightening) costs of this study are
much larger. This accounts especially for the dike construction costs. It is recommended
that the dike construction costs are based on dike heightening and actual project data.
This gives comparable data and accounts for the additional costs that are always
included in large engineering projects.
3.2 Overview of factors that determine the unit cost price
General costs factors
In order to assess the cost of flood defences, a distinction can be made between five
different categories of factors that determine the costs (see below).
1. Planning and engineering costs
2. Material costs
3. Labour costs
4. Costs for implementation in the environment (urban or rural)
5. Costs for management and maintenance
Ad 1: Planning and engineering costs:
This concerns the dike design and planning of
the flood defence. In case of large uniform sections in rural areas, the unit costs may be
low, while in residential areas with non-uniform conditions, the unit cost are relatively
high.
Ad 2: Material costs:
The cost of materials is very site dependent. In deltaic regions,
there is sometimes scarcity of construction material (e.g. clay in New Orleans; stones for
revetments in the Netherlands). This highly influences the unit price and method of
construction.
Ad 3. Labour costs
: the cost of labour is varying a lot between countries. However,
when the cost of labour is low, labour is more intensely used, while in the case of
expensive labour, mechanized equipment is more widely applied.
Ad 4. Costs for implementation in its environment.
An important factor concerns the implementation of the flood defence in its environment.
Two main factors are:
- Land use by flood defences. The required width of a flood defence usually
increases with its height. The required amount of land has to be obtained, which
could be financially and legally and challenging and thus a costly and time
consuming task. However, in a rural environment, less challenges are expected.
- Rural or urban implementation. In an urban environment, space is usually scarce
and space-saving solutions are needed for the implementation of flood defence
projects. The solutions needed in urban environment (e.g. sheet piles) are
usually more expensive than the relatively cheap rural purchases of land.
Figure 3-1 gives an illustrative example that concerns the strengthening of a flood
defence. The first “round” of heightening does not lead to conflicts with the urban
36
environment. However, the second round would require alternative solutions or removal
of parts of the urban environment.
First round of
strengthening
second round of
strengthening
Figure 3-1: Example of strengthening of a flood defence and possible conflicts with the
existing urban environment.
Ad 5) Costs of management and maintenance
An organization is needed for the management and maintenance of flood defences. This
will result in an additional percentage of cost on the total expenses. The management
and maintenance in the Netherlands is carried out by so-called Water Boards. In other
countries there are usually also (semi-) governmental bodies for management and
maintenance.
To give an indication: The yearly costs for management and maintenance for primary
flood defences in the Netherlands is estimated to be approximately
350 million per
year (AFPM, 2006). With a total length of primary flood defences of about 3600 km the
estimated costs for management and maintenance become
100,000 per km flood
defence per year.
Discussion: Comparison of costs between countries
As mentioned above, the different unit costs vary per country and per location. The
differences between locations in a region will be largely determined by the exact design
and the implementation.
Country specific factors will be related to the local economic situation. The contribution
of the categories to the unit price is likely different is for each country. The costs for
material and labour will also affect the selected design, the materials used and the
construction method. In countries with low labour cost, and high material cost, another
choice is made for e.g. dike revetments than in countries with low material and high
labour cost.
The relative contributions may be compared. Though in case of comparison per country,
the development (GDP, specific education etc) needs to be taken into account. This is
be illustrated by comparing the derived average unit cost prices for dikes the three
countries (see section 3.1) to the GDP per capita (source: CIA World factbook; assumed
exchange rate 1 Euro = 1.34 US $). This shows that the estimated unit cost prices for
Vietnam are relatively high in comparison with the GDP per capita.
37
0
1
2
3
4
5
6
7
8
9
0 5000 10000 15000 20000 25000 30000 35000 40000
GDP per capita (Euro)
unit costs (10^6 Euro/m/km)
Vietnam
New Orleans
Netherlands
Figure 3-2: comparison between the average unit cost prices for dikes and the relationship
with the GDP per capita
3.3 Cost estimates at a system level
The unit cost of flood defences on a project level were discussed in the previous section.
In this section, we discuss some main factors and issues that determine the cost
estimates at a system level.
Main factors that determine the costs at a system level
The transition from unit cost prices to system level cost estimates are influenced by
three main factors:
1. Measures and solutions chosen for individual reaches
2. The system length
3. Modifications in the system’s alignment
Ad 1: the cost factors for individual projects have been discussed in section 3.2
Ad 2: system length
: the total cost for (adaptation) of a flood defence system is
determined by the length of the flood defences in the system. The total costs are found
by integrating the unit costs prices for invidual reaches over the total system length.
Obviously, the costs will be high for a system with a large length. A good example
concerns the protected areas that are found in the so-called Plaquemines area in
Louisiana, south East of New Orleans. These are wide scarcely populated areas along
the Mississippi that are protected by levees / dikes from river and hurricane flooding.
Due to the large system length protecting the values in this area will be relatively costly.
This also has a relationship with the cost benefit analysis and optimal protection level
that would be found for such an area (see also section 4). An area with a relatively low
economic value but high systems adaptation costs, will have a lower optimal protection
38
level (or “demand for safety”) than an area with a high concentration of values and a
relatively small systems length.
Figure 3-3: Plaquemines area in Louisana, SE of New Orleans. Green and purple lines
indicate the current levees. North to South is app. 120km.
Ad 3 Modifications in the system’s alignment
: The length of a coastal flood defence
system may be shortened by closing off estuaries. This could bring additional
advantages for for example navigation and agriculture (availability of fresh water), but
could also have negative effects on the ecological system. Such an adaptation is usually
done when the benefits (e.g. less costs due to a smaller system length and reduction of
the risk) outweigh the costs of such a modification (e.g. additional dams or storm surge
barriers). Examples of such projects are:
- Netherlands: construction of storm surge barriers, such as the Eastern Scheldt
and Maeslant barriers, to close of the estuaries and reduce the required dike
strengthening behind the dams and barriers (see Figure 3-4 for an overview of
some of the dams in the Dutch delta plan that was constructed after the 1953
storm surge disaster)
- New Orleans: A storm surge barrier is being built after Katrina at the eastern side
of New orleans to protect the city from surges and reduce the length of the
directly exposed system. In addition, gates were built in the outfall canals in the
north of the central city to prevent that the levees along these canals could be
directly exposed during surges (see Figure 3-5 for an overview – new gates and
barriers in red).
39
Figure 3-4: Overview of dams (indicated with numbers) that were constructed after the
1953 storm surge disaster in the Netherlands.
Figure 3-5: Overview of new dams and gates (in red) that were constructed in New Orleans
after hurricane Katrina (source: Times Picayune newspaper).
40
Costs made for other functions
The costs of a project will depend on the exact solution or measure that is chosen. A
measure or project will never be solely based on the flood defence requirements. The
flood defence function (and its cost) is in this case will only form a part of the total
project. Other functions (recreation, infrastructure, ecological quality etc.) will influence
the design as well. Multifunctional and integrated approaches become more and more
common and the total costs of these solutions would be generally higher than would only
be the case for the flood defence function. Examples of recent projects where this
played a role are given below.
- Room for Rivers in the Netherlands: Instead of heightening the river dikes, the
room for rivers strategy has been adopted. This strategy is more expensive than
strengthening the dikes. Ecological and landscape issues were were important
factors in the choice for this strategy.
- The ‘Sand engine’, which is a single sand nourishment that is large enough to
replace many years of future nourishments. While obviously involving a large
safety aspect, additional costs have to be made as more sand is needed for
merely ecological values.
- The plans for the multi-functional Afsluitdijk (closure dam) in the Netherlands: the
proposed multifunctional solutions have much higher costs than a basic
strengthening of the Afsluitdijk.
Figure 3-6: One of the proposed designs for the Afsluitdijk / closure dam in the
Netherlands, with several additional functions, such as nature development and tidal
energy generation.
- Multifunctional defence types and concepts:
o
Delta dikes, super levees that integrate wide dikes with spatial
development
o
Comcoast project: wide coastal zones that integrate coastal zones with
nature development.
41
Figure 3-7: Example of a multifunctional super levee in Japan that combines a flood
defence with urban development.
Figure 3-8: Example from the Comcoast project of a coastal development zone that
combines flood protection and nature development.
3.4 Relationship between sea level rise and coastal defence
costs
General
In this section we discuss the possible extrapolations of these coastal defence costs into
future expenses to adapt to sea level rise. One must carefully distinguish two
relationships:
1. The development of the hydraulic loads over time (largely determined by the sea
level rise rate) and the required adaptation of flood defences
2. The relationship between the adaptation of the flood defence and the the
associated costs
42
The combination of these two relationships determines the eventual the development of
costs of adaptation over time. If both relationships are linear, the costs will shows a
linear increase over time (see Figure 3-9). If one of the two relationships is non-linear,
the eventual development of costs over time will be non-linear as well. The underlying
factors are briefly discussed below.
time
Sea level Dike height
Costs
time
Costs
1) development of sea
level over time
2) costs of
adaptation of
the flood
defence
Figure 3-9: Conceptual scheme that shows how the development of adaptation costs over
time depends on the development of sea level rise and the relationship between costs and
sea level.
Adaptation of existing flood defence structures to sea level rise
It is noted that the required adaptation of flood defences will be based on the local value
of the relative sea level rise rate
1
. The combination of sea level rise and subsidence is
usually referred to as relative sea level rise. In New Orleans, it appeared that the crest
elevation of many of the levees and floodwalls around New Orleans was substantially
lower during hurricane Katrina than at the moment of design and construction due to the
effects of subsidence.
Regarding the adaptation of existing flood defence systems, one should consider
different design parameters and how they change with sea level rise. Parameters that
increase linearly with a constant SRL rate are:
- The required nourishment volumes
- Dike height
1
This means that subsidence of the land has to be considered in addition to the effect of sea
level rise. Subsidence can have several causes: Inclination of organic materials (which is usually
the case in delta), extraction of natural resources (oil, gas, water) and tectonic movement (e.g.
post-glacial rebound of Scandinavia causes subsidence in the Netherlands).
43
- Footprint of the dike and required purchases of land
Parameters that will increase not-linearly with a constant SLR rate are:
- the dike volume and thus the required amount of soil.
- Expected costs of implementation. The wider the footprint of the dike, the higher
the probability that houses or other buildings or objects have to be removed, or
that specific and costly measures have to be implemented to prevent this.
It depends on local circumstances which parameters are dominant, and thus it depends
on local circumstances whether the costs develop linear or non-linear.
Effects of the sea level rise rate
The future sea level rise (SLR) rate will determine required dike strengthening and
investments. In case of an existing dike system, this results in:
- Linear SLR rate: same strengthening every interval. Note that with a higher, yet
constant SLR rate, the costs will go up, but linearly.
- Non-linear (concave) SLR rate: the required strengthening becomes larger in
time.
Linear SLR: the heightening steps remain
constant.
time
Sea
Level
Dike height
Dike height /
Sea level
Exponential SLR: The heightening steps
increase in time.
time
Sea level
Dike height
Dike height /
Sea level
Figure 3-10: The effects of the sea level rise rate on the dike heightening steps
It must be noted that for instance for sea dikes, the required dike height goes up faster
that the SLR rate, as one has to incorporate the effect of increased wave height on the
dike design. However, the relationship will still be linear.
Findings for the Netherlands (Kok et al., 2008)
For the Netherlands a prediction of the development of the future costs of flood defences
has been made (Kok et al., 2008) as part of the investigation of the Deltacommittee. A
sea level rise scenario was assumed that concerned a sea level rise of 0.85m in 2100
and a total sea level rise of 2.0m in the year 2200. The development of costs for different
subsystems has been predicted. The figure shows the (average) yearly costs.
In general, a linear relationship between the costs of adaptation and the sea level rise
was found. The most important design and cost parameters (height, width, land use) of
the flood defences showed a linear increase over time. An important reason was that a
constant sea level rise rate was assumed. However, replacement of existing major flood
defence structures, such as storm surge barriers, was expected to lead to small “jumps”
in the cost function, see example below.
44
Figure 3-11: Development of yearly costs for flood defence in the Netherlands over time
(Kok et al., 2008).
Other considerations and factors
Several (other) factors will affect the development of coastal defence costs over time
and some of those have been discussed in the previous sections. A specific issue is the
prediction of cost estimates for future expenses. Several developments could to changes
in the unit cost price levels:
- uncertainty in development of costs and market prices (e.g. oil price)
- new innovative techniques with different price levels
Possible strengthening of the primary flood defence system could affect the internal
water management system, e.g. drainage and pumping systems, especially in low-lying
delta areas. For example if the sea level rises pumps with higher capacity are needed to
drain these areas.
An important driver for changes in coastal protection could be the economic and
population growth. This results in an higher need for safety and thus in the improvement
of flood defences. This effect is discussed in chapter 4. This could lead to the decision to
raise the level of protection. With that it could also be decided to adapt the alignment of
the system.
Linear or non-linear development of the costs of coastal protection over time?
In summary, it is not easy to determine whether the costs of flood defences and coastal
management will develop linearly or non-linearly over time. This will determine on local
factors that have been described above. Some important factors that would contribute to
a linear of non-linear development are summarized below:
Linear development (unit cost prices remain constant over time)
- Constant (relative) sea level rise rate
- Same measures can be used for higher design water levels
- Most design parameter increase linearly with a linear SLR rate
- Relative costs levels for labour and material remain constant over time
- No increase of the costs of purchasing land for additional widening and
strengthening
- Level of protection remains constant over time
45
Non-linear development (unit cost prices increase over time)
- sea level rise rate increases
- System modifications required (e.g. storm surge barrier replacements)
- Important design parameter increase non-linearly with sea level
- Construction of new flood defences required
- Relative costs levels for labour and material increase over time
- Adaptation of the defences requires measures in “difficult” areas, e.g. urban
areas
- Level of protection increases over time
There are factors that could contribute to a decrease of the unit costs over time. When
material or labour costs decrease or when new cheaper techniques and constructions
are invented the marginal costs of adaptation could decrease. The relationship between
sea level rise and costs will be determined by a combination of the above factors.
46
4 Optimal protection levels
This section focuses on the determination of optimal protection levels in a so-called
economic optimization or cost benefit analysis. The unit cost prices that have been
discussed in the previous sections will be important input, but not the only input, in
determining the optimal protection levels. The general approach and theory is presented
in section 4.1. Findings for the three case studies are included in section 4.2. Section 4.3
compares the results of the case studies with the demand for safety that follows from the
DIVA model.
4.1 Background and general approach
After the 1953 flood disaster a Delta Committee was installed to investigate the
possibilities for a new approach towards flood defence. The committee proposed to
reduce the vulnerability by shortening the coastline and closing off the estuaries in the
Southwest of the country. In addition, safety standards for flood defences were
proposed. In an econometric analysis the optimal safety level was determined for the
largest flood prone area, South Holland (van Dantzig, 1956). In this economic
optimization the incremental investments in more safety are balanced with the reduction
of the risk. The investments consist of the costs to strengthen and raise the dikes. In the
simple approach it was assumed that flooding could only occur due to overtopping of the
flood defences. Thereby each dike height corresponds to a certain probability of flooding
(the higher the dikes the smaller the probability of flooding). Dike heightening leads to
reductions of the probability of flooding and the expected damage (= probability x
damage). By summing the costs and the expected damage or risk, the total costs are
obtained as a function of the safety level. A point can be determined where the total
costs are minimal, this is the so-called optimum. The approach has been applied after
the 1953 storm surge to determine an optimal safety level was determined for the largest
flood prone area, South Holland.
The equation for the optimal protection level is as follows:
D
rBI
P
opt
'
=
Where:
•
P
opt
– optimal protection level [1/year];
•
I’ – costs per unit of heightening / strengthening of the flood defence;
•
r’ – nett discount rate (economic growth minus inflation);
•
B – constant related to the statistical distribution of the water levels [-];
•
D – potential damage in case of flooding [Euro]
This shows that the marginal costs of improvement of the safety and the potential
damage will be important factors that determine the optimal protection level. The other
two factors (B, r’) are generally constant and do not depend on regional or local
characteristics of the area under study. The economic optimization is often also referred
to as cost benefit analysis.
47
Figure 4.1: Principle of the Economic optimization approach by the Delta Committee.
In recent work (Eijgenraam, 2006) some modifications of the approach have been
proposed. In essence, the difference is that van Dantzig assumes one major
improvement at the current moment, while Eijgenraam considers the periodical character
of the improvement of the flood defence system under changing conditions such as
economic growth, sea level rise etc.. As a result the optimal flooding probability will
change over time, e.g. due to economic growth (see figure 4.2). Comparison of both
these methods for some practical case studies for the Netherlands and New Orleans
shows that they give similar results for the first decades of the considered time period.
Figure 4.2: Development of the optimal flooding probability over time (Kind et al., 2008)
48
4.2 Case studies
This section briefly presents the results for three case studies for which the method of
economic optimization was applied. Further background is given in the publications that
are referred to.
4.2.1 Netherlands
Background
After the 1953 disaster a delta committee was installed. The analysis of the Delta
Committee laid the foundations for the new safety approach, in which dikes are
dimensioned based on a design water level with a certain probability of exceedance. The
current design criteria and the process for safety evaluation of the flood defences are
based on these design water levels. This approach to flood protection is laid down in the
flood protection act of 1996. The flood prone areas in the Netherlands are divided in so-
called dike ring areas, i.e. areas protected against floods by a system of water defences
(dikes, dunes, hydraulic structures) and high grounds. The safety standards for the
various dike depend on the (economic) value of the area and the source of flooding
(coast or river). For coastal areas design water levels have been chosen with
exceedance frequencies of 1/4000 per year and 1/10,000 per year. For the Dutch river
area the safety standards were set at 1/1250 per year and 1/2000 per year. Some
smaller dike ring areas bordering the river Meuse in the south of the country have a
safety standard of 1/250 per year.
Recent economic optimization
More recently, the cost benefit analysis / economic optimization, has been applied to all
major dike rings in the Netherlands. This was done by applying the “dynamic” model
proposed by Eijgenraam (2006). A first indication of the results was presented in (Kind,
2008). The results are shown in figure 4-3. These are the so-called “middle” optimal
safety levels. This means that these are the middle probabilities in the bandwidth shown
in figure 4-2. When these results are compared with the current safety standards it is
found that especially in the dike rings in the river system in the east of the country would
need to receive a higher protection level than the current level. It is noted that the results
below are a first indication, as further extensive studies are ongoing. Final results will be
used for a possible update of the existing safety standards.
49
Figure 4.3: Optimal safety levels for dike rings in the Netherlands.
4.2.2 New Orleans
The economic optimization has been applied to New Orleans. As part of the broader
“Dutch perspective study” (Dijkman, 2007) the optimal safety levels for the three polders
that are shown in Figure 4.4 have been determined. Table 4.1 and Figure 4.4 give the
results for the central part of New Orleans (dike ring 1). As part of the approach design
surge levels and their return periods were determined. The costs have been based on
the unit cost estimates that have been presented in section 3. Damage estimates have
been used based on various studies that were published after hurricane Katrina.
50
Figure 4.4: Overview of New Orleans metropolitan area and proposed flood protection
systems in de Dutch perspective: (1) Northern dike ring 1 (central part of New Orleans); 2)
Northern dike ring 2 (East Orleans and St Bernard); (3) Southern levee ring (West bank).
Table 4-1: Economic optimization for Northern dike ring, central part of Orleans: Input
information and results
Return period (yr) 100 500 1,000 5,000 10,000 100,000 1,000,000
Design surge level
Lake Pontchartrain (ft) 9 11 13 15 17 21 25
Investments ($) 2.2E+09 2.4E+09 2.6E+09 2.9E+09 3.1E+09 3.6E+09 4.1E+09
0,0E+00
2,0E+09
4,0E+09
6,0E+09
8,0E+09
1,0E+10
1,2E+10
1,4E+10
1,6E+10
1,8E+10
10 100 1000 10000 100000 1000000
return period (yr)
Costs (US $)
Investments Risk Total costs
Figure 5: Results of economic optimization for the Northern dike ring, central part of New
Orleans
For the central area (northern dike ring 1) an optimal safety level of about 1/5000 per
year has been found. For the other two polders optimal safety levels of around 1/1000
per year were obtained. Given the preliminary character and the uncertainties in the
51
assumptions (See Jonkman et al., 2009 for discussion) the presented outcomes can be
regarded as a first indication.
4.2.3 Vietnam
In a number of publications the approach has been applied to Vietnamese sea dikes,
(Hillen, 2008; Mai et al., 2008; Mai, 2010). A case study has been done for the Nam
Dinh province, in the northern part of the country. This was also the area that was
seriously flooded after typhoon Damrey in the year 2005. This event caused about US $
500 million of damage. Based on cost estimates for the sea defences (see section 3),
information on typhoon induced surges and their return periods, and assessments of
damage in coastal areas the economic optimal level of protection was determined.
Figure 4.5 shows the results for Nam Dinh province for the current level of economic
development. This leads to an optimal protection level of about 1/50 per year. Vietnam
has a fast growing economy. If future economic development is taken into account,
leading to a growth of the potential damage, a higher protection level is found of about
1/90 per year.
Figure 4.5: Economic optimization for Nam Dinh province for the current economic
situation (Mai, 2010).
52
4.3 Discussion and comparison with the DIVA model
The results for the three case studies have been compared with the “demand for safety”
that resulted from the DIVA model (personal communications with Linham, 2010), see
table 4.2. It is clear that both approaches given different results.
Table 4-2: Comparison between the optimal protection level determined with the economic
optimization and the demand for safety that resulted from the DIVA model
Location Demand for safety according
to DIVA (return period [yr])
Optimal protection level
(return period [yr])
Netherlands 1739 (Amsterdam)
1396 (Rotterdam)
20,000 (Rotterdam area)
4000 (Amsterdam area)
(Kind et al., 2008)
New Orleans (USA) 1385 1000 – 5000 (Jonkman et al.,
2009)
Vietnam 14 (Hai Phong)
1 (Ho Chi Minh City)
50 (Nam Dinh, current situation)
90 (Nam Dinh, incl. economic
growth)
(Mai Van, 2010)
A further general comparison of similarities and differences between the two approaches
is given. Table 4-3 compares the factors that are included in the DIVA approach (Anon,
2010) and the factors that are included in the economic optimization.
Table 4-3: comparison between the factors included in DIVA and the economic
optimization
DIVA Economic optimization
• GDP
• Coastal population density
• Storm surge regime
Higher GDP and coastal populations generate
greater demand for safety
• Damage in case of flooding
• Marginal cost of improving the level of
protection (determined by system length and
costs of measures)
• Nett discount rate
• Return periods of hydraulic load levels
Generally speaking one can see that DIVA includes more general factors whereas the
economic optimization focuses on more specific factors that relate to the system’s
characteristics. This is not surprising as DIVA as used for global assessments, whereas
the economic optimization is more used as a design supporting approach for flood
defence systems.
Two important factors in the economic optimization are the potential damage and the
marginal costs of improving the level of protection. The information on the GDP and
coastal population density in DIVA are related to the damage potential. One additional
factor that is not included in DIVA but is important for the damage potential is the amount
of flood prone / low-lying areas in the considered region.
In the DIVA model the (marginal) costs of improving the level of protection are not
directly included. One important factor that will determine these costs will be the length
of the defence system. The longer the alignment, the more expensive raising the level of
53
protection will be. That the system’s length is an important factor was also found in the
economic optimization (Eijgenraam, 2006). For dike rings in the Netherlands it was
found the the optimal level of protection was directly related to the ratio of the number of
inhabitants and the system’s length (see figure 4.6). The number of inhabitants will be
proportional to the damage, and the system’s length will influence the costs of improving
the level of safety. These two factors (damage and marginal costs) are the most
important determinants of the optimal protection level (see also the formula in section
4.1). Following this approach a smaller system with a high concentration of people and
values will receive a higher optimal level of protection than a very long system with a low
population density.
Figure 4.6: Optimal safety level (return period) versus the number of inhabitants per unit
dike length (Eijgenraam, 2006).
The above shows that the number of inhabitants per unit of the length of the defence is a
good approximate measure for the optimal protection level. It is recommended to use
this measure as a representative for the optimal standard of protection, and to
investigate if and how the length of the defence system can be added to the approach
implemented in DIVA. More overall, it is recommended to compare the approach of the
economic optimization and the DIVA method for determining the “demand for safety” at a
methodological level and for a number of selected case studies.
54
5 Main findings and recommendations
Information on the costs of coastal defences has been investigated for the full range of
hard and soft engineering measures, such as dikes/levees, nourishments and storm
surge barriers. Information and cost estimates from previous studies have been used to
derive unit cost estimates for the Netherlands, Vietnam, New Orleans (LA, USA) and
Cape Town (South Africa)
An overview of the resulting unit cost estimates is given in table 3-1. Some main findings
are summarized below:
•
Dikes
: for the Netherlands the unit costs for strengthening of dikes range
between 4 and 11 M
per km per m heightening for rural areas and between 14
and 22 M
per km per m heightening for urban areas (2009 price levels). The
cost estimates for dike and floodwall heightening for New Orleans are between 4
and 8 M
per km per m heightening.
•
Storm surge barriers
: the cost price per unit width has been deduced from the
available global data. This ranges between 0.50 M
per meter width and 2.7 M
per m width
•
Beach nourishment
: for beach nourishment in the Netherlands the available
literature sources indicate a unit cost price of about
3-4 per m
3
material for
foreshore nourishment and
7-8 per m
3
material for beach nourishment. A
somewhat higher unit cost
11 per m
3
material for beach nourishment has been
obtained for South Africa.
•
The unit cost prices will depend on the measure selected and consequently on
the costs for planning and engineering, labour, equipment, materials. There are
two important factors:
1.
Local economic factors
: The average unit costs for dike strengthening
in Netherlands and New Orleans are about eight times higher than those
for Vietnam. It is necessary to use different cost estimates for regions with
different economic development levels.
2.
Implementation in urban or rural areas
: Additional costs have to be
made if measures are implemented in urban or ecologically sensitive
environments. For the Netherlands the unit cost price for strengthening
dikes in urban environments is about two times higher than the unit cost
price for rural areas
•
The costs estimates at the level of a coastal protection system will depend on the
unit cost prices, the system’s length, the chosen alignment and costs made for
other functions than coastal flood protection (e.g. recreation, ecology). All these
factors have to be taken into account when predicting the costs of adaptation to
sea level rise.
•
A comparison between the unit cost estimate from IPCC CZMS and the findings
of this study shows the following. The unit costs in the IPCC study are lower,
likely because the IPCC numbers are based on dike construction or
strengthening in an idealized situation, whereas the numbers from this study are
based on actual project data.
•
It has been investigated whether there is a linear or non-linear relationship
between the sea level and the costs for adaptation of flood defences. Current
55
studies for the Netherlands (Kok et al., 2008) suggest a linear relationship. A
number of factors have been identified that would affect this relationship.
Important factors are the sea level rise rate, future changes in price levels
(labour, materials), the need for modification of the system’s alignment and the
need for adaptation of large structures, such as storm surge barriers.
•
Given all these factors, the derived unit costs estimates should be considered as
indicative and they can only be applied with a considerable bandwidth /
uncertainty margin.
•
The optimal levels of protection that have been found by applying the economic
optimization / cost benefit analysis to three case studies differs from the “demand
for safety” that is found with the DIVA model. One important difference is that the
economic optimization takes into account the potential damage and the actual
length and improvement costs of the flood defence system, whereas the DIVA
model is based on more global indicators, such as the population density, GDP
and storm surge regime.
Recommendations
•
For consideration of the costs of measures at a system or higher level (country or
regional) it is essential to specify which measures are implemented. This means
that studies on the costs of adaptation to sea level rise would also require
specification of the (assumed) measures, the system alignment and the
strategies that are implemented.
•
Given the uncertainties and / or lack of knowledge of underlying factors it is
recommended to express unit cost estimate by means of bandwidths.
•
Further analysis of existing cost information for storm surge barriers is
recommended. It can be investigated whether a relationship between various
barrier characteristics (width, height, hydraulic head, barrier type) and the barrier
costs could be found. A general formula could be derived to give a first indicative
prediction of the costs of storm surge barriers.
•
In new Orleans approximately US $ 15 billion has been invested in recent years
to repair and improve the safety of the hurricane protection system. Although a
lot of cost information is confidential, analysis of public information on levee
projects could improve the empirical basis of the cost estimates for this region. It
is recommended to set up a specific investigation for this system.
•
It is recommended to review and update the county factors that are used in the
IPCC CZMS study based on more actual data from costs of coastal defence
projects and regional economic indicators.
•
In an economic optimization an optimal level of protection can be determined
based on the required investments in providing a higher safety level and the
benefits in terms of reduction of the economic risk. The investments will be highly
dependent on the design of the flood defence system for the system and possible
changes in the alignment and the implemented defence measures. A good
approximate measure for the optimal protection level is the number of inhabitants
per unit of the length of the defence. It is recommended to use this measure as
representative for the optimal standard of protection, and to investigate if and
how the length of the defence system can be added to the approach
implemented in DIVA.
56
•
More overall, it is recommended to compare the approach of the economic
optimization and the DIVA method for determining the “demand for safety” at a
methodological level and for a number of selected case studies.
57
6 References
Anonymous 2010. Optimal and applied safety standard. Ppt presentation.
AFPM (Advisory Committee Primary Waterdefences) 2006. Tussensprint naar 2015 –
advies over de financiering van primaire waterkeringen voor de bescherming van
Nederland tegen overstromingen.
Algemene rekenkamer (court of audit), 2009. Letter to the Dutch parliament. KST136835
Arcadis and Fugro, 2006. Kostenfuncties Dijkringgebieden 7, 14, en 29 (‘cost functions
dike-ring areas 7, 14 and 29’). Report for the Ministry of Transport, Public Works and
Water Management, the Netherlands.
Bos, A.J. 2008. Optimal safety level for the New Orleans East polder; A preliminary risk
analysis. MSc Thesis University of Amsterdam
CIA World Factbook, July 2009 estimate. https://www.cia.gov/library/publications/the-
world-factbook. Accessed April 2010.
Dijkman, J. (Ed.) 2007 - A Dutch perspective on coastal Louisiana flood risk reduction
and landscape stabilization. Contribution to LACPR study of USACE and state of
Louisiana.
Eijgenraam C.J.J. 2006. Optimal safety standards for dike-ring areas. CPB Discussion
Paper No. 62.
Eijgenraam, C.J.J. 2005. Veiligheid tegen overstromen; Kosten-batenanalyse voor
Ruimte voor de Rivier, deel 1; CPB Document No. 82.
Ericson, J.P., Vorosmarty, C.J., Dingman, S.L., Ward, L.G. and Meybeck, M., 2006.
“Effective sea-level rise and deltas: causes of change and human dimension
implications.” Global and Planetary Change, 50, 63-82.
Hillen, M.M. 2008. Safety Standards Project, Risk Analysis for New Sea Dike Design
Guidelines in Vietnam. Technical Report Delft University of Technology / Hanoi
Water Resources University; Sea Dike Project, pp.68.
Hoozemans, F.M.J, Marchand, M. and Pennkamp, H.A., 1993. “A global vulnerability
analysis: Vulnerability assessment for population, coastal wetlands and rice
production on a Global scale”, 2nd Edition. Delft Hydraulics, the Netherlands
IPCC CZMS, 1990. “Strategies for Adaptation to Sea-level rise.” Report of the Coastal
Zone Management Subgroup, Response Strategies Working Group of the
Intergovernmental Panel on Climate Change. Ministry of Transport, Public Works
and Water Management, the Netherlands, pp.122.
58
Jonkman, S.N., Kok, M., van Ledden, M. and Vrijling, J.K., 2009. “Risk-based design of
flood defence systems: a preliminary analysis of the optimal protection level for the
New Orleans metropolitan area.” Journal of Flood Risk Management, 2(3), 170-181.
Kind J. 2008. Waterveiligheid 21e eeuw – Kengetallen kosten baten analyse. Rapport
WD2008.044
Kind J. 2008. Cost benefit analysis to determine efficient flood protection standards for
the Netherlands. Proceedings of the 4th international conference on Flood Defence,
105/1 – 105/8
Kok, M., Jonkman, S.N., Kanning, W., Stijnen, J. and Rijcken, T., 2008. “Toekomst voor
het Nederlandse polderconcept.” (in Dutch) Appendix to “Working together with
water.” Deltacommittee 2008, the Netherlands
Linham, M.M., Green, C.H. and Nicholls, R.J. in preparation. “Costs of adaptation to the
effects of climate change in the world’s large port cities.”
Mai, C.V. et al. 2008 - Risk analysis of coastal flood defences: a Vietnam case. 4th
International Symposium on Flood Defence, Toronto, Canada.
Mai C.V. (2010) Probabilistic analysis and risk-based design of water defences in
Vietnam Draft PhD thesis, Delft University.
Nicholls, R.J., Hanson, S., Herweijer, C., Patmore, N., Hallegatte, S., Corfee-Morlot, J.,
Château, J. and Muir-Wood, R., 2008. “Ranking Port Cities with High Exposure and
Vulnerability to Climate Extremes.” OECD Environment Working Papers, No 1.
Royal Haskoning, 2007. Doorontwikkeling HIS SSM; definitiestudie naar kosten herstel
waterkeringen en opname in HIS SSM (study determine repair costs of flood
defences for HIS SSM) for RWS (Ministry of Transport, Public Works and Water
Management, the Netherlands).
RWS, 2009. Nourishment presentation of Alex Roos (Ministry of Transport, Public Works
and Water Management, the Netherlands) for the municipality of The Hague. Ppt
presentation.
Van Dantzig D. (1956) - Economic decision problems for flood prevention. Econometrica
Vol. 24 pp. 276-287
59
Appendix I – Coastal defence cost estimates Cape Town
(South Africa)
M.A. Geldenhuys BSc
Coastal Adaptation to Climate Change:
Measures and Costs
A Cape Town Case Study
M.A. Geldenhuys BSc (TU Delft – CoMEM program)
List of Figures: ...................................................................................................................... 3
1Introduction.................................................................................................................... 4
2Description of the Local Situation................................................................................... 5
2.1General................................................................................................................... 5
2.2Topography............................................................................................................. 6
2.3Bathymetry ............................................................................................................. 7
2.4Tides....................................................................................................................... 7
2.5Sea Level Rise and Surge ......................................................................................7
2.6Waves..................................................................................................................... 8
3Current Coastal Protection and Management Strategy ................................................12
4Overview of existing cost estimate information............................................................. 17
4.1General................................................................................................................. 17
4.2Estimated damage cost for specific storm event................................................... 19
4.2.1Details of Storm ............................................................................................. 19
4.2.2Recorded losses and damage ....................................................................... 19
5Discussion and conclusions......................................................................................... 21
5.1Challenges in terms of protection and coastal management ................................. 21
5.2Comparison between Dutch and Cape coasts ...................................................... 21
6References .................................................................................................................. 25
List of Tables:
Table 2-1: Relative sea-level trends for Cape Town. Stations are from the Permanent
Service for Mean Sea Level (PSMSL) data holdings (Mather et al., 2009) (adapted from
Goschen et al, 2009)............................................................................................................. 7
Table 2-2: Parameters and estimated maximum effects on still-water levels for the South
African coast (Theron and Rossouw, 2008) (adapted from Goschen et al, 2009).................. 8
Table 2-3: Significant Wave Height Statistics from Slangkop 1976-1988 (adapted from
Brundrit, 2009 – Phase 5A)................................................................................................... 8
Table 4-1: Cost of Damage in a Scenario 1 sea-level rise event (Cartwright, 2008 – Phase 3)
........................................................................................................................................... 17
Table 4-2: Indicative costs for different climate adaption options (Cartwright et al, 2008 –
Phase 4) ............................................................................................................................. 18
Table 4-3: Cost of damage to municipal property during storm event (RADAR, 2008) ........ 20
List of Figures:
Figure 1-1: Location of Cape Town on the world map ........................................................... 4
Figure 2-1: Cape Town districts ............................................................................................5
Figure 2-2: Satellite Image of central Cape Town (www.Geology.com)................................. 6
Figure 2-3: Topographical map of Cape Town centre (www.mapstudio.co.za)...................... 6
Figure 2-4: Section of Cape Town Naval chart (South African Navy Hydrographic Office) .... 7
Figure 2-5 Bathymetry around the Cape Peninsula down to a depth of 70m at 5m intervals.
(Brundrit et al, 2009 - Phase 5A)........................................................................................... 9
Figure 2-6: The exposure of the City of Cape Town to the worst case storms to be expected
( Brundrit, 2009 - Phase 5).................................................................................................. 10
Figure 2-7: Expensive real estate along Clifton beach (www.about.com) ............................ 11
Figure 3-1: Broad protection types along coast................................................................... 12
Figure 3-2: Cape Town Centre flooding (Cartwright et al, 2008 – Phase 3)......................... 14
Figure 3-3:A snap shot image (1:7,222) of the Strand area, depicting the three inundation
areas used in the GIS inundation model (Brundrit et al, 2009 – Phase 5A) ......................... 14
Figure 3-4: Photograph of a proposed upmarket development site on False Bay coast
(Cartwright, 2008 - Phase 3 report)..................................................................................... 15
Figure 3-5: Climate adaption options for Cape Town (Cartwright et al, 2008 - Phase 4)...... 16
Figure 3-6: Waves breaking on prime property at Glen Beach (lesterhein.blogspot.com).... 16
Figure 3-7: Waves overtopping the Sea Point Sea Wall (lesterhein.blogspot.com) ............. 16
Figure 4-1: Significant Wave Height during storm (Beckman, 2008).................................... 19
Figure 5-1: Cape Point (www.capepoint.co.za) ................................................................... 22
Figure 5-2: Land based nature reserves.............................................................................. 22
Figure 5-3: Marine protected areas ..................................................................................... 22
Figure 5-4: Economic activity along the coast ..................................................................... 23
Figure 5-5: Clifton beach (www.southafrica.to).................................................................... 24
Much of the world’s population is living along the coast. Climate change, along with the
corresponding rising sea levels, and population growth is putting much pressure on existing
coastal defences and could cause significant damage to unprotected coastlines.
There is a need to quantify the potential adaption measures and costs in terms of climate
adaption worldwide. Research is currently done about the impact of climate change on 136
port cities around the world (Linham et al 2010); this project is coordinated by Robert
Nicholls from Southampton University. Delft University of Technology, in cooperation with
Royal Haskoning, has been approached to research coastal defense unit costs in more
detail; with real costs from case studies relating to The Netherlands, Vietnam and New
Orleans projects. This report is an additional case study provided as an annexure to this
abovementioned coastal defence cost project report. It should be noted that this report only
gives an indication of costs related to coastal protection in Cape Town due to the limited
scope and timeframe that was available for this project.
The City of Cape Town Municipality (hereafter referred to as the City of Cape Town) has
experienced increasing coastal damage relating to more frequent and bigger storms and is
vulnerable to rising sea levels. The most significant hazards to the Cape Town coastline are
erosion and wave run-up during storm events. This leads to large economic risk and
damage, for both the City of Cape Town and private property owners, to infrastructure and
assets in proximity to the coast. This study is a brief review of relevant literature to give
indicative costs for climate change adaption in Cape Town. Information relating to the
damage caused by a recent storm, which took place in 2008, is provided along with an
estimate about economic risk to the City of Cape Town in event of a design storm.
Figure 1-1 gives the location of Cape Town on the Southern tip of Africa.
Figure 1-1: Location of Cape Town on the world map
The City of Cape Town Municipality administers approximately 307 km of coastline; which is
arguably its single greatest economic and social asset (Cartwright et al, 2008 – Phase 1).
Cape Town is the second most populous city in South Africa, with an estimated population of
approximately 3.5 million inhabitants (Statistics SA, 2007); and with an area of 2,450 km
2
,
which is the largest city area in South Africa. Figure 2.1 shows the 8 district municipalities
managed by the City of Cape Town.
Figure 2-1: Cape Town districts
Cape Town has a Mediterranean climate, with cold wet winters and dry hot summers, with
an annual ambient air temperature of 19°C (Wikipedia).
Cape Town is arguably the most popular tourist destination in South Africa; in 2006 foreign
tourist expenditure in the Western Cape totaled R19.80 billion (US$2.64 billion), while
False Bay
Table Bay
Cape Point
domestic tourism receipts were R1.50 billion (US$200 million). The forecast for 2008 for total
tourism revenue is R24 billion (US$3.2 billion) (Cartwright et al, 2008 - Phase 3). According
to the five year plan, Cape Town currently generates about 78% of the Gross Geographic
Product (GGP) of the Western Cape and some 12% of South Africa’s Gross Domestic
Product (GDP) (City of Cape Town Annual Report, 2009). The 2008 GGP for the City of
Cape Town was R165 billion (Based on 2006 figures of R123.6 billion) (Cartwright et al,
2008 - Phase 3). An exchange rate of R7.5 for $1 is used throughout the study.
Cape Town is a city interspersed with mountains, most notable Table Mountain and the
Cape Point mountain range. The topography is therefore very variable with some low lying
sandy areas, such as the Cape Flats (Figure 2-2), as well as maximum elevations in excess
of + 1,500 m MSL (Figure 2-3). The Cape Town coastline is extremely variable and differs
between mountain cliffs, rocky outcrops and pocket beaches as found along Cape Point to
gentle beaches with dunes behind them as found along False Bay and Table Bay (refer to
Figure 2-1 for locations). Generally it can be said that most of the Cape Town area is high
enough not to be prone to inundation after the breach of coastal defences, but rather that it
is vulnerable to erosion during storms (a situation which is exacerbated by the variation
between rocky and sandy coastline and occurrence of pocket beaches).
Figure 2-2: Satellite Image of central Cape Town (www.Geology.com)
Figure 2-3: Topographical map of Cape Town centre (www.mapstudio.co.za)
Cape Flats
The bathymetry of the ocean surrounding Cape Town is also highly variable, the general
trend is however that most of the exposed coastline has steep gradients as shown in Figure
2-4, which allows big waves to propagate close to the shore. Other areas are sheltered, such
as False Bay, and have shallower gradients. The gradient of the zone just offshore of Sea
Point can be approximated from Figure 2-4 as 20 meters divided by 600 meters, which gives
a slope of 1:30. This is a relatively steep slope; deep water can be found close to the shore
on many locations along the Cape Town coast.
Figure 2-4: Section of Cape Town Naval chart (South African Navy Hydrographic Office)
The maximum tidal variation between Lowest Astronomical Tide (LAT) and Highest
Astronomical Tide (HAT) is approximately 2 meters. The offset of Chart Datum (CD) relative
to Land Levelling Datum (LLD) is -0.843 metres at Simon’s Town Naval Harbour in False
Bay (www.satides.co.za), HAT is equal to LLD + 1.24 metres.
! "#
According to the IPCC report on sea level rise in South Africa (Goschen et al, 2009) the
greatest hazards to the South African coastline is that of short term events caused by
extreme storms and floods. The abovementioned report indicated relative sea-level trends
for Cape Town provided in Table 2-1.
Table 2-1: Relative sea-level trends for Cape Town. Stations are from the Permanent Service for Mean
Sea Level (PSMSL) data holdings (Mather et al., 2009) (adapted from Goschen et al, 2009)
Tide station Period of
Record
Years
of
record
Completeness
of record (%)
Observed annual
sea-level trend
using monthly data
(mm yr
-1
)
Observed annual
sea-level trend
using annual data
(mm yr
-1
)
Table Bay 1957-
1972 16 Insufficient data
Simons
Town 1957-
2007 51 78 +1.6 ± 0.2 +1.2 ± 0.5
-
20 m contour line
1.38 km
1.38 km
0.7 km
The maximum still water effects as recommended by Theron and Rossouw (2008) are given
in Table 2-2, it should be noted that the values in this table are mean values for the whole
South African coastline.
Table 2-2: Parameters and estimated maximum effects on still-water levels for the South African coast
(Theron and Rossouw, 2008) (adapted from Goschen et al, 2009)
Parameters and effects Elevations (m to mean sea level)
and setup (+ m)
Mean high water spring tide 1.0
Highest Astronomical Tide (HAT) 1.4
Severe wind set-up +0.5
Maximum hydrostatic set-up +0.4
Wave set-up +1.0
100 year sea-level rise +0.2 to +0.6 (say 0.4)
This can be compared with the overall monthly maximum deviation in sea level (without tidal
impact), in a recorded period of 30 years, which was recommended to be +0.4 metres in the
City of Cape Town Sea-Level Rise Risk Assessment (Cartwright et al, 2008 – Phase 1) and
is much smaller than the potential combined set-up of 0.9 metres recommended in Table 2-
2. The sea levels of LLD +1.54 m at a return period of 100 years and LLD + 1.63 m for a
return period of 500 years are extrapolations used in further studies by the City of Cape
Town (Cartwright et al, 2008 - Phase 1).
$ % "
A summary of the wave climatology for Cape Town as described in Phase 5 of the Sea Level
Rise risk assessment report (Brundrit et al, 2009) is given:
• A deep water wave recording site, Slangkop, situated 14 kilometres offshore in 170
metres deep water provided records for 12 years (1976-1988) (11424 records at 6
hourly intervals = 63% coverage).
• A median peak period of 12.4 seconds was measured for the wave date in Table 2-3.
Table 2-3: Significant Wave Height Statistics from Slangkop 1976-1988 (adapted from Brundrit, 2009 –
Phase 5A)
Significant wave height H
S
Metres
Median value 2.6
Value at a return period of 1 year 7.6
Value at a return period of 10 year 9.4
Value at a return period of 100 year 11.1
Figure 2-5 Bathymetry around the Cape Peninsula down to a depth of 70m at 5m intervals. (Brundrit et al,
2009 - Phase 5A)
The coastline is more exposed to extreme events from the South West as shown in to Figure
2-5. Wave information is summarized below (Cartwright et al, 2008):
• A big wave event is defined as one which has a significant wave height exceeding
6.5 metres for at least 6 hours (Van der Borsch, 2004).
• Thirty two big wave events were identified at Slangkop over the 21 year
measurement period (1983 to 2003).
• It should be noted that the distribution of these events are grouped and seem to
correspond to years that had persistently warmer sea surface temperatures.
• The average significant wave height within these 32 big wave events is 7.7 metres,
with standard deviation 1.0 metres, which can be compared with the value of the
significant wave height at a return period of one year of 7.6 metres, as given in Table
2-3.
• The average of the maximum individual wave heights within each big wave event is
12.7 metres, with a standard deviation of 1.8 metres, so that the events can certainly
be classed as big wave events.
• The overall maximum individual wave within these 32 big wave events reached 17.1
metres.
• There is a restricted directional spread, with 95% of the records taken within the big
wave events being from the south-west between 200 and 260 degrees.
• Big waves also occur from the South-East, but at somewhat lower chances of
occurrence.
The following scenario is assumed to by the present day worst case scenario for Cape
Town; the maximum sea levels that can be expected taking into consideration storm setup,
wave height and tides (rounded up to the 0.5 metres to fit the GIS system).
• a 2.5 metre increase in sheltered environments
• a 4.5 metre increase in exposed environments
• a 6.5 metre increase in very exposed environments
This scenario would see 25.1 km
2
covered by the sea (1 percent of the Cape Metro’s total
area of 2,499 km
2
), albeit for a short time (Cartwright et al, 2008 - Phase 1), as can be seen
in Figure 2-5. The analysis was also done for two other future scenarios, but would not be
considered in this report. It is assumed that Scenario 1 has a 95% chance of occurring in the
next 25 years (Cartwright et al, 2008 - Phase 3). Figure 2-6 gives an indication of the
elevation of vulnerable coastal areas. The areas in blue will be flooded in event of a total
storm surge of +2.5 metres (this includes wave and tidal impact); in red in event of a +4.5
metres storm surge (as could be expected in exposed environments according to Scenario
1) and orange the flooding in event of a storm surge of +6.5 metres all above LLD.
LLD+2.5m (sheltered environments)
LLD+4.5m (exposed environments)
LLD+6.5m (very exposed environments
Exposure to Worst Case Storms
Figure 2-6: The exposure of the City of Cape Town to the worst case storms to be expected ( Brundrit,
2009 - Phase 5)
These vulnerable areas are mostly built-up (with the exception of two estuaries) and are of
high economic value. It includes parts of the central business district of Cape Town and also
much of the most expensive housing in the city (such as housing along Clifton beach as
shown in Figure 2-7).
Figure 2-7: Expensive real estate along Clifton beach (www.about.com)
Figure 2-7 also gives an indication of the vulnerability of some of these developments that
are situated directly along the beach against the steeply inclined slope of Lion’s Head
Mountain.
&'
The City of Cape Town does not currently have generic coastal defence solutions
implemented along shore, but rather tailored solutions (where necessary) to accommodate
the variations of the coastline. Most of the coastline is not, in essence, protected by
artificially designed solutions, but rocky cliffs (such as along Chapman’s Peak and Cape
Point) and coastal dunes (e.g. along False Bay and Table Bay) provide natural protection. In
many instances the natural dune protection has however deteriorated due to encroaching
development and would need maintenance and potentially have to be expanded in future.
There are parts of the coast protected by sea walls such as the reclaimed area Sea Point
(which is also an old landfill site). The Port of Cape Town and V&A Waterfront leisure
development is protected by breakwaters. A wide variety of protection measure is needed for
Cape Town’s constantly changing coastline. Figure 3-1 shows the differing types of coastal
protection around the central part of the city. It again highlights the variability of the coastline
and the associated need for different protection measures.
Figure 3-1: Broad protection types along coast
A Coastal Act was passed in 2009 (Government Gazette), which aims to establish integrated
coastal and estuarine management by means of a legislative basis. It provides the base for
creating coastal ‘buffer zones’, in an attempt to stop inappropriate development
(Government Gazette, 2009). The current protection level for the coastline is estimated to
range between 1:20 and 1:200, but is not freely available or known for all areas.
It is apparent that the current coastal protection measures need to be studied in more detail
to provide integrated solutions for the whole coastline. To reach the abovementioned goal
the City of Cape Town has been proactive in developing its own Coastal Zone Strategy
(2003). This Coastal Zone Management Strategy was adopted, by the City of Cape Town,
Hard protection: Breakwaters and Dolosse
Hard protection: Vertical Sea Wall
Soft protection: Dunes and Beach
Sea
P
oint Sea Wall
with the intention to manage and safeguard the coast. Previously this coastal zone was
managed in a fragmented way by three different governmental agencies (Cartwright et al,
2008 - Phase 1) and was mainly reactive.
According to the Coastal Zone Management Strategy it offers a unique opportunity to
introduce a paradigm shift in coastal management practises (Coastal Zone Strategy, 2003):
• ‘A coordinated and integrated approach to coastal zone management from a
citywide perspective
• Recognition of the coastal zone as a distinct and unique management area
• Recognition of the coastal asset in terms of economic and social development
• The establishment of a multi-disciplinary coordinating coastal management
team
• Responsibility, accountability and action
• Centralised planning and budgeting around coastal issues
• Equitable access to our coast and its associated economic and social
opportunities
• Participative, open and transparent approaches to coastal zone management
• Creative, dynamic and new approaches to coastal zone management’
The City of Cape Town sees climate change and rising sea levels as an important part of its
future coastal zone management and has therefore embarked upon a thorough study of the
impacts of this on Cape Town titled ‘Global Climate Change and Adaption – A Sea-Level
Rise Risk Assessment’ . The study involves different phases of which the following has been
completed:
• Phase 1: Sea Level Rise Model (Brundrit, 2008)
• Phase 2: Risk and Impact Identification (Fairhurst, 2008)
• Phase 3: A Sea-Level Rise Risk Assessment for the City of Cape Town (Cartwright,
2008)
• Phase 4: Sea-Level Rise Adaption and Risk Mitigation (Cartwright et al, 2008)
• Phase 5A: Full investigation of alongshore features of vulnerability on the City of
Cape Town coastline, and their incorporation into the City of Cape Town Geographic
Information System (GIS) (Brundrit, 2009)
• Phase 5B: Sea-level rise vulnerability assessment and adaption options (Cartwright,
2009)
The aim of the Sea-Level Rise Risk Assessment Project (according to Phase 1 - 5) is to:
• Model the predicted sea-level changes in a range of scenario’s
• Model the form that those changes will take
• Understand the associated impacts on existing coastal systems, infrastructure and
property
• Provide guidance and implications to future coastal development (to be included in
the City’s Coastal Development Guidelines)
• Identify high risk areas
• Develop long-term mitigation measures
The primary objective of this study is therefore (according to Phase 1 - 5):
• To model and understand the ramifications of predicted sea-level rise and increased
storm events for the City of Cape Town, thereby providing information that may be
used for future planning, preparedness and risk mitigation.
The Sea-Level Risk Assessment Project identified vulnerable parts of the coastline. As much
economic activity is located along the coast the financial losses and risks in event of flooding
and storm damage would be very significant. Figure 3-1 shows the proposed impact a
Scenario 1 event could have on Cape Town’s central business district (CBD) and port.
Figure 3-2: Cape Town Centre flooding (Cartwright et al, 2008 – Phase 3)
The rise in water level is not necessarily such a big risk to the Port of Cape Town, but the
increase in storminess would most likely lead to increased downtime in port operations
which is linked to significant loss of potential income for the port. Figure 3-3 shows the low-
lying and generally unprotected Strand coast; which is situated on the eastern end of False
Bay. The sea wall along the beach road is insufficient protection against bigger storms. The
area is urban and contains housing and commercial facilities.
Figure 3-3:
A snap shot image (1:7,222) of the Strand area, depicting the three inundation areas used in
the GIS inundation model (Brundrit et al, 2009 – Phase 5A)
Figure 3-4 shows a proposed upmarket development site situated on False Bay coast; the
narrow dunes protecting this region and the corresponding exposure to sea level rise should
be noted. In some areas development has taken place almost up against the beach; the
road along the coast is a main transport hub and it is noticeably vulnerable to sea level rise.
Figure 3-4: Photograph of a proposed upmarket development site on False Bay coast (Cartwright, 2008 -
Phase 3 report)
The Cape Town coastline is very vulnerable to coastal erosion during storm events and
many of the climate adaption options are focused on this aspect. Selected climate adaption
options advised for the proactive coastal management of the Cape Town coastline
(Cartwright, 2008 - Phase 4) are shown in Figure 3-5.
Figure 3-5: Climate adaption options for Cape Town (Cartwright et al, 2008 - Phase 4)
It has become apparent to the City of Cape Town municipality that the current level of
coastal protection is not in all instances sufficient to handle the larger and more frequent
storms influenced by rising sea levels. Figure 3-6 and 3-7 were taken in August 2008 when
the biggest storm in 7 years hit Cape Town. Figure 3-6 shows the Sea Point sea wall which
is currently being restored; it is visible that the wall is not designed to withstand these bigger
storms.
Figure 3-6: Waves breaking on prime property at
Glen Beach (lesterhein.blogspot.com)
Figure 3-7: Waves overtopping the Sea Point
Sea Wall (lesterhein.blogspot.com)
("") *
Relevant literature relating to climate adaption cost estimates, potential damage costs and
actual damage costs for Cape Town are recapitulated in this section. All tabulated costs are
given in terms of 2008 values in South African Rand (ZAR) and United States Dollar (US$).
In Phase 3 and 4 of the City of Cape Town Sea-Level Rise Risk Assessment report
(Cartwright et al, 2008) an attempt is made to quantify the opportunity costs in event of
environmental damage. The following paragraphs briefly highlight some of the findings in
abovementioned reports for a Scenario 1 event.
Cape Town is associated with its beautiful beaches and a Scenario 1 Sea-Level event would
presumably lead to foregone tourism revenue (it is assumed that tourism will decrease by 3
percent during the year of the event). This is related to the erosion of beaches such as
Camps Bay, Clifton and Llundudno which would decrease their aesthetic appeal as was
illustrated in the tourism losses experienced after an extreme storm took place during 2007
in Durban on South Africa’s east coast (Cartwright et al – Phase 3; Mather et al, 2007b).
The cost of replacing public infrastructure (which falls under the City of Cape Town’s
authority – this excludes the Port of Cape Town which is the responsibility of national
government) is a financial risk to the municipality. Storm water and electrical distribution
infrastructure and municipal transport lines are assumed to be some of the most affected
services. It is assumed that 1.5 percent of the city’s storm water infrastructure would need to
be repaired in a Scenario 1 event. The estimated cost of road replacement is R900 million
and should be compared to the annual road maintenance budget for the City of Cape Town,
which is approximately R200 million (Cartwright et al, 2008 - Phase 3). The estimation is that
1 percent if the above surface energy infrastructure will need repair or replacement. A
cumulative risk cost is estimated for the City of Cape Town using the occurrence
probabilities for the event during the next 25 years, it should be noted that this is an extreme
value as the assumption is made that flooding occurs all along the coastline whereas it is
generally more localized. The values therefore represent the cumulative risk and coasts over
a 25 year period. The cost of damage according to Phase 3 (Cartwright et al, 2008) is
summarized in Table 4-1.
Table 4-1: Cost of Damage in a Scenario 1 sea-level rise event (2008 values) (Cartwright, 2008 – Phase 3)
!
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The Sea Point seawall is currently being repaired. According to Phase 3 (Cartwright et al,
2008) provisional estimates given to the city indicate that at least R 12.6 million (US$ 1.68
million) will be required for immediate repair and an additional R250 000 (US$ 33 300) per
annum should be budgeted for maintenance. The Sea Point sea wall dimensions can be
approximated as a length of 4.8 kilometres and a height of 6 metres above the mainly rocky
shore.
The different adaption options presented in section 3 above (Figure 3-5) were also
compared in terms of their relative implementation cost and the suitability of their
implementation. Table 4-2 gives a summary of the available cost information about climate
adaption.
Table 4-2: Indicative costs for different climate adaption options (Cartwright et al, 2008 – Phase 4)
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It should be noted that the cost given for managed retreat in this instance only includes the
weighted average cost of the property which will be lost; the real cost will be higher and
include compensation to property owners, lost public infrastructure and loss of real estate.
The unit cost for sea walls are dependent upon the height of the wall, the design of the cross
section and the materials used; however the unit cost provided in Table 4-2 was not defined
in terms of height or other factors in Sea Level Rise Risk Assessment (Cartwright et al, 2008
– Phase 4) and therefore is given as a wide range of possible values with a potential
difference of a factor 10 as could easily be the case in practice. Two costs for beach
nourishment are given; one is sourced from the Sea Level Rise Risk Assessment (Cartwright
et al, 2008) for Cape Town and is in cost per meter, whereas the other is from Linham et al
(2010) and in cubic metres. Due to the variability of beach profiles, widths and lengths in
Cape Town it is not really feasible to estimate a generic nourishment volume in cubic metres
per metre and the value provided in Linham et al (2010) is favored as a unit cost. As seen in
Table 4-2 cost information is not freely available and it is difficult to source accurate unit cost
values for local projects. This makes it difficult to budget for future adaption. In this instance
the tendering process for government projects is very competitive and consultants are
therefore not eager to provide costing information. It is recommended that the City of Cape
Town should build up a costing database relating to coastal protection projects (if it does not
already exist).
+ "
Cape Town was affected by a ‘super storm’ over the weekend of the 30
th
– 31
st
of
August 2008. This storm was associated with the passage of an intense mid-latitude
cold front. Violent North-Westerly winds of 50 km/h were experienced, with gusts of 80
km/h, which caused a storm surge by piling up the water against the coast. These
factors contributed to an increase in mean sea level of over 5 metres; which had a
damaging impact on the coastline. Sea swell and waves in excess of 10 metres were
experienced as shown in Figure 4-1; this caused major damage to property and altered
the beach profiles. Heavy rainfall was experienced during the storm. (Beckman, 2008)
Figure 4-1: Significant Wave Height during storm (Beckman, 2008)
#
It is estimated that most of the damage that occurred during the storm was to formalized
private and commercial property and referred to insurers. Unfortunately this information is
confidential and has not been made available by insurance companies. Much infrastructural
damage transpired along the coastline; including damage to retaining walls, buildings,
transport and parking areas etc. The total estimated damage to coastal facilities and
structures is valued at roughly R4 937 500 (US$ 655 300). This could be compared to an
approximate damage estimate to municipal infrastructure at eThekweni Municipality
(Durban) of R100 million (US$13.4 million) during a low pressure storm system, which
coincided with the 18.6 year highest tide, on 19 and 20 March 2007 (Mather, 2007b) (This
cost is given in 2007 values). Table 4–3 gives a summary of the estimated damage cost of
the August 2008 storm in Cape Town to the municipality.
Table 4-3: Cost of damage to municipal property during storm event (RADAR, 2008)
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The cost of storm damage is potentially very significant in Cape Town as seen in Table 4-3.
This indicates that future coastal zone management should focus on protecting the coast
and minimizing the damage during storm events; which is also a goal of the City of Cape
Town municipality. The extreme storm experienced in KwaZulu-Natal (in South Africa) during
March 2007 showed that areas which were either only sandy or only rocky were generally
more resilient to the storm, whereas mixed coastlines of rock and sand (such as much of the
Cape Town coastline), especially pocket beaches, were severely impacted (Mather, 2007a;
Goschen et al, 2009). Extensive damage was incurred during the extreme storm in KwaZulu-
Natal and the statement above indicates that Cape Town could be potentially be even more
vulnerable due to the variable nature of the coastline.
!
!
Cape Town has a long and variable coastline. Much of the coastline has also been
encroached with development; unwisely so in some instances. This means that adaption will
be difficult and a diverse mix of solutions would be needed. A generic solution for coastal
protection cannot in this instance be formulated for the whole coastline. This makes the
adaption process much more expensive and time consuming.
Currently there is no specified protection level or recommended hydraulic boundary
conditions for building along the coast. There has however been much work done by local
and national government in terms of coastal policies and the protection of the coast. It can
be said that the City of Cape Town municipality is taking the risk of climate change very
seriously and that they are proactively looking at the issue.
! ,)
To illustrate the variability of the impact of climate change on coastlines around the world a
brief comparison is made between the Dutch and Cape Town coasts. As introduction it can
be said that more than one-fifth of the Netherlands is situated below sea level and is
therefore much more vulnerable to the sea than Cape Town is; coastal defence is therefore
a case of national safety and taken much more seriously in The Netherlands than in Cape
Town. The main risk in The Netherlands is that a breach of the coastal defences could lead
to flooding of the hinterland, whereas the main risk in Cape Town is that of erosion and short
term flooding during storm events.
The Dutch coast is a low-lying deltaic coast (Hillen et al, 2010) and generally sandy. It can
be separated in three generic sections; Zeeland in the south consists of islands, river mouths
and estuaries; the Holland coast in the middle; and the Wadden Sea coast with a big tidal
basin and barrier islands in the north. The coastline is sandy throughout and is in most
instances protected by dunes, with the exception of some sections sea dike. The estuaries
and tidal basin require more intervention and this led to the building of storm surge barriers
such as the Oosterscheldt and Maestlandkering. The generic nature of the Dutch coast
makes it simpler to develop standard design solutions such as dune protection, which can be
used along most of the coast with only slight adaption’s necessary for the specific location.
Coastal protection costs would therefore also be easier to estimate.
In comparison the Cape Town coastline is extremely variable. Some areas such as False
Bay have gentle sandy beaches and dune protection solutions similar to that used in the
Netherlands is suitable here. However large parts of the Cape Town coastline are rocky and
mountainous. Figure 5-1 of Cape Point shows rocky outcrops with a narrow pocket beach in
between. Other areas are protected by sea walls, revetments or breakwaters as described in
Section 3.
Figure 5-1: Cape Point (www.capepoint.co.za)
The Cape Town coast is also very rich in ecological and marine biodiversity. It is one of only
three cities in the world classified as urban biodiversity hotspots. It is also one of the smallest
of the 25 biodiversity hotspots in the world, which means that it is one of the places in the
world with the richest and most threatened plant and animal life (Green Map of Cape Town,
2009). The warm Agulhas current that sweeps down the east coast and the cold Agulhas
that flows north along the west coast meet at Cape Town, which leads to rich biodiversity in
marine life (Beaches: A diversity of coastal treasures, 2009) . There are various marine and
land based nature reserves in the city limits (where no development is allowed) and all new
development in the coastal zone now requires an Environmental Impact Assessment (this
would also be required for coastal protection work). Figure 5-2 (Green map of Cape Town,
2009) and 5-3 (City of Cape Town Beaches: A diversity of coastal treasures, 2009) shows
the land and marine nature reserves within the city limits.
Figure 5-2: Land based nature reserves
Figure 5-3: Marine protected areas
The diversity in terrain and ecosystem along the Cape Town coast complicate the
development and implementation of coastal protection solutions, it is generally necessary to
develop a new design solution for each part of the coast. It is also difficult to determine unit
costs for coastal protection in Cape Town due to a big range in solutions and costs (as well
as the fact that the available information is limited).
In Cape Town much of the coastline is a focus for economic activity. This is not traditionally
the case in the Netherlands where the economic hotspots were generally situated more
inland (although connected to the coast by rivers, estuaries and channels e.g. Rotterdam
and Amsterdam). Population growth and economic expansion in The Netherlands have
however led to development encroaching upon the coast, although the coastal protection
legislation of the Netherlands still limits the development. Main highways in the Holland
region are generally not situated along the coast as can be seen in many coastal cities,
including Cape Town. In Cape Town development started along the coast (as a Dutch
colony) and expanded inland, the harbour was one of the first areas developed and
businesses and industry was developed around it.
Cape Town’s Central Business District (CBD) is situated in close proximity to the sea and
the coast is a hotspot of economic activity and investment as Figure 5-3 illustrates. The
World Cup stadium cost R4.4 billion (or approximately US $600 million) to build and was
completed in 2010 (Wikipedia). The V&A Waterfront shopping mall and entertainment area is
arguably the most visited tourist destination in South Africa; Sol Kerzner’s One and Only
Hotel was completed in 2009 and cost approximately R1 billion (US$134 million) to build
(The Property Magazine) . The Port of Cape Town handled 774000 TEU’s in the 2008/2009
financial year (Transnet). In Figure 5-4 and 5-2 it is also visible that space for further
development of the city centre is restricted by the sea and Port of Cape Town, as well as by
the surrounding Table Mountain nature reserve.
Figure 5-4: Economic activity along the coast
The Cape Town coast is a very valuable tourist attraction and many businesses are catering
for the foreign tourist market. It is famous for its beautiful beaches (such as Clifton shown in
Figure 5-5) and nature reserves. If the beaches are damaged and eroded due to a big storm
it could affect their attractiveness to tourists. Tourism in the Netherlands is dominated by
World Cup Stadium
Port of Cape Town
V&A Waterfront
One and Only Hotel
CBD
visitors to Amsterdam, Keukenhof and cultural locations (such as dikes and windmills);
beaches are not such an important attraction.
Figure 5-5: Clifton beach (www.southafrica.to)
In The Netherlands the geography and shallow water depths of the North Sea basin leads to
very high storm surge, the design storm surge level is therefore 6 meters, whereas in Cape
Town the design surge is lower than a meter. Cape Town can however experience bigger
waves due to the deep water close to shore and thus wave penetration are not as restricted
by water depth as in the Netherlands.
A very common protection measure in The Netherlands is beach nourishment. This is a
relatively uncomplicated exercise in The Netherlands due to the availability of dredgers and
also potential for offshore sand mining close to site. This solution is much more difficult in
Cape Town, where offshore sand mining is much more expensive and environmentally
damaging.
The level of available information about shoreline movement and hydraulic records (wave,
wind, water level etc) is very high and of a long duration in The Netherlands. Most
information is freely available and hydraulic design conditions have been established by a
governmental organization for the whole Dutch coastline. In Cape Town there is a significant
lack of freely available information about coastal protection, hydraulic records and shoreline
movement.
To conclude it is apparent that the Dutch and the Cape coasts are very different and that this
also necessitates different protection measures. Adapting coastlines around the world would
also require site specific solutions and the cost of solutions would be influenced by local
conditions such as the cost of labour.
$ #
Beckman, T. (2008) August 30
th
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• (2009) Green map of Cape Town; www.capetowngreenmap.co.za
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• www.Geology.com: Satellite image of Cape Town
• www.about.com: Clifton beach estates
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• lesterhein.blogspot.com: Storm photos
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port cities: Draft report
Mather, A. (2007a) Coastal Erosion and Sea-Level Rise: Are Municipalities ready for this?.
eThekekweni Municipality
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KwaZulu-Natal Minister of Agricultural and Environmental Affairs . eThekweni Municipality
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Africa. Report prepared for the eThekwini Municipality
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