Failure to consider the costs of adaptation strategies can be seen
by decision makers as a barrier to implementing coastal protection measures.
In order to validate adaptation strategies to sea-level rise in the form of
coastal protection, a consistent and repeatable assessment of the costs is
necessary. This paper significantly extends current knowledge on cost
estimates by developing – and implementing using real coastal dike data –
probabilistic functions of dike costs. Data from Canada and the Netherlands
are analysed and related to published studies from the US, UK, and Vietnam in
order to provide a reproducible estimate of typical sea dike costs and their
uncertainty. We plot the costs divided by dike length as a function of height
and test four different regression models. Our analysis shows that a linear
function without intercept is sufficient to model the costs, i.e. fixed
costs and higher-order contributions such as that due to the volume of core
fill material are less significant. We also characterise the spread around
the regression models which represents an uncertainty stemming from factors
beyond dike length and height. Drawing an analogy with project cost overruns,
we employ log-normal distributions and calculate that the range between
Sea-level rise represents a foreseeable consequence of climate change and
there is considerable interest in comparing coastal flood damage with
adaptation costs
In order to estimate costs and benefits of adaptation to sea-level rise
While the climate impact and adaptation research community has made progress
in assessing the categories (i)–(iii), the construction costs of protection
measures (category iv) are poorly reported in the literature. These are
considered an engineering problem yet are also of utmost importance for
decision makers in order to assess the scale of the investment that is
required to provide protection and is achievable for the resources
available. Failure to consider the costs of strategies can invalidate, or at
least expose as impractical, recommendations from research studies. However,
engineers hesitate to provide general and transferable costs. Academic
literature is lacking “real-life” auditable cost information on adaptation
measures
One way to investigate construction costs is to study similar dikes that were
planned or constructed in the past. Using historic construction costs is
referred to as the elemental costs projection approach
Most authors studying adaptation to sea-level rise and adjunctive costs refer
to
Many of the above-mentioned studies use “unit costs”, i.e. the dike costs can be expressed per metre height. This, however, implies the assumption that there is a linear relation without fixed costs – an assumption that to our knowledge has not been supported quantitatively so far. In addition, uncertainty is at most quantified in terms of a range, i.e. some upper or lower values. This paper significantly extends these approaches by developing probabilistic functions of dike costs and implementing them using real coastal dike data.
In order to provide a
Second, what is the range of uncertainty that needs to be considered?
Although our findings are related to sea dikes, our research approach and
determination of uncertainty is potentially applicable and transferable to
other adaptation measures. In the research on climate change adaptation, the
constraints related to quantifying coastal protection costs listed above
represent an
In order to quantify the uncertainty of the dike construction costs, we draw
a parallel with project cost overruns. Construction projects usually exhibit
a difference between forecasted and actual construction costs
We base our main analysis on two data sources, namely
Estimated costs to protect Vancouver and neighbouring municipalities against
sea-level rise by 2100 are provided by
The costs presented in the Canadian study are referred to as a “class D
estimate”
Table 4.3A and B in
As detailed in Sect.
The Dutch report
Tables G and K in
As detailed in Sect.
In the following we fit regressions to the data, quantify the uncertainty, and compare our results with previously published estimates.
Plot of dike costs versus crest height for all dikes with a linear
fit without intercept, LWI (Eq.
In Fig.
In order to find a suitable model for typical costs we test four regressions,
namely (i) linear without intercept (LWI), (ii) linear polynomial (LP),
(iii) quadratic polynomial (QP), and (iv) power law (PL):
Equation (
In Fig.
Fit parameters according to Eq. (
In Table
The regressions for the Netherlands data are shown in
Fig.
While the regressions characterise the typical relation between dike height
and costs, next we want to study the spread around the fits. These deviations
of individual dikes are due to site-specific properties and design features
that go beyond the height and length and are usually unavailable. Therefore,
drawing the analogy with cost overruns, we employ log-normal distributions
Accordingly, we analyse the residuals of the fits as an estimate of the uncertainty.
The residuals were calculated as the ratio of fitted to observed values.
Then we fit log-normal probability distributions:
Two features support the choice of the log-normal distribution in this context. First, the log-normal distribution by definition excludes negative values. Second, the statistical spread is relative (for the same reason). Instead of a fixed uncertainty e.g. in EUR, it is defined as a fraction, or percentage, which is plausible since bigger projects typically have larger absolute uncertainty.
Spread of dike costs and estimated uncertainty. The dike costs are
shown together with the linear regressions without intercept,
Eq. (
For the Canadian and the Netherlands data, the estimated uncertainties are
displayed together with the LWI regressions in
Fig.
In the log–log scale (insets of Fig.
The Canadian data also include information about whether the dikes are
completely new or existing dikes are to be raised. In addition, the
land use in terms of urban/rural is specified, which strongly affects the
land price (see Sect.
GDP per capita, purchasing power parity (PPP) GDP per capita, and
mean exchange rates (
To compare our results with results from
The easiest way of adjusting for different currencies would be to use the
exchange rates. However, this does not take into account differences in
purchasing power. Considering these, the exchange rates have to be adjusted.
To do so, one method, used for example by the World Bank, is to adjust the exchange
rate of a currency
For the data from
Comparison of our results with data from different studies and
countries in terms of unit cost estimates for raising dikes, namely
We also include results for Great Britain by using the dimensions of the
dikes designed in the Canadian study to parameterise the calculation tool
developed for the Environment Agency
In Fig.
For both coastal protection projects, i.e. in Canada and the Netherlands, it
is sufficient to express the typical costs of dikes per height and length,
which is compatible with assumptions made in previous publications, e.g. in
The uncertainty considered here stems from a lack of knowledge, i.e. by
studying the costs only as a function of length and height, as we did not
have more detailed information on the local conditions and requirements of
the dikes available (although we assume that the authors of the reports did
have greater knowledge). Hence, we borrow the concept of cost overruns to
characterise the uncertainty of dike constructions. It is worth noting that
erected constructions may be affected by real cost overruns (the
original Canadian study included 50 % contingency), which increase both the
overall costs and the spread. Thus, in particular with regard to uncertainty,
our results are probably only lower estimates. Another aspect to be
considered is that we assume all dikes to have equal probability, i.e. each
dot in Fig.
We also want to discuss another aspect that comes into play: when the total
costs of an ensemble of dikes are aggregated, e.g. according to
The transfer of our findings and conclusions to other countries needs to be done with caution. Although plausible, we have no proof that the analogous parameters and consequent conclusions hold true in other countries. In particular, it cannot be excluded that fixed costs could represent a significant contribution in countries with weaker tradition in coastal protection or in countries that so far have not been threatened by sea-level rise. Similar arguments could also apply to the unit costs. Further research is necessary to better understand the unit costs so that they can be transferred to other countries and circumstances.
In the context of riverine floods, the lack of good-quality cost estimates
has hampered progress in the advance of large-scale flood risk modelling.
There is an urgent need for data on the location of dikes as well as their
costs and uncertainty
Comparing our estimates with the figures provided in the literature, we find
that the costs differ more between the countries than between land uses.
Nevertheless, within countries the differences due to land uses are
pronounced and, as expected, urban dikes tend to be more costly than rural
ones. However, when comparing such cost estimates it is crucial to note which
components are actually included in the figures. While in the Canadian report
Costs of operation and maintenance are another complication. Such costs
depend on frequency of inspections, annual maintenance requirements, and
long-term intermittent maintenance activities
To conclude, this study gives decision makers an order of magnitude on the protection costs which can remove potential barriers to designing and implementing adaptation strategies in other countries. Future research may focus on the creation of a “best practice” approach to understand how potential impacts are accounted for and to deliver to decision makers ways in which climate adaptation options such as sea dikes can be understood and measured, in terms of both investment needed economically and in reducing risks of flooding and reduced damage costs.
The underyling research data are referenced in the papers (de Grave and Baase, 2011; Delcan Corporation, 2012; Pettit and Robinson, 2012). The resulting data are given in Table 1.
The total costs (from Table 4.2 in Structural flood protection/embankment consists of 9 % of total costs.
For a dike of length Site preparation: clearing and removal of topsoil (costs Core material: supplying and installing the dike material (costs Rip-rap: stone protection for the water side of the dike (costs Surface restoration: construction of a typical asphalt road in case there is already a road at the site; this applies to 5/36 reaches (costs Utility relocation, pump stations, and flood boxes consist of 4 % of total
costs.
It was assumed that dike construction will include 25 % extra in urban areas and 5 % for rural areas for utility relocation. Upgrades of existing pump stations apply to 16/36 reaches, with an estimated unit cost of CAD 2.5 million. Adjustment of drainage behind the dike and small pump station installation applies to 18/36 reaches, with an estimated unit cost of CAD 0.5 million. Property acquisition consists of 17 % of total costs.
The area of property to be acquired is determined by the footprint, i.e.
costs Agricultural: 3 % of total costs, 9/36 reaches, 86 % of total area, estimated unit cost of CAD 22 m Residential: 6 % of total costs, 7/36 reaches, 4 % of total area, estimated unit cost of CAD 850 m Commercial/industrial: 8 % of total costs, 11/36 reaches, 11 % of total area, estimated unit cost of CAD 400 m Seismic resilience (vibro-replacement, deep soil mixing, toe berm)
consists of 34 % of total costs. Because the Vancouver area is seismically active, it is necessary to make dikes seismically resilient. Depending on the soil profile at the dike location
vibro-replacement, deep soil mixing or installing a toe berm is necessary.
Vibro-replacement: 10/36 reaches, with an estimated unit cost of CAD 22 m Deep soil mixing: 3/36 reaches, with an estimated unit cost of CAD 250 m Toe berm: 10/36 reaches. Environmental compensation consists of 1 % of total costs and 4/36 reaches, with an estimated unit cost of CAD 250 m Site investigation, project management, and engineering (15 % on top of previous
items) consist of 2 % of total costs. Contingency (50 % on top of all previous items) consists of 33 % of total
costs. exclude the following reaches: nos. 4 (floodwall), 5 (flood proofing, no information), 10 (barrier), 16 (double dike), 17 (flood proofing, no information), 23 (retreat), 27 (barrier), 28 (flood proofing, no information); disregard deep soil mixing of reaches 7, 8, and 22; and disregard 50 % contingency on top of the total costs.
Prior to beginning the analysis, we perform a few steps:
This leads to a total of 28 reaches being analysed.
The dike raising costs of the Dutch study are based on a system of cost functions. To obtain the cost function for one dike reach there are eight calculation steps taken into account:
Identify the needed dike height raising by modelling the hydraulic strain for a given dike height and return level interval. Process the information about the current and the required dike profile to determine the needed ground and construction measures. This step takes into account:
the dike height of the initial situation, the benching height of the initial situation if there is benching on the land side, the distance between the outer dike crest and the dike foot on the land side, the required raising of the base body of the dike (corresponding to the required raising of the dike crest including an additional raising for settling and compaction), broadening of the dike base for increasing macrostability,
and broadening of the dike base for piping. Determine the range of ground and construction measures according to a four step expulsion list with the following combinations of measures:
complete solution with exclusively ground measures, raising and fortification of the dike body with a combination of ground measures and one construction measure on the dike toes on the land side, dike raising in the ground and steepening of the (inside) embankment on one side in combination with one construction measure within the dike
body, and dike raising in the ground and steepening of both dike embankments in combination with a cofferdam construction within the dike body. According to the selected combination of measures, the new dike profile, the
type and extent of the required construction measures, the additional
footprint of the dike, the direct ground work and construction costs per unit
of length, the length of the dike section to which the measures are applied,
the total construction costs, and the additional costs for administration and
maintenance are calculated. Calculate the costs needed for dike reaches with special conditions. These special conditions consist of the construction of a cofferdam.
The costs for this is estimated using both the horizontal and vertical length, the height and a standard cost
function. Estimate the costs needed for the adjustment of infrastructure. This applies if there is an existing road or other type of traffic
infrastructure which has to be reallocated. This also applies if there are crossroads or railways located above the dike which interfere
with the raising of the dike. This may require the construction of a new dike section. Identify costs for purchase of land. To estimate this kind of costs there are four cases which are being differentiated,
namely built-up area, non built-up area, urban, and rural. For the two categories built-up and urban the land acquisition costs are considered
to be high and for non built-up and rural comparatively low. Determine costs for countryside and environment compensation measures. If a dike reach crosses a nature reserve or an area of
special scenic importance, it is necessary to acquire land create appropriate compensation measures. Estimate the volume of the total investment costs and additional annual costs for administration and maintenance. The total
investment costs are formed by summing up the costs (including their administration and maintenance costs) of the previous seven steps.
Based on this, the total administration and maintenance costs are defined as percentage of the total investment costs.
In Table B1 we provide our estimated unit costs in comparison with values found in the literature. See also Fig. 3.
Comparison of different cost estimations for raising a dike of length 1 km for a height of 1 m for different land uses and different dike types. Land use and dike types are labelled here when available. All values have been converted into 2012 Euros to make them comparable. See also Figure 3 in the main text.
The authors declare that they have no conflict of interest.
We thank H. Costa, G. Floater, R. J. Meijer, and Boris F. Prahl for useful discussions, M. Olonscheck for her translation skills, and C. J. Hewett for help with the manuscript. The research leading to these results has received funding from the European Community's Seventh Framework Programme under grant agreement no. 308497 (Project RAMSES). The publication of this article was funded by the Open Access Fund of the Leibniz Association.Edited by: B. Merz Reviewed by: two anonymous referees