About this book
Zur Kategorie Neu eingetroffen. Zur Kategorie Belletristik. Zur Kategorie Ratgeber. Zur Kategorie Nonbooks. This book explores the benefits of using risk analysis techniques in the evaluation of flood protection structures, and examines the results of the environmental impact assessment for selected planned flood protection projects.
Using Risk Analysis for Flood Protection Assessment | leuhosarsero.tk
The objective of the book is to propose a methodology for environmental impact assessment in water management. In more detail, flood mitigation measures are investigated with the aim of selecting the best option for the approval process. Depth-damage curves are used for flood risk assessments in many countries de Moel et al. Therefore, depth-damage curves from the DamageScanner model Klijn et al.
For each aggregated land use class, the associated depth-damage curve is applied to calculate the damage as a percentage of the maximum value.
According to the depth-damage curves, maximum damage is assumed to occur at a water depth of 5 metres.. Using the EAD as input, we apply a CBA to determine whether flood protection by dike infrastructure is economically attractive, i.
The function for calculating the NPV is shown in equation 1. We calculate the NPV for different protection standards ps. The protection standards, which correspond to the flood return periods, for riverine protection are 5, 10, 25, 50, , , , and years. For coastal protection, the protection standards are 10, , and years. Benefits for each protection standard ps are represented by the sum of the EADr , for each time-step t , over the total dike lifespan of years T.
Benefits are time-dependent because flood risk changes due to climate change and socio-economic developments.
Note that for river floods, the required dike height for each flood return period is calculated using the water volume for a certain return period, which implies that the dike should be high enough to keep the water volume for the given return period in the protected river channel. Furthermore, dike length and dike height are determined for each cell separately for both river and coastal dikes. For river dikes the dike length is two times the river length, as both riverbanks need to be protected. As there is often a floodplain between the river and the dike, to allow room for the river and to reduce the required dike height, it is assumed that the floodplain width is two times the current river width.
In supplementary material S1 we show the sensitivity of the results to this parameter. Figure 5 shows the location of the envisaged dikes. The investment costs I 0 applied here are 2.
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The investment costs were estimated as follows: the estimated costs for constructing dikes in the US Bos, were converted to an estimate applicable to rural areas i. Maintenance costs were estimated by correcting estimates of dike maintenance costs in low- and middle-income countries Mai et al. The lifespan of the dike infrastructure is set at years Aerts and Botzen, Left: Location of the envisaged river flood protection infrastructure red , and the modelled river one in yr flood extent under current climate blue.
Right: Location of envisaged coastal flood protection infrastructure red , and the modelled one in yr coastal flood extent under current climate blue.. Future benefits and costs were discounted using a social discount rate r to reflect the opportunity costs of public capital. Supplementary material S1 shows the sensitivity of the results to using a higher social discount rate..
As shown by the flood extents in Figure 5 , the modelled flood extent for river flooding is considerably larger than that of coastal flooding. Table III presents the modelled extent in km 2 of different return periods for the state of Tabasco.
While hurricanes are common in the Gulf of Mexico, they do not produce major storm surges along the coast of Tabasco EHS-GA, , and the modelled extent for coastal floods is thus relatively small km 2 compared with the areas that can be inundated by river flooding km 2.
Although hurricanes contribute to storm surges, their main impact in Tabasco is through heavy rainfall and consequent river flooding. This is aggravated due to deforestation in the upper catchment areas, a shallow topographical gradient, and poor flood management EHS-GA, Table III shows that river floods can inundate a sizeable area of the state of Tabasco, between and km 2.
These figures reflect the number of people located within the modelled flood zone. For river floods, the number of people at risk rises to for a one in yr flood. In contrast, 23 people live in areas that can be inundated by the one in yr coastal flood. In reality, the number of people that are affected by either coastal or river floods can be far greater, as a consequence of damaged infrastructure and impeded access to livelihood needs. Note that the resampled elevation maps used to extrapolate coastal floods can only account for 1-metre differences. Since the surge heights for the one in yr flood and 1 in yr flood are within one metre of each other, the modelled area and population at risk are similar for both..
The area and population at risk of river flooding under current climate conditions..
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The difference in flood extents and depths of river and coastal floods also causes them to have significantly different impacts in terms of EAD. For current climate, the model results show an EAD of 0. While these values seem high, they are close to the reported damages in the period , when Tabasco was flooded by river floods on a yearly basis with a total damage of roughly five billion USD, as shown in Table I.
This is equal to an average yearly damage of approximately one billion USD over this period, which is of the same order of magnitude as our model predictions.. Table IV shows that the EAD of river floods for Tabasco is approximately four times higher than the EAD for coastal floods, under the assumption of current climate conditions. In the low-SLR scenario, the EAD of coastal floods will rise to be six times higher in than under the assumption of a static sea level. For river floods, the RCP2. Interestingly, the RCP8.
While it is expected that global precipitation will increase with increased global mean temperature IPCC, , these changes are expected to exhibit substantial spatial variation; some regions will experience increases, while other regions will experience decreases or no significant changes at all. Although there is no specific data available for Tabasco, several models show that Mexico may on average experience drying IDB, The two considered climate scenarios, which capture the range of extremes of a much wetter RCP2.
It is important to note that while the EAD is based on the simulated damages per return period, the value itself does not indicate that these damages will actually occur from year to year, due to the variability of flood disasters in practice. The EAD is instead specifically useful in CBA for determining economically efficient adaptation strategies, as it translates the uncertainty of low-probability flood events into yearly monetary terms Eq.
The current scenario shows the results for no change in climate conditions. Furthermore, the results in Table V show that raising protection standards to 50 years yields the highest NPV, which indicates that this standard is the most economically desirable. Results of CBA for different river flood protection standards, for different scenarios of climate conditions. Because the assumption of static flooding conditions is unlikely considering climate change, the CBA results are also presented for climate change under RCP2.
The slightly wetter climate projected under scenario RCP8. Nevertheless, Table V shows that increasing riverine protection standards is economically desirable for all protection standards under future climate conditions. The results for the RCP2.
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Moreover, the results for the climate change scenarios again show a significant reduction in the EAD for the protection standards of 10 and 25 years, indicating that there is much to gain from relatively small investments.. It is important to note that while both climate change scenarios return the same optimum protection level of years, the actual height to build the flood protection infrastructure differs for each scenario.
A yr protection standard under the RCP2. Table VI presents the CBA results for different protection standards for coastal flooding, under different assumptions of climate change. Since the EAD is significantly smaller than for river floods, so too is the EAD that can be reduced by increasing coastal protection standards.
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However, as shown by Figure 5 , the total length of the dikes is also significantly lower, and therefore so are investment costs. Raising protection standards from to years does not significantly reduce EAD. For coastal protection standards, each dollar invested would yield 4. The NPV is highest for raising protection standards to yrs, although it is close to the NPV of protecting against the one in yr flood..
Results of CBA for different coastal protection standards under different scenarios. While it is already economically attractive to raise coastal protection standards in Tabasco under current climate conditions, it becomes increasingly attractive if SLR is included.