Flood Protection Strategies Research Articles

Evaluating the feasibility of coastal protection scenarios on a city scale across plausible pathways scenarios for both sea level rise and urban development

Coastal flood risk accelerates rapidly due to rising sea levels and urban expansion in low-lying areas. Many strategies based on the widespread application of hard protection have been developed. However, the implementation of such measures has raised concerns due to their environmental impact, high costs, and a potential increase in exposure.This study focuses on the economic implications of coastal flood protection at the local level, examining impacts on small to medium-sized cities, which reflects many coastal communities around the world. We introduce a framework for assessing the economic burden or benefit of flood protection strategies on local communities and municipalities. We derive standardized values for protection costs, flood risk, and socioeconomic development for typical coastal topologies, i.e., the data usually used for cost-benefit analyses of coastal protection.Based on two illustrative examples of coastal cities in different topographies, we demonstrate that cost-effective protection strategies can lead to lock-in situations because their implementation cost likely exceeds local willingness to pay, and we argue that this risk needs to be considered when designing flood adaptation pathways.

Assessing Multidimensional Vulnerability of Rural Areas to Flooding: An Index-Based Approach

Vulnerability assessment is essential for understanding and launching effective flood risk reduction strategies. This study aimed to examine the vulnerability of flood-prone rural communities in southern Punjab, Pakistan to external shocks. The concept of vulnerability encompasses a range of dimensions, including physical, social, institutional, environmental, economic, and attitudinal. Using a composite index method, indices were developed for each dimension and combined to create a multidimensional measure of vulnerability. A sample of 365 communities was selected using the Yamane sampling technique, and data were collected through a questionnaire containing 65 indicators across all dimensions. Descriptive statistics and ANOVA tests were used to analyze the data. The results show that communities near the Chenab River had higher attitudinal and institutional vulnerability compared to other communities. High attitudinal vulnerabilities were associated with poorly perceived flood risks and low preparedness measures, whereas institutional vulnerabilities were driven by conventional flood protection strategies, lack of institutional trust, and lack of flood risk awareness. This research provides insights into the various components of vulnerability in flood-prone rural communities in Pakistan and demonstrates a useful methodology that can be applied to other disasters at different spatial scales.

Urbanization affects plant species diversity of stormwater ponds in a large German city

Urban stormwater ponds (SPs) are important for flood protection strategies in areas with heavily sealed soils as they mitigate the negative effects of floods. SPs with temporary waters (TWs) are only flooded when water levels or surface runoffs are high, while SPs with permanent waters (PWs) contain a permanently flooded area. In urban areas, SPs are important secondary habitats for plants and animals as natural aquatic and semi-aquatic habitats are often destroyed during urbanization. In 2017, a large survey on vascular plant diversity of 80 SPs was conducted in the city of Hamburg (Germany). The aim of the study was to analyze plant diversity of TWs and PWs and to identify relationships between plant diversity and different urbanization parameters. In total, 30% of the plant species pool of Hamburg was found in the surveyed SPs representing 0.03% of the total area of Hamburg. We found significant differences in the number and proportion of aquatic, threatened and non-native species between the shoreline and bottom of TWs and PWs. The number and proportion of aquatic species was positively correlated with the proportion of urban green and negatively correlated with the degree of soil sealing in the direct surrounding of SPs. For the proportion of threatened species in the bottom of TWs, a positive relationship was found with the proportion of urban green in the surrounding of SPs. For the number and proportion of non-native species in the shoreline of SPs, negative relationships were found with the proportion of urban green and the number of different habitat types in the surrounding of SPs. Further, a positive relationship with the degree of soil sealing was identified. Our results highlight the nature conservation value of urban SPs for plants and showed the negative effects of urbanization on several plant species groups.

Relationship between residential house damage and flood characteristics: A case study in the Teesta River Basin, Bangladesh

The flood damage function model is indispensable for flood damage assessment as it can provide useful information for establishing flood protection strategies. For the assessment of residential house damage in different areas, flood damage function models have been traditionally proposed considering only the depth–damage curve. However, flood duration and flood may also have an influence on flood damage. Conventionally, the damage rate was estimated based on information about monetary losses collected from local people or insurance payout databases. This research proposes a new methodology to establish a flood damage function model that considers flood depth, flood duration, and flood velocity. Field surveys were conducted in the Teesta River Basin of rural Bangladesh. For each house, a questionnaire survey was conducted to identify the flood information (flood depth, flood duration, and the qualitative representation of flood velocity), household structure information (area, plinth height, and ceiling height), structural damage mechanism, and the required amount of material and labor to repair the damage after each flood event. Finally, a flood damage function model including the impacts of house types and different flood parameters was established through multiple regression analysis. The consistency of the model was verified through the estimation of different statistical parameters. It can serve as a flood loss estimation model as it correlates flooding with various parameters, such as building materials and their damage mechanism.

Regional flood resilience grading based on GEM-AHPSort II method: An objective and managerial factors integrated perspective

Flood resilience is the principal capability of the flood-affected areas to quickly eliminate the impact of floods. Motivated by the realistic demand of improving the regional flood resilience and reducing negative hazards caused by flood, regional flood resilience evaluation is carried out from the perspective of objective and managerial factors in this paper. Firstly, a novel Multi Criteria Decision Making (MCDM) method G1-EW-MGLA (GEM)-AHPSort II method is proposed by combining AHPSort II method, G1-EW method, and MGLA method. Secondly, the evaluation indicator system of regional flood resilience is constructed from the perspective of objective and managerial factors. Subsequently, the proposed method and indicator system were applied to the case of flood resilience evaluation in Hubei Province, China. The case study analysis results show that in the 17 regions involved in the evaluation, the number of regions with “medium-low resilience” and “low resilience” is close to half, and the flood resilience of the regions with high economic development tends to be a higher level. In addition, under the same case data, the evaluation results of the proposed GEM-AHPSort II method are compared against the EW-AHPSort II method and AHPSort II method. The indicator weights determination process of GEM-AHPSort II method has been improved compared with the other two methods, and the evaluation results are more practical. Finally, some management suggestions for effectively improving the regional flood resilience and reducing flood hazards were put forward. This paper can provide a reference for the government to formulate or improve relevant flood protection strategies.

Taming the torrent: changes in flood protection at the Gürbe River (Switzerland) from the nineteenth century until today

This paper analyses the flood protection history of the Gürbe River (Switzerland), a 29-km-long tributary of the Aare River. The upper reach of the river has the character of a mountain torrent and an exceptionally difficult flooding situation. For centuries, riparian communities were only able to take small protective measures. In the mid-nineteenth century, the flood protection strategy changed: between 1855 and 1881, the Gürbe River was channelised and stabilised by a torrent control system. Although the situation improved, flood damage could not be prevented as intended. Therefore, dozens of consecutive projects were implemented—without interruption until today. This paper examines why small watercourses are useful case studies, which protection measures were taken at the Gürbe River, how they corresponded to the prevailing flood protection philosophy, whether they were linked to floods and how flood protection influenced land use. The Gürbe regulation, its consecutive projects and the connected drainages had far-reaching effects: They allowed an intensive agricultural use of the valley floor, the construction of roads, a railway, and new settlements. Consequently, the social and economic pressure on the hazard area increased steadily over the decades. It created a vicious circle: the more that protective structures were built, the more important and profitable flood prevention became, and the more structures were raised. A reevaluation finally took place in the late twentieth century, based on increasing environmental awareness, and fostered by a catastrophic flood. However, the implementation of new projects proved to be difficult due to conflicting interests.

House Prices and Flood Risk Exposure: An Integration of Hedonic Property Model and Spatial Econometric Analysis

The impact of climate change is devastating in developing countries where flood protection and insurance schemes are limited. Certain parts of Ho Chi Minh City, Vietnam are under the constant threat of inundation due to sea-level rise. We integrate the hedonic property model in a difference-in-differences framework and spatial econometric analysis into a single analytical framework to estimate the economic effect of pluvial flooding. We find prices for affected houses were discounted by 9% after a large flood event on 30 September 2017. This research contributes to the existing literature as follows. First, we study the economic impact of pluvial floods, which has received less attention in existing studies where large and irregular floods are their focus. Second, the inclusion of legal status as a control variable accounts for the unique character of the Vietnamese housing market. Third, we also identify the recovery of house prices after the flood event.

Flood risk management in New Zealand: A case study of the Northland urban community

The Northland river is characterised by having a short stream and large catchments. Heavy rains in the region trigger the rapid rise of the water levels and causes flooding, affecting the urban community in the flood plain with flash floods and river overflow as double threats. The government-initiated programs to protect urban communities such as ‘predict and mitigate’ but primarily focuses on physical infrastructure protection. While providing infrastructure is beneficial, developing a resilient community comprises more holistic strategies. There is a need for improving the local capacity to enhance resilience. A resilient, human-focused mitigation strategy which includes the affected communities, as well as the existing infrastructure, can reduce flood risks more efficiently. This paper explores the ways the Northland communities follow to mitigate existing flood risks, including their perceptions of the current flood protection strategies. This study investigates also the social and cultural elements that influence responses to flood risks. The main recommendation, of the study advocates a community-based risk management plan to complement the government’s strategy to efficiently mitigate flood risk in the urban Northland.

Net-zero carbon dioxide emissions in flood defence schemes

This paper compares the carbon dioxide emissions of constructing flood protection schemes with the emissions saved by providing flood defences. There is considerable information available on the carbon dioxide ‘cost’ of construction, but less on repairing flooded properties. Drawing on existing research into flooding, this paper identifies a carbon dioxide cost of repairs of 6 tonnes carbon dioxide equivalent per property flooded and uses this to provide a method to determine emission benefit for constructing flood protection schemes. While emission reduction should be the first priority, flood defences defend against future emissions. Using Stonehaven in the UK as a case study, this paper demonstrates that the carbon dioxide cost of constructing a flood protection scheme can be less than the carbon dioxide cost of undertaking repairs following flooding over the life of a scheme, with a benefit ratio of 2 identified for the case study scheme. The paper concludes with a review of the UK government appraisal process and cautions that the carbon value many not differentiate a flood protection scheme option when compared with capital cost. It is considered that an independent assessment should be undertaken to demonstrate that a net-zero-emission option is selected.

Longue Durée

New approaches to combine flood protection, soil regeneration and water management strategies with urban design, landscape architecture and spatial planning in delta regions cannot do without knowledge and understanding of history. To find a new balance between urbanization, climate change, geopolitical shifts, the energy transition in deltas it is crucial to understand the evaluation of the system from the past to what it is today and can be in the future. The logic of the relationship between design, engineering, science and governance on the one hand, and the logic with the natural system on the other, determined the current conditions and its performance. In the development of cities, at any time, there is the concept of Longue Durée recognizing the formative forces of nature and the relevance of historic concepts to take into account (Braudel, 1949). The main question of this issue is: How can interdisciplinary approaches of design, engineering, science and governance respond to the environmental crisis and steer upon the Longue Durée of the delta?

Participatory value evaluation for the evaluation of flood protection schemes

Participatory Value Evaluation (PVE) is a new survey method which elicits citizens' preferences over the allocation of public budgets as well as their private income. In a PVE, citizens are asked to choose the best portfolio of projects given a governmental and a private budget constraint. First, this paper aligns PVE with the traditional Kaldor-Hicks welfare economics framework underlying many Cost-Benefit Analyses. Second, this paper positions PVE against other valuation methods. Third, this paper applies the PVE method to evaluate the impacts of projects mitigating flood risks in the Netherlands. This empirical application reveals that Dutch citizens indicate a preference for projects that combine strengthening dikes and give space to the river to flood safely, particularly when such projects positively influence biodiversity and recreational opportunities.

Can urban parks help with disaster risk reduction through educational awareness? A case study of Hurricane Harvey

This study examines the relationship between educational awareness and natural disasters through the lens of flood mitigation and also attempts to understand the perceptional and socio-demographical impacts in flood-prone areas. Recorded as one of the most catastrophic storms in the U.S., Hurricane Harvey caused massive damages to the environment and negatively affected public health and well-being. Having sustained three flood events since opening, including Hurricane Harvey, Buffalo Bayou Park in Houston, Texas, became the case study for this research as its role relative to educational awareness and natural disasters became the focus. The study performed a questionnaire-based survey with park users. Findings showed that concerns existed with respect to park use, socio-demographics, and accessibility. The findings also showed, however, that the park design contributed to flood mitigation strategies through establishment of educational awareness of natural disasters. This awareness was confirmed by park users being knowledgeable of some flood protection strategies, including planting native and local plants and curving the bayous naturally. Also, park users noted their preference for receiving disaster-related educational news via social media and partnerships/non-profit organizations. Finally, none of the socio-demographic features showed a difference for the logistic regression model as a significant predictor while attending educational events and residing within 20 min of the park significantly increased flood-mitigation awareness. This study highlights several efficient strategies that can complement the role of urban parks relative to how people experience and perceive educational activities concerning natural disasters.

Ecological consequences of sea level rise and flood protection strategies in shallow coastal systems: A quick-scan barcoding approach

Shallow coastal ecosystems have high ecological value and contribute to flood protection. Their stability is, however, sensitive to the amount and rate of future sea level rise (SLR), their ability to trap sediment which allows them to grow with rising sea level, and human response to SLR. So far, studies have focused on assessing SLR impacts using resource-intensive tools. Here, we present an approach for a first-order assessment and easily accessible ‘barcode’ visualization to rapidly assess potential impacts of both SLR and adaptation strategies on coastal ecosystems in a spatially explicit way. Our approach relates habitat types (ecotopes) to water level, morphology and salinity, allowing users to determine shifts in spatial arrangements of ecological zones under different SLR rates and strategies. We illustrate this approach for a transect in the Dutch Wadden Sea. We find that beyond a critical rate of SLR, major changes in ecotope distribution are projected to occur as this part of the Wadden Sea starts to drown due to insufficient sediment import. Even larger impacts arise from adaptation strategies. Closing the barrier islands will turn the Wadden Sea into a freshwater lake-system with the absence of intertidal areas, infilling of channels and bank erosion. A strategy that allows for inland migration of the shoreline, results in a deep tidal basin with large subtidal habitats, and a shifted intertidal zone. Our case study shows that the barcoding approach provides a rapid, quantitative and spatially explicit overview of the potential implications for coastal ecosystems under different SLR scenarios, adaptation strategies and time horizons. This can then be used to screen adaptation strategies before going into a more comprehensive analysis. The barcode visualization allows for easy dissemination of potential ecological impacts to a broad community.

Regional economic analysis of flood defence heights at the German Baltic Sea coast: A multi-method cost-benefit approach for flood prevention

Mean and extreme sea-level uncertainties, as well as uncertainty about future flood exposure, hinder the risk-based optimisation of flood protection investments. To deal with these uncertainties, cost-benefit analysis (CBA) and methods for robust decision-making can be combined. This paper sequentially applies CBA, robust optimisation methods and info-gap analysis to find efficient and robust coastal flood protection strategies for the German Baltic Sea coast. The CBA results suggest that – under flood risk assumptions – a share of the coast of Schleswig-Holstein (9.3–10.1%; 60–65 km) and Mecklenburg-Vorpommern (4.1–10.0%; 78–189 km) with relatively high flood exposure, might currently be under-protected from a social welfare perspective. Present Value estimates of regional investment costs of five regret or loss minimising strategies range from 1.7 to 4.8 billion Euro across robustness metrics at 3% discounting. The info-gap analysis suggests that some of these strategies will fail to prevent large-scale damages under high-end scenarios. We conclude that a multi-method cost-benefit approach can be used to narrow down the number of solutions that are both potentially efficient and sufficiently robust by investigating strategy performance within, across and beyond predefined scenarios.

Innovative Techniques in the Context of Actions for Flood Risk Management: A Review

The general purpose of this review paper is to provide an overview of various flood protection strategies because flooding is becoming more frequent and is affecting more areas, displacing people, and increasing fatalities around the world. The concern surrounding climate change resulting in sea level rise, increasingly frequent storm events, and the need for adaptive actions to better control urban storm water runoff motivates the completion of this paper. Understanding the impact of climate change aside from dangerous weather conditions essential for designing effective mitigation strategies, but first, there needs to be a clear and strong understanding of the effects of extreme events. This review represents engineered storm water practices that are adaptive, in combination with the non-structural measures such as urban planning, will help reduce flood impact.

Are we expecting too much from the private sector in flood adaptation? Scenario-based field experiments with small- and medium-sized firms in Ho Chi Minh City, Vietnam

Adaptive governance approaches emphasize the crucial role of the private sector in enabling climate change adaptation. Yet, the participation of local firms is still lacking, and little is known about the conditions potentially influencing firms’ adaptation decisions and mechanisms that might encourage private sector engagement. We address this gap with an empirical analysis of the willingness of manufacturing small- and medium-sized enterprises (SMEs) to participate financially in collective flood adaptation in Ho Chi Minh City (HCMC), a hotspot of future climate change risk. Using scenario-based field experiments, we shed light on internal and external conditions that influence potential investments in collective initiatives and explain what role SMEs can play in flood adaptation. We find that direct impacts of floods, perceived self-responsibility, and strong local ties motivate firms to participate in collective adaptation, whereas government support, sufficient financial resources, and previously implemented flood protection strategies reduce the necessity to act collectively. Here, opportunity costs and the handling of other business risks play a decisive role in investment decisions. This study shows that although private sector engagement appears to be a promising approach, it is not a panacea. Collective initiatives on flood adaptation need formal guidance and should involve local business networks and partnerships to give voice to the needs and capacities of SMEs, but such initiatives should not overstretch firms’ responsibilities.

Cooperation in flood risk management: understanding the role of strategic planning in two Austrian policy instruments

Strategic land use planning assumes a pivotal role in flood risk management. By using formal instruments, spatial planning can (i) legally secure areas for flood retention or other flood protection measures (hazard reduction) as well as (ii) regulate settlement development in hazard areas and ensure flood-adapted land uses (damage prevention). The interrelations between upstream and downstream riparian areas in flood risk management, however, require regional or catchment-oriented approaches in strategic land use planning to better coordinate land development options along rivers. This paper examines two strategic planning instruments in Austrian flood risk management. The two instruments – Blauzone Rheintal in Vorarlberg and Schutzwasserwirtschaftlicher Raumentwicklungsplan (SREP) in Carinthia – were developed by water authorities and spatial planning departments to prevent settlement growth in flood-prone areas and to secure land for flood protection schemes. Despite having similar problems in their backgrounds and objectives, the implementation processes of these instruments differ significantly: while the Blauzone Rheintal was formalized as a legally binding regional land use plan, the SREP was not developed beyond the pilot stage. This paper identifies important contextual conditions and lessons learned to facilitate the scaling-up and replication of catchment-oriented spatial planning instruments in other flood-prone regions.

Inference for Extreme Values Under Threshold-Based Stopping Rules

SummaryThere is a propensity for an extreme value analysis to be conducted as a consequence of a large flooding event. This timing of the analysis introduces bias and poor coverage probabilities into the associated risk assessments and leads subsequently to inefficient flood protection schemes. We explore these problems through studying stochastic stopping criteria and propose new likelihood-based inferences that mitigate against these difficulties. Our methods are illustrated through the analysis of the river Lune, following its experiencing the UK's largest ever measured flow event in 2015. We show that without accounting for this stopping feature there would be substantial overdesign in response to the event.

Long-term Changes of Waves at the German Baltic Sea Coast: Are There Trends from the Past?

Dreier, N.; Mannikus, R., and Frohle, P., 2020. Long-term changes of waves at the German Baltic Sea Coast: Are there trends from the past? In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020.JournalofCoastalResearch,SpecialIssueNo.95,pp.1416–1421.CoconutCreek(Florida),ISSN0749-0208.For the development of future coastal and flood protection strategies and methods as well as the adaptation of today's existing protection structures, possible impacts of climate change on the long-term changes of the local wave conditions in the future and the past need to be analysed and assessed. In this study, two main research questions are raised: (i) Are there any long-term changes of the waves derived from numerical model data?, (ii) How well can the COSMO model reproduce the wave climate for the past? To answer those questions, two reanalysis wind data sets (COSMO-REA6 and coastDat2) for the past based on the COSMO model are used for the calculation of long-term time series of hourly wave parameters (SWAN) at the German Baltic Sea Coast. The long-term changes of the average wave conditions in the past are analysed and assessed for the coastDat2 data set for both average values and the frequency of occurrence of significant wave height and mean wave direction over time periods of 30 years. Moreover, the statistical significance of the changes of the frequency is assessed based on statistical hypothesis tests. In agreement with previous analysis of the future long-term changes of the wave climate, a large multi-(decadal), spatial and seasonal variability of the changes exist and the changes depend on the exposition of the coast towards the prevailing westerly winds. At westerly wind exposed locations, trends towards an increase of the 30 year annual averages of significant wave height up to 5 % were found, with possible larger changes of the 30 year seasonal averages, and trends towards more waves coming from westerly directions. The long-term changes of extreme wave conditions in the past are analysed based on extreme value statistics and over time periods of 30 years. Slightly increasing respectively decreasing trends between -5 % and +9 % (-0.16 m/+0.27 m) of significant wave heights with a return period of 200 years have been found at westerly respectively easterly wind exposed locations.

A Flood Damage Allowance Framework for Coastal Protection With Deep Uncertainty in Sea Level Rise.

Deep uncertainty describes situations when there is either ignorance or disagreement over (1) models used to describe key system processes and (2) probability distributions used to characterize the uncertainty of key variables and parameters. Future projections of Antarctic ice sheet (AIS) mass loss remain characterized by deep uncertainty. This complicates decisions on long‐lived coastal protection projects when determining what margin of safety to implement. If the chosen margin of safety does not properly account for uncertainties in sea level rise, the effectiveness of flood protection could decrease over time, potentially putting lives and properties at a greater risk. To address this issue, we develop a flood damage allowance framework for calculating the height of a flood protection strategy needed to ensure that a given level of financial risk is maintained. The damage allowance framework considers decision maker preferences such as planning horizons, protection strategies, and subjective views of AIS stability. We use Manhattan—with the population and built environment fixed in time—to illustrate how our framework could be used to calculate a range of damage allowances based on multiple plausible scenarios of AIS melt. Under high greenhouse gas emissions, we find that results are sensitive to the selection of the upper limit of AIS contributions to sea level rise. Design metrics that specify financial risk targets, such as expected flood damage, allow for the calculation of avoided flood damages (i.e., benefits) that can be combined with estimates of construction cost and then integrated into existing financial decision‐making approaches (e.g., benefit‐cost analysis).