Flood Risk Mitigation Strategies Research Articles

Determinants of flood risk mitigation strategies at household level: a case of Khyber Pakhtunkhwa (KP) province, Pakistan

Pakistan is one of the most adversely affected countries by climate-related extreme events such as floods owing to its geographical and climatic conditions. Over the last two decades, frequency and severity of flood events have been increased and has adversely affected the livelihood and well-being of millions of people in Pakistan. The development of effective mitigation policies requires a clear understanding of the impacts and local responses to extreme events, which is quite limited in Pakistan. This study used a dataset of 600 households collected through face-to-face interviews from two districts of Khyber Pakhtunkhwa province that were severely affected from 2010 floods. The correlation and probit model methods are used to assess the study objectives. The findings of the study revealed that elevated ground floor, foundation strengthening, construction of house with reinforced material and precautionary savings were the main adaptation measures adopted at household level. The results from the probit model showed that gender, age, location, monthly income, family size, house ownership, disability, and education influence the households’ choices of mitigation strategies. The study further indicated that adoption of mitigation strategies at household level is constrained by several factors, i.e., financial constraint, lack of early warning system, lack of land use planning and inadequate resources. Further mitigation strategies also varied across different groups of households based on education, age, and income. Additionally the study discovered that the local policies on disaster management need to be improved to address the barriers to the adoption of advanced level adaptation measures at the household level such as advanced level early warning system, flood forecasting and dissemination of updated information and support, house building codes, infrastructure building practices, and adequate spatial planning.

Probabilistic flood inundation mapping at ungauged streams due to roughness coefficient uncertainty in hydraulic modelling

Abstract. Probabilistic flood inundation mapping is performed and analysed at the ungauged Xerias stream reach, Volos, Greece. The study evaluates the uncertainty introduced by the roughness coefficient values on hydraulic models in flood inundation modelling and mapping. The well-established one-dimensional (1-D) hydraulic model, HEC-RAS is selected and linked to Monte-Carlo simulations of hydraulic roughness. Terrestrial Laser Scanner data have been used to produce a high quality DEM for input data uncertainty minimisation and to improve determination accuracy on stream channel topography required by the hydraulic model. Initial Manning's n roughness coefficient values are based on pebble count field surveys and empirical formulas. Various theoretical probability distributions are fitted and evaluated on their accuracy to represent the estimated roughness values. Finally, Latin Hypercube Sampling has been used for generation of different sets of Manning roughness values and flood inundation probability maps have been created with the use of Monte Carlo simulations. Historical flood extent data, from an extreme historical flash flood event, are used for validation of the method. The calibration process is based on a binary wet-dry reasoning with the use of Median Absolute Percentage Error evaluation metric. The results show that the proposed procedure supports probabilistic flood hazard mapping at ungauged rivers and provides water resources managers with valuable information for planning and implementing flood risk mitigation strategies.

Probabilistic life-cycle cost-benefit analysis of portfolios of buildings under flood hazard

Nowadays, the number of residential buildings in flood prone zones is increasing significantly. Therefore, for these buildings, it is of vital importance to apply hazard risk mitigation strategies. In this paper, probabilistic cost-benefit analysis of flood risk mitigation strategies for portfolios of residential buildings is performed in a life-cycle context. Additionally, an efficient methodology is proposed to aid decision-makers on whether or not to retrofit portfolios of structures considering both expected and standard deviation of life-cycle cost. The vulnerability model of buildings under flood hazard is introduced considering serviceability and ultimate limit states. Probabilistic cost-benefit analysis is performed by comparing the effectiveness of different retrofit actions. Additionally, uncertainty and correlation effects are considered in the probabilistic loss and cost-benefit analysis procedures. The proposed approach is applied to a portfolio of residential buildings located in Florida to illustrate its capability and application. However, the proposed approach is general and can be applied to buildings located in other regions.

A study of flood risk mitigation strategies in vernacular dwellings of Rathnapura, Sri Lanka

This study examines the flood mitigation strategies in vernacular dwellings in the high flood risk district of Rathnupra, Sri Lanka. In order to mitigate flood risks, local communities have devised successful flood risk mitigation strategies especially in relation to construction of dwellings. However the adaptive capacity of the local people is not well understood as limited research has been conducted on their ability to mitigate flood risk. This study consists of 15 case studies in three flood risk zonal categories of Rathnapura. The time period of construction of these dwellings span from 1800 to 2005, allowing the authors to conduct a chronological analysis of development of materials and construction practices in mitigating flood risk in Rathnapura. The study takes the new guidelines for flood risk mitigation in Rathnapura as a framework to analyze the vernacular knowledge demonstrated in the case studies. The planning, spatial configuration, and construction methods were documented for the 15 case studies. The study concludes that the single-storey dwelling constructed in the 1800 and early 1900 demonstrate many of the flood mitigation features required by modern guidelines. The study also emphasizes the lack of attention to services such as plumbing and electricity in the case studies as well as in the modern guidelines.

Simplified graphical tools for assessing flood-risk change over large flood-prone areas

Abstract. We propose and investigate the reliability of simplified graphical tools, which we term Hypsometric Vulnerability Curves, HVCs, for assessing flood vulnerability and risk over large geographical areas and for defining sustainable flood-risk mitigation strategies. These curves rely on the use of inundation scenarios simulated by means of quasi-two-dimensional (quasi-2-D) hydrodynamic models that reproduce the hydraulic behaviour of the floodable area outside the main embankment system of the study river reach. We present an application of HVCs constructed on the basis of land use and census data collected during the last 50 years for assessing the recent dynamics of the flood vulnerability and risk over a large floodable area along a 350 km stretch of the River Po (Northern Italy). We also compared the proposed simplified approach with a traditional approach based on simulations performed with the fully-2-D hydrodynamic model TELEMAC-2-D, a widely employed and well-known 2-D finite-element scheme. By means of this comparison, we characterize the accuracy of the proposed simplified approach (i.e. quasi-2-D model and HVCs) for flood-risk assessment over large geographical areas and different historical land-use scenarios.

Probabilistic flood hazard mapping: effects of uncertain boundary conditions

Abstract. Comprehensive flood risk assessment studies should quantify the global uncertainty in flood hazard estimation, for instance by mapping inundation extents together with their confidence intervals. This appears of particular importance in the case of flood hazard assessments along dike-protected reaches, where the possibility of occurrence of dike failures may considerably enhance the uncertainty. We present a methodology to derive probabilistic flood maps in dike-protected flood prone areas, where several sources of uncertainty are taken into account. In particular, this paper focuses on a 50 km reach of River Po (Italy) and three major sources of uncertainty in hydraulic modelling and flood mapping: uncertainties in the (i) upstream and (ii) downstream boundary conditions, and (iii) uncertainties in dike failures. Uncertainties in the definition of upstream boundary conditions (i.e. design-hydrographs) are assessed through a copula-based bivariate analysis of flood peaks and volumes. Uncertainties in the definition of downstream boundary conditions are characterised by uncertainty in the rating curve with confidence intervals which reflect discharge measurement and interpolation errors. The effects of uncertainties in boundary conditions and randomness of dike failures are assessed by means of the Inundation Hazard Assessment Model (IHAM), a recently proposed hybrid probabilistic-deterministic model that considers three different dike failure mechanisms: overtopping, piping and micro-instability due to seepage. The results of the study show that the IHAM-based analysis enables probabilistic flood hazard mapping and provides decision-makers with a fundamental piece of information for devising and implementing flood risk mitigation strategies in the presence of various sources of uncertainty.

Towards dynamics in flood risk assessment

Abstract. As a consequence of flood impacts, communities inhabiting mountain areas are increasingly affected by considerable damage to infrastructure and property. The design of effective flood risk mitigation strategies and their subsequent implementation is crucial for a sustainable development in mountain areas. The assessment of the dynamic evolution of flood risk is the pillar of any subsequent planning process that is targeted at a reduction of the expected adverse consequences of the hazard impact. Given these premises, firstly, a comprehensive method to derive flood hazard process scenarios for well-defined areas at risk is presented. Secondly, conceptualisations of a static and dynamic flood risk assessment are provided. These are based on formal schemes to compute the risk mitigation performance of devised mitigation strategies within the framework of economic cost-benefit analysis. In this context, techniques suitable to quantify the expected losses induced by the identified flood impacts are provided.

Physical Vulnerability Assessment Based on Fluid and Classical Mechanics to Support Cost-Benefit Analysis of Flood Risk Mitigation Strategies

The impacts of flood events that occurred in autumn 2011 in the Italian regions of Liguria and Tuscany revived the engagement of the public decision-maker to enhance the synergy of flood control and land use planning. In this context, the design of efficient flood risk mitigation strategies and their subsequent implementation critically relies on a careful vulnerability analysis of the fixed and mobile elements exposed to flood hazard. In this paper we develop computation schemes enabling dynamic vulnerability and risk analyses for a broad typological variety of elements at risk. To show their applicability, a series of prime examples are discussed in detail, e.g. a bridge deck impacted by the flood and a car, first displaced and subsequently exposed to collision with fixed objects. We hold the view that it is essential that the derivation of the computational schemes to assess the vulnerability of endangered objects should be based on classical and fluid mechanics. In such a way, we aim to complement from a methodological perspective the existing, mainly empirical, vulnerability and risk assessment approaches and to support the design of effective flood risk mitigation strategies by defusing the main criticalities within the systems prone to flood risk.

Identifying robust large-scale flood risk mitigation strategies: A quasi-2D hydraulic model as a tool for the Po river

This paper focuses on the identification of large-scale flood risk mitigation strategies for the middle-lower reach of River Po, the longest Italian river and the largest in terms of streamflow. This study develops and tests the applicability of a quasi-2D hydraulic model to aid the identification of large-scale flood risk mitigation strategies relative to a 500-year flood event other than levee heightening, which is not technically viable nor economically conceivable for the case study. Different geometrical configurations of the embankment system are considered and modelled in the study: no overtopping; overtopping and levee breaching; overtopping without levee breaching. The quasi-2D model resulted in being a very useful tool for (1) addressing the problem of flood risk mitigation from a global - perspective (i.e., entire middle-lower reach of River Po), (2) identifying critical reaches, inundation areas and corresponding overflow volumes, and (3) generating reliable boundary conditions for smaller scale studies aimed at further analyzing the hypothesized flood mitigation strategies using more complex modelling tools (e.g., fully 2D approaches). These are crucial tasks for institutions and public bodies in charge of formulating robust flood risk management strategies for large European rivers, in the light of the recent Directive 2007/60/EC on the assessment and management of flood risks ( European Parliament, 2007).

Strategies for Mitigation of Flood Risk in the Niger Delta, Nigeria

The study has the major objective of evaluating flood risk mitigation strategies in the Niger Delta, a coastal region of Nigeria that suffers from perennial flooding. The Raper argues that the structural methods of flood control tends to give a false sense of security to flood plain dwellers and thereby encouraging investments in flood prone areas. The non-structural methods on the other hand are basically behavioural adjustments to flood control. The study observes that for flood risk mitigation strategies to be effective in the Niger Delta, there is need for establishment of coastal management zone authority, land-use zoning, legislation, building codes, flood forecasting and warning systems, flood insurance and engineering control of the major river systems