Michael J. Hammond

Urban flood impact assessment: A state-of-the-art review

Flooding can cause major disruptions in cities, and lead to significant impacts on people, the economy and on the environment. These impacts may be exacerbated by climate and socio-economic changes. Resilience thinking has become an important way for city planners and decision makers to manage flood risks. Despite different definitions of resilience, a consistent theme is that flood resilient cities are impacted less by extreme flood events. Therefore, flood risk professionals and planners need to understand flood impacts to build flood resilient cities. This paper presents a state-of-the-art literature review on flood impact assessment in urban areas, detailing their application, and their limitations. It describes both techniques for dealing with individual categories of impacts, as well as methodologies for integrating them. The paper will also identify future avenues for progress in improving the techniques.

Water allocation assessment in low flow river under data scarce conditions: A study of hydrological simulation in Mediterranean basin

River Francolí is a small river in Catalonia (northeastern Spain) with an average annual low flow (~2 m(3)/s). The purpose of the River Francolí watershed assessments is to support and inform region-wide planning efforts from the perspective of water protection, climate change and water allocation. In this study, a hydrological model of the Francolí River watershed was developed for use as a tool for watershed planning, water resource assessment, and ultimately, water allocation purposes using hydrological data from 2002 to 2006 inclusive. The modeling package selected for this application is DHIs MIKE BASIN. This model is a strategic scale water resource management simulation model, which includes modeling of both land surface and subsurface hydrological processes. Topographic, land use, hydrological, rainfall, and meteorological data were used to develop the model segmentation and input. Due to the unavailability of required catchment runoff data, the NAM rainfall-runoff model was used to calculate runoff of all the sub-watersheds. The results reveal a potential pressure on the availability of groundwater and surface water in the lower part of River Francolí as was expected by the IPCC for Mediterranean river basins. The study also revealed that due to the complex hydrological regime existing in the study area and data scarcity, a comprehensive physically based method was required to better represent the interaction between groundwater and surface water. The combined ArcGIS/MIKE BASIN models appear as a useful tool to assess the hydrological cycle and to better understand water allocation to different sectors in the Francolí River watershed.

From hazard to impact: flood damage assessment tools for mega cities

In this paper, a set of GIS-based tools is presented that combines information from hydraulic modelling results, spatially varied object attributes and damage functions to assess flood damage. They can directly process the outputs of hydraulic modelling packages to calculate the direct tangible damage, the risk to life, and the health impact of individual flood events. The tools also combine information from multiple events to calculate the expected annual damage. The land cover classes from urban growth models can be also used in the tools to assess flood damage under future conditions. This paper describes the algorithms implemented, and the results of their application in the mega city of Dhaka in Bangladesh. Complications and technical issues in real-world applications are discussed, and their solutions are also presented. Although it is difficult to obtain reliable data for model validation, the sensitivity of the results to spatial resolution and input parameters is investigated to demonstrate that the tools can provide robust estimations even with coarse data resolution, when a fine masking cell size is used. The tools were designed to be flexible, so that they can also be used to evaluate different hazard impacts, and adopted in various GIS platforms easily.

System-focused risk identification and assessment for disaster preparedness: Dynamic threat analysis

Current approaches to risk management stress the need for dynamic (i.e. continuous, ongoing) approaches to risk identification as part of a planned resource application aimed at reducing the expected consequences of undesired outcomes for the object of the assessment. We contend that these approaches place insufficient emphasis on the system knowledge available to the assessor, particularly in respect of three factors, namely the dynamic behavior of the system under threat, the role of human agents and the knowledge availability to those agents.

A new methodology for modelling of health risk from urban flooding exemplified by cholera – case Dhaka, Bangladesh

The phenomenon of urban flooding due to rainfall exceeding the design capacity of drainage systems is a global problem and can have significant economic and social consequences. This is even more extreme in developing countries, where poor sanitation still causes a high infectious disease burden and mortality, especially during floods. At present, there are no software tools capable of combining hydrodynamic modelling and health risk analyses, and the links between urban flooding and the health risk for the population due to direct contact with the flood water are poorly understood. The present paper outlines a novel methodology for linking dynamic urban flood modelling with quantitative microbial risk assessment (QMRA). This provides a unique possibility for understanding the interaction between urban flooding and health risk caused by direct human contact with the flood water and hence gives an option for reducing the burden of disease in the population by use of intelligent urban flood risk management. The model linking urban flooding and health risk is applied to Dhaka City in Bangladesh, where waterborne diseases including cholera are endemic. The application to Dhaka City is supported by measurements of pathogens in the urban drainage system. The outcome of the application indicates that direct contact with polluted flood water is a plausible route of primary transmission of cholera and demonstrates the applicability and the potential for linking urban flood models with QMRA in order to identify interventions to reduce the burden of disease on the population in Dhaka City.

Flood Impacts on Road Transportation Using Microscopic Traffic Modelling Techniques

This paper proposes a novel methodology for modelling the impacts of floods on traffic. Often, flooding is a complex combination of various causes (coastal, fluvial and pluvial). Further, transportation systems are very sensitive to external disturbances. The interactions between these two complex and dynamic systems have not been studied in detail so far. To address this issue, this paper proposes a methodology for a dynamic integration of a flood model (MIKE FLOOD) and a microscopic traffic simulation model (SUMO). The flood modelling results indicate which roads are inundated for a period of time. The traffic on these links will be halted or delayed according to the flood characteristics—extent, propagation and depth. As a consequence, some of the trips need to be cancelled; some need to be rerouted to unfavourable routes; and some are indirectly affected. A comparison between the baseline and a flood scenario yields the impacts of that flood on traffic, estimated in terms of lost business hours, additional fuel consumption and additional CO2 emissions. The proposed methodology will be further developed as a workable tool to evaluate the flooding impact on transportation network at city scale automatically.

Back to the future: assessing the damage of 2004 Dhaka flood in the 2050 urban environment

Planning to make a city flood resilient needs proper assessment of future conditions. Urban growth models are being used as a planning tool for city development. Within the project Collaborative Research in Flood Resilience in Urban Areas (CORFU), flood management strategies suitable for cities with varied geographic and socio-economic conditions have been developed. In the paper, we adopted urban growth model to project the possible future conditions of Dhaka City, the rapidly developing capital of Bangladesh. Bangladesh lies in the delta of the Himalayan Mountain range and experiences frequent flooding. In 2004 an extreme nationwide flood event occurred, which caused major damage to Dhaka City. If the same event were to occur in 2050, it can be expected that the damage would increase significantly. Through the application of the urban growth, hydraulic and damage assessment models, we were able to determine the damage that can be expected to happen in 2050. The paper also describes the key factors that are important to determine this impact and the associated uncertainties.

Human Agency in Disaster Planning: A Systems Approach: Human Agency in Disaster Planning

Current approaches to risk management place insufficient emphasis on the system knowledge available to the assessor, particularly in respect of the dynamic behavior of the system under threat, the role of human agents (HAs), and the knowledge available to those agents. In this article, we address the second of these issues. We are concerned with a class of systems containing HAs playing a variety of roles as significant system elements-as decisionmakers, cognitive agents, or implementers-that is, human activity systems. Within this family of HAS, we focus on safety and mission-critical systems, referring to this subclass as critical human activity systems (CHASs). Identification of the role and contribution of these human elements to a system is a nontrivial problem whether in an engineering context, or, as is the case here, in a wider social and public context. Frequently, they are treated as standing apart from the system in design or policy terms. Regardless of the process of policy definition followed, analysis of the risk and threats to such a CHAS requires a holistic approach, since the effect of undesirable, uninformed, or erroneous actions on the part of the human elements is both potentially significant to the system output and inextricably bound together with the nonhuman elements of the system. We present a procedure for identifying the potential threats and risks emerging from the roles and activity of those HAs, using the 2014 flooding in southwestern England and the Thames Valley as a contemporary example.

Back to the future: assessing the damage of 2004 Dhaka flood in the 2050 urban environment: Assessing the damage of 2004 Dhaka flood

Planning to make a city flood resilient needs proper assessment of future conditions. Urban growth models are being used as a planning tool for city development. Within the project Collaborative Research in Flood Resilience in Urban Areas (CORFU), flood management strategies suitable for cities with varied geographic and socio-economic conditions have been developed. In the paper, we adopted urban growth model to project the possible future conditions of Dhaka City, the rapidly developing capital of Bangladesh. Bangladesh lies in the delta of the Himalayan Mountain range and experiences frequent flooding. In 2004 an extreme nationwide flood event occurred, which caused major damage to Dhaka City. If the same event were to occur in 2050, it can be expected that the damage would increase significantly. Through the application of the urban growth, hydraulic and damage assessment models, we were able to determine the damage that can be expected to happen in 2050. The paper also describes the key factors that are important to determine this impact and the associated uncertainties.

Evaluation of Adaptation Strategies for Urban Flooding in Central Taipei City in Taiwan

The urban areas have been rapidly developed in Taiwan in recent years. The expanding urban areas and the increasing population, especially in the metropolitan Taipei city, result in surface runoff discharge during typhoons or rainstorms. When the surface runoff exceeds the capacity of drainage systems of the city, the urban inundation and property losses occur. The urban flooding risk assessment is a useful tool for the decision-making in flood damage mitigation. In general, hazard and vulnerability are two main factors for the risk assessment. In the present study, the Center Taipei City (CTC) is chosen as the study area. The A1B scenario simulations proposed by IPCC are used to compare the flood risks between the present situation and future condition which is under climate change scenario. The ArcGIS is used to yield the flood potential information and the flood risk for the return period of 10, 25, 100 and 200-year flood. The simulated results revealed that the increasing water storage to meet the regulation of the Taipei City government would effectively reduce the effects of climate change on the decreasing inundation areas. The adaptation strategies will also reduce the high-risk areas in the CTC according to risk assessment. The adaptation strategies composed of increasing the water storage in urban areas and reducing the social vulnerability of flooding area are the effective way for the flood risk reduction in urban area.