Albert S. Chen

Comparison of 1D/1D and 1D/2D Coupled (Sewer/Surface) Hydraulic Models for Urban Flood Simulation

Recent developments in flood modeling have led to the concept of coupled (sewer/surface) hydraulic models. In this paper two coupled models are examined; a one-dimensional (1D) sewer model coupled with a 1D surface network model (1D/1D) and a 1D sewer model coupled with a two-dimensional (2D) surface flow model (1D/2D). Flow over the terrain is better modeled by 2D models, whereas in confined channels 1D models provide a good approximation with less computational effort. This paper presents a comparison of the simulation results of 1D/1D model and a 1D/2D model. The methodology adopted for setting up the models is outlined and explained in detail as well as the 1D/1D modeling techniques used for reproducing the 1D/2D model results. The surface flow comparison clarifies the limitations of the 1D/1D model and indicates that the definition of the surface pathways, the linking elements sewer/surface, and inclusion of virtual manholes are key factors for setting up a more accurate 1D/1D model.

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.

An analysis of the combined consequences of pluvial and fluvial flooding

Intense rainfall in urban areas often generates both pluvial flooding due to the limited capacity of drainage systems, as well as fluvial flooding caused by deluges from river channels. The concurrence of pluvial and fluvial flooding can aggravate their (individual) potential damages. To analyse the impact caused by individual and composite type of flooding, the SIPSON/UIM model, an integrated 1D sewer and 2D overland flow was applied to numerical modelling. An event matrix of possible pluvial scenarios was combined with hypothetic overtopping and breaching situations to estimate the surface flooding consequences in the Stockbridge area, Keighley (Bradford, UK). The modelling results identified different flooding drivers in different parts of the study area and showed that the worst scenarios resulted from synthesised events.

Modelling sewer discharge via displacement of manhole covers during flood events using 1D/2D SIPSON/P-DWave dual drainage simulations

In urban areas, overloaded sewers may result in surcharge that causes surface flooding. The overflow from sewer systems mainly starts at the inlets until the pressure head in the manhole is high enough to lift up its cover, at which stage the surcharged flow may be discharged via the gap between the bottom of the manhole cover and the ground surface. In this paper, we propose a new approach to simulate such a dynamic between the sewer and the surface flow in coupled surface and sewer flow modelling. Two case studies are employed to demonstrate the differences between the new linking model and the traditional model that simplifies the process. The results show that the new approach is capable of describing the physical phenomena when manhole covers restrict the drainage flow from the surface to the sewer network and reduce the surcharge flow and vice versa.

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.

Complex of polyelectrolyte network with surfactant as novel shape memory networks.

Poly(acrylic acid-co-methyl methacrylate)-cetyltrimethylammonium bromide (P(AA-co-MMA)-C16TAB) complex has shape memory behavior due to the formation of crystalline aggregates among the long alkyl chains of C16TAB in the complex, and can be regarded as a novel shape memory network.

Rapid assessment of surface-water flood-management options in urban catchments

Abstract Surface-water flooding in urban areas has become a pressing issue due to changing precipitation patterns, expanding urban areas and ageing drainage infrastructure. Selection of flood-management options for widespread implementation using quantitative performance measures is both technically and computationally demanding, which limits the evidence available for decision support. This study presents a new framework for surface-water flood-intervention assessment at high resolution. The framework improves computational efficiency through utilisation of accessible data, simplified representations of interventions and a resource efficient cellular automata flood model. The advantages of this framework are demonstrated through an example case study where the performance of 12 high-level intervention strategies has been evaluated. Results from the case study demonstrate that the framework is able to provide quantitative performance values for a range of interventions. The speed of analysis supports the application of the framework as a decision-making tool for urban water planning.

Implications of rising flood-risk for employment location: a GMM spatial model with agglomeration and endogenous house price effects

The impact of flood-risk on local employment has been almost entirely neglected in the empirical urban economics literature. This omission is particularly anomalous in the context of climate change. We extend the literature in four ways. First, we argue that competition for land between firms and households will generate an endogenous role for house prices, which we estimate using a generalised method of moments two-stage least squares spatial econometric model. Second, we model interaction effects between agglomeration and flood-risk using a gravity-based agglomeration measure. Third, we utilise a high-resolution flood-risk measure which incorporates both flood frequency and severity. Fourth, we use a high-resolution measure of employment to capture local effects. We find that agglomeration economies have a significant mitigating effect on flood-risk. This is potentially important because it suggests that flood-risk may have a more deleterious effect on employment in areas where economic agglomeration is weak. Policy-makers, insurers and planners cannot, therefore, assume a uniform effect of future changes to flood-risk as a result of climate change, and this needs to be taken into account when estimating the costs and benefits of interventions to reduce or underwrite flood-risk at particular locations. Our model offers a robust methodological basis for such estimation.

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.