CHAPTER ONE
INTRODUCTION
1.1 Background of the study
flooding is among the most common and destructive natural hazards, resulting in considerable direct losses (e.g. personal injury and property damage) and increasing indirect impacts (e.g. interruption of public services and economic activities), especially in the urbanized areas around the world (e.g. Ramos et al. 2005; Mejia and Moglen 2010; Smith et al. 2012; Wright et al. 2012). Flood can be caused by heavy rain can be a regular pluvial flood by a short timescale, generally less than six hours. It is usually by their very fast evolution and occurs within minutes or a few hours of excessive rainfall (Naulin et al. 2013). There exists a broad consensus that the combined effect of climate change and rapid urbanization is generally recognized as the primary cause for more frequent, heavier rainfall-runoff (IPCC, 2013; Du et al. 2012; Suriya and Mudgal 2012; Zhou et al. 2012). Furthermore, the lack of anticipation of flooding events such as the unavailability of short-term forecasting and warning, combined with insufficient, postponed adaption measures (e.g. inadequate drainage capacity) largely limit the efficiency of urban flood risk management, leading to the enhanced consequences of these events in most cities like lagos.
Over the past several decades, the significant disasters associated with street networks and flooding events have been frequently occurring in different urban environments such as New York and London in developed countries as well as Beijing and Bangkok in developing countries (Pitt 2008; Hung et al. 2009; NYC Emergency Management 2014). Road networks in Lagos are particularly vulnerable to flooding events as the conflict between rapid urbanization and the lagging urban (infrastructure) planning is emerging onto the surface.
1.2 Statement of the Problem
In all the flood prone areas, urban road network may be the major assets affected first by inundations, which cause not only infrastructure damage but also transportation disruption, due to its low-lying nature compared to the neighborhood and high-density throughout urban territory. More seriously, almost half of the flash flood casualties involve people on flooded roads by trapping in their cars or by escaping in the rapid rise of open water (Drobot et al. 2007; Versini et al. 2010a).
Although there is a huge demand for understanding urban road network risk to Flooding, until now, very few work have attempted to systematically examine the potential effects of flooding events on urban road systems largely due to the lack of adequate data and observations concerning road flooding, difficulty in numerically modeling the PFF dynamics and the complexity of cascading effects resulting from temporary flooding on transportation systems (Suarez et al. 2005).