The present chapter describes an end-to-end methodology for assessing flood protection strategies, including the whole methodological process from hydrological statistics to detailed 2D hydraulic modelling, damage calculation and flood risk evaluation. This risk-based approach serves as a component of a decision-support system (DSS) developed in Belgium for identifying cost-effective flood management strategies in the context of climate change. The DSS accounts for both hydraulic and socio-economic parameters to quantify the benefits (in terms of avoided risk) and the cost of each strategy. Besides reviewing fundamentals of flood risk assessment, including the inundation model and main concepts related to flood risk, a consistent methodology for micro-scale flood risk analysis is presented in detail, combining complementary sources of GIS information such as high resolution and high accuracy land use database as well as socio-economic datasets. Finally a case study on a main tributary of river Meuse in Belgium is described.
TopIntroduction
For centuries people have settled in areas nearby rivers. They exploited rivers for many purposes, such as inland navigation, fishery, irrigation in dry regions or electricity production. They also had to face inundation events but, to a certain extent, they adapted their settlements and their behaviour to cope with this hazard. Flood occurrence and the consequences of flooding were generally accepted by society.
Nowadays, riversides are becoming more and more urbanized but the communities living along rivers tend not to accept the risk of flooding any longer. Drastic reductions in flood risk are requested. Moreover, within the framework of climate change, heavy precipitations are expected to increase in terms of frequency and intensity (IPCC 2001). In this context, it is reasonable to think that peak discharges in rivers will also rise and such events will become more frequent. Thus, protection of people threatened by flooding and integrated flood risk management are becoming issues of growing importance.
At present, the design and the optimization of flood protections is gradually shifting from a method based on a single return period to a full risk analysis, which takes into account a large range of occurrence probability (Merz 2006). This type of approach may lead to cost benefit analyses, for which predicted losses are estimated from the risk analysis procedure. This chapter is in line with the framework of this emerging approach for elaborating flood management strategies. Indeed, the procedure detailed in this chapter relies on a risk modelling chain handling the data flow from statistical analysis of river flows to the risk evaluation. This risk modelling system enables to assess psycho-social impacts of floods as well as direct and tangible economic losses, with the aim of designing and optimising local flood protection strategies.
While most risk analyses are performed at macro- or meso-scale, in this chapter an original micro-scale analysis is described. It means that each asset (house, company, public building …) is analyzed individually. Such a refined investigation leads to detailed economic as well as psycho-social damage evaluations which prove to be helpful to rank different adaptation measures (e.g. mobile dikes, rehabilitation of floodplains, diversion channel …) in terms of overall effectiveness.
The developed tool also handles a large number of detailed and accurate input data necessary in such a micro-scale analysis. First, 2D flow modelling is essential for providing as an output high resolution flood maps detailing the distribution of water depth and flow velocity in the floodplains and representing interactions between main channel and floodplains. Secondly, accurate land use databases have to be used in order to identify each building individually and for determining their type (residential, industrial, petrol station …).