The study of flood risk involves the knowledge of the spatial variability in the characteristics of the vegetation cover, terrain, climate and changes induced by the intervention of humans in watersheds. The increased needs of the actors in land management mean that static maps no longer meet the requirements of scientists and decision-makers. Access is needed to the data, methods and tools to produce complex maps in response to the different stages of risk evaluation and response. The availability of very high spatial resolution remote sensing data (VHSR) and digital terrain model (DTM) make it possible to detect objects close to human size and, therefore, is of interest for studying anthropogenic activities. The development of new methods and knowledge using detailed spatial data, coupled with the use of GIS, naturally becomes beneficial to the risks analysis. Indeed, the extraction of information from specific processes, such as vegetation indices, can be used as variables such as water heights, flow velocities, flow rates and submersion to predict the potential consequences of a flood. The functionalities of GIS for cartographic overlay and multi-criteria spatial analysis make it possible to identify the flood zones according to the level of risk from the flood, thus making it a useful decision-making tool.This study was carried out on the territory of watersheds in the Annaba region, East of Algeria. The choice was guided by the availability of data (satellites images, maps, hydrology, etc.) and hydrological specificities (proximity to an urban area). The adopted model is divided into two parts. The first part is to establish a methodology for the preservation of wetland biodiversity and the protection of urban areas against floods. Thanks to the multi-criteria spatial analysis and the functionalities of the GIS, we established a flood risk map for the watershed defined above. The result was satisfactory compared with the field reality. The second part of the model consisted of the integration of cadastral information with the flood risk map obtained in the first part of our research.The primary objective of this mapping is to contribute to the development of flood risk management plans (in the sense of risk reduction). The mapping stage also provides quantitative elements to more accurately assess the vulnerability of a territory.
Floods are frequent hazard in Algeria. They cause severe casualties, destroy infrastructures, and impair economies. In the past decades, Algeria experienced devastating floods. The dominant type of occurring floods are flash floods, which tend to be not well documented and studied in Algeria. This chapter presents a brief introduction to the flood phenomena within the Algerian climatic and management context, based on databases, scientific publications, and local technical reports. Existing studies about floods are reviewed. It also provides an analysis of the most disastrous floods that occurred in the past decades. Of the most noteworthy flash floods, a highlight of the Bab El Oued flash flood occurring in a heavily urbanized setting and the M’zab Valley flash flood, which took place in a UNESCO World Heritage Site. The monitoring network in Algeria is presented and data availability is discussed. The implementation of the first forecasting and early warning system are also presented. Different aspects of flash floods were presented including the effect of the increase of urbanization, the influence of climate change and the adopted strategies of flood risk management. Heavy and increasing urbanization and population growth increased the flood vulnerability and this trend must be mitigated.
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