Flood risk mapping using multi-criteria analysis (MCA) through AHP method case of El-Ham wadi watershed of Hodna basin (Algeria)

Following the rapid increase in flood events in recent years, flood risk assessment and mitigation have become a necessity. The purpose of this study is to develop updated and accurate flood risk and hazard maps in the El-Ham watershed within the large Hodna basin (Algeria). In order to achieve this objective and to select weights of contributing criteria to flood risk, geographical information system and multi-criteria analysis along with the application of analytical hierarchy process technique have been used. Factors considered to be the cause of flooding are slope, annual maximum daily precipitation, drainage density, elevation, land use/cover and soil type. In addition to the hazard, population density has been also used to determine the risk of flooding in El-Ham watershed. The percentages of weights obtained for each parameter are 39% for slope, 25% for drainage density, 18% for rainfall, 9% for elevation, 6% for land use/cover and 3% for soil type. For validation of these weights, a consistency ratio is then calculated. Main outcomes present a high flood potential, especially in the North-Eastern, North-Western and Central part of the study area. However, this high potential decreases further when one goes toward the South. This research suggests that the chosen criteria are sufficient to obtain a reliable and simplified flood risk map. Any additional parameters would add more details to the risk map using hydraulic and/or hydrological models to generate flood hazard maps such as RRI and HEC-RAS models.