Design Floods in Taza city by using hydrologic and hydraulic modeling (Taza, Morocco)

Abstract:

Morocco, is like the rest of the world, suffers from the floods problems. These problems necessitate a good knowledge of the spatiotemporal variability of the hydrological regime of rivers (floods and low flows) in order to achieve a flood management in watershed and in floodplains. This study looks at the phenomenon of extreme floods of Larbaâ River. These overflows, having occurred in recent years, especially during the years 2000, 2002 and 2010, caused casualties and material damage. For this reason, the Larbaâ watershed, which expands largely on the pre-Rif area, has been the subject of hydrologic and hydraulic modeling to characterize and assess the flood risk in Taza city. The study of the creation and evolution of this risk is based on the determination of factors contributing to flooding events. For this purpose, the study is interested in the estimation of design floods, hydraulic modeling and flood management. In our case, we have used the Gradex method because of the lack of the daily stream flow data that can facilitate the statistical analysis of ancient floods. The study is based on long series of observations (49 years) of the annual maximum daily rainfall, and the Intensity-Duration-Frequency curves of the raingauge station of Taza. The transformation of rain into flow discharge is one of the main problems facing the hydrologists. For this reason the hydrologists have been looking to find the relation (rainfall-flow) by developing multiples empirical models to simulate this physical phenomenon. This is why we have used the Caquot model with which we can calculate the flow with the exceeding frequency f. In other hand, we have used the hydraulic modeling in order to know the flood risk along the studied sections, and to determine the floods impact of different return periods: 10 years, 20 years, 50 years, etc.. This approach aims to predict numerically the spatiotemporal evolution of hydraulic properties during a flood.Therefore, the hydraulic simulation on the study area allowed us to obtain information about the extensions and heights of floodwater at different points and for different frequencies. This study is considered as guide for flood hazard mapping. Otherwise, the hydraulic results can be used as basis for Taza public infrastructure department, railway department, architecture, and engineering.