Flood Hazard Scenarios of the Sirba River (Niger): Evaluation of the Hazard Thresholds and Flooding Areas

Giovanni Massazza,Vieri Tarchiani,Maurizio Rosso,Maurizio Tiepolo,Elena Belcore,Gérémy Panthou,Alessandro Pezzoli,Mohamed Housseini Ibrahim,Catherine Wilcox,Theo Vischel,Paolo Tamagnone

doi:10.3390/w11051018

Abstract

In Sahelian countries, a vast number of people are still affected every year by flood despite the efforts to prevent or mitigate these catastrophic events. This phenomenon is exacerbated by the incessant population growth and the increase of extreme natural events. Hence, the development of flood management strategies such as flood hazard mapping and Early Warning Systems has become a crucial objective for the affected nations. This study presents a comprehensive hazard assessment of the Nigerien reach of the Sirba River, the main tributary Middle Niger River. Hazard thresholds were defined both on hydrological analysis and field effects, according to national guidelines. Non-stationary analyses were carried out to consider changes in the hydrological behavior of the Sirba basin over time. Data from topographical land surveys and discharge gauges collected during the 2018 dry and wet seasons were used to implement the hydraulic numerical model of the analyzed reach. The use of the proposed hydraulic model allowed the delineation of flood hazard maps as well the calculation of the flood propagation time from the upstream hydrometric station and the validation of the rating curves of the two gauging sites. These significative outcomes will allow the implementation of the Early Warning System for the river flood hazard and risk reduction plans preparation for each settlement.

Highlights

Recent years have been characterized worldwide by an increasing number of flood events and flood-related effects [1,2]
The normal condition was considered for the flow below the threshold of 600 m3 /s that correspond at the Q15 and the S-RT5 ; The frequent flood comprised the flow in the range 600–800 m3 /s where 800 m3 /s is related both to Flow Duration Curvesare (FDC) (Q5 ) and GEV analyses (S-RT10 and NS-RT2 ); The severe flood varied from 800 to 1500 m3 /s and corresponded to a flood with S-RT30 years that became a NS-RT5, a little greater than the major measured flood event of 2012; The catastrophic flood covered up to 2400 m3 /s that is the flood event with S-return time (RT) equal to 100 years
Considering increasing-attention that flooding events attract on the Sahelian countries, this research was designed to evaluate the flood exposure of the riverine population of the Sirba River

Summary

Introduction

Recent years have been characterized worldwide by an increasing number of flood events and flood-related effects [1,2]. An alarming case is the high frequency of flooding events in the Middle Niger River Basin (MNRB) during the last 20 years [3,4,5]. Sahelian rivers have shown an increase in discharge since the early 1990s leading to the catastrophic floods registered in the past. [8] highlighted that extreme floods represent a crucial issue for Sahelian countries, many researchers claimed that the increasing occurrence of extreme rainfall events and the reduced water-holding capacity of the soil are at the origin of more severe floods [9,10,11]. Since Tarhule at al. [8] highlighted that extreme floods represent a crucial issue for Sahelian countries, many researchers claimed that the increasing occurrence of extreme rainfall events and the reduced water-holding capacity of the soil are at the origin of more severe floods [9,10,11].

Methods

Results

Discussion

Conclusion