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

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.

Flood Assessment for Risk-Informed Planning along the Sirba River, Niger

“…The probability of occurrence of frequent, severe, and catastrophic rainfall is then calculated with respect to the daily precipitations recorded at the meteorological station of Gothèye The third phase firstly calculates the probability of occurrence (1/return period) of a flood according to three scenarios of fluvial and pluvial flooding (frequent, severe, catastrophic). The probability of flooding of the Sirba and the backwater of the Niger Rivers is calculated based upon the discharge recorded respectively at the stations of Garbey Kourou in the period 1956-2018 and of Niamey in the period 1929-2019 with a Generalized Extreme Values approach [23].…”

“…The area exposed to fluvial flooding according to the three hazard scenarios was identified through the hydraulic numerical model developed on the HEC-RAS software in a 1D configuration [23]. The model calculates the water surface elevations for the different discharges and extends them on the riverbed geometry.…”

Community and Impact Based Early Warning System for Flood Risk Preparedness: The Experience of the Sirba River in Niger

“…The majority (97 settlements) are distributed in riverine areas, meaning that 61,703 people, belonging to 7732 households, live in potentially flood-prone zones. The geographical framework of the study area [27]. Bossey Bangou hydrometer (BB); Garbey Kourou hydrometer (GK).…”

“…The joint impact of land degradation and extreme rainfall increase produced an extension of the drainage network and the rupture of endorheic basins that caused a further discharge increase [39]. The geographical framework of the study area [27]. Bossey Bangou hydrometer (BB); Garbey Kourou hydrometer (GK).…”

Flood Hazard Mapping Using the Flood and Flash-Flood Potential Index in the Buzău River Catchment, Romania

“…European rivers are specifically analyzed in accordance with the European Flood Directive 2007/60 and the Directive 2008/94/EC of the European Parliament and of the Council, published in the Official Journal of the European Union, whilst statistical, hydraulic and GIS techniques are used for hazard and flood mapping [4][5][6] Adaptation and mitigation have generally been treated as two separate issues, both in public politics and in practice, in which mitigation is seen as the attenuation of the cause, and studies of adaption look into dealing with the consequences of climate change [7]. Studies on the impact of climate change on flood risk are mostly conducted at the river basin or regional scale [8,9].…”