Integrated Hydrological and Hydraulic Approach for the Design of the Sorey Bridge under a Context of Climate Variability (Niamey Region, Niger)
Harouna Souley
Department of Civil Engineering, School of Mines, Industry and Geology of Niamey (EMIG), P.O.Box: 732, Niamey, Niger.
Sanda Chékaraou Mahamane Moustapha
*
Department of Discipline Didactics, Faculty of Education Sciences, Djibo Hamani University of Tahoua (UDH), PO.Box: 255, Tahoua, Niger.
Maman Hassan Abdourazakou
Department of Mines-Geology, School of Mines, Industry and Geology of Niamey (EMIG), P.O.Box: 732, Niamey, Niger.
Elhadj Daou Ibrahim
Department of Mining Engineering and Environment, School of Mines, Industry and Geology of Niamey (EMIG), P.O.Box: 732, Niamey, Niger.
Badamassi Kadri Maman Mansour
Department of Geological and Environmental Sciences, Faculty of Sciences and Techniques, André Salifou University of Zinder (UAS), PO.Box: 656, Zinder, Niger.
Laouali Idi Karimou
Department of Life and Earth Sciences (SVT), Abdou Moumouni University of Niamey (UAM), Higher Normal School, Niamey, Niger.
Lawali Idi Chamsi
Department of Geology, Groundwater and Georesources Laboratory, Faculty of Science and Technology, Bedrock and Mineral Resources Research Team, Abdou Moumouni University of Niamey (UAM), PO.Box: 10662, Niamey, Niger.
*Author to whom correspondence should be addressed.
Abstract
The increasing hydroclimatic variability observed in the Sahel poses a major challenge to the design and safety of road infrastructure exposed to flooding. This study applies an integrated hydrological and hydraulic approach to the design of the Sorey Bridge in the Niamey Region of Niger. The methodology combines precipitation-frequency analysis, GIS-based morphometric characterisation of the watershed, estimation of the 10-year flood using the ORSTOM and CIEH methods, extrapolation of the 100-year flood using the GRADEX method, and hydraulic analysis based on the Manning–Strickler relationship. The watershed covers 1,359.75 km², with a perimeter of 285.32 km and a main channel length of 50.39 km. Rainfall analysis for 1991–2000 shows marked interannual variability, with mean annual precipitation ranging from 410.7 to 816.3 mm and a maximum daily rainfall of 129 mm. The 10-year discharges estimated by ORSTOM and CIEH are 196.22 and 225.86 m³/s, respectively, giving an adopted mean design discharge of 211.04 m³/s. The GRADEX method gives a 100-year discharge of 896.78 m³/s. Hydraulic analysis yields a flow depth of 3.40 m, a mean velocity of 2.90 m/s, and a backwater rise of 0.208 m. Total pier scour is 3.86 m. The proposed protection comprises 0.74-m-diameter riprap, with a 3.00-m width and 2.22-m layer thickness, together with a 2.00-m freeboard. These parameters support the hydraulic design of the Sorey Bridge under extreme flood conditions.
Keywords: Climate variability, 10-year flood, 100-year flood, hydrology, bridge hydraulics, scour