Study region: The Niger River basin (NRB) at Niamey, West Africa. Study focus: Two approaches to estimate the cross-section of rivers based solely on satellite im-agery (or digital elevation model, DEM) and altimetry for a large data-deficient region are pro-posed. These approaches are the "lateral-method" (LM), which directly provides the cross- sections, and the mixed method (MM), which incorporates a DEM with topography/bathyme-try. The LM consists of following the river water lateral evolution on either side of a centerline using daily Planet Scope imagery, while the riverbed is estimated using satellite altimeters. The MM is based on the riverbed estimated from altimetry during the recession period, and the banks’ heights are extracted from a DEM. River discharge was estimated at four cross-sections over a reach of 30 km at Niamey. An evaluation of the estimated discharge using in-situ discharge at Niamey hydrometric station presents a Nash-Sutcliffe efficiency of 0.93 and a relative bias of 3.3 %. New hydrological insights for the region: The proposed method is feasible for other rivers in the Sahelian zone and supports a better understanding of surface water hydrology. For example, the estimated discharge at four cross-sections at a river reach of 30 km at Niamey was used to observe downstream flow gains. Nevertheless, the role of uncertainties and other contributions (e.g., evaporation losses) on the observed gains deserves further investigation.