Satellite altimetry may be used for monitoring large rivers, such as Niger River. Since data samples are sparse in time and accuracy of measurements is limited, an interpolation method is developed in order to get water levels at any time and to adjust observed values, taking account of their limited accuracy. The method uses a flood propagation model dedicated to flood propagation in large African rivers calibrated from one gauge station, used as a reference, and satellite altimetric data provided by Topex or Envisat. It allows capturing the water level behavior at the flood peak even though no measurement was available at that time.