CoAuthors

Stéphane CALMANT (IRD, France); Jérome MONNIER (INSA, France); Joécila SANTOS da SILVA (UEA, Brazil); Adrien PARIS (LEGOS, France); Rodrigo PAIVA (OSU, USA); Sylvain BIANCAMARIA (CNRS, France)

Hydrodynamic laws predict that irregularities in a river bed geometry produce spatial and temporal variations in the water level, hence in its slope. Conversely, observation of these changes is a goal of the SWOT mission with the determination of the discharge as a final objective. In this study, we analyse the relationship between river bed undulations and water surface on the Xingu river, a tributary of the Amazon river. It is crosscut more than 10 times by a single ENVISAT track over a hundred of km. We have determined a time series of water levels, hence slopes, at each of these crossings, call virtual stations (VS). Using the discharge series computed by Paiva et al. (2013) between 1998 and 2009, Paris et al. (in press) determined at each VS a rating curve relating these simulated discharge with the ENVISAT height series (see the poster by Paris et al.). One parameter of these rating curves is the zero-flow depth z0. We show that it is possible to explain the spatial and temporal variations of the slope in terms of hydrodynamical response of the longitudinal changes of the river bed geometry given by the successive values of z0. Our experiment is based on realistic values for the Manning coefficient and river widths picked up on Landsat and JERS images. We confirm that the hydrodynamical signature of the flow runing in the river is consistent with the height and slope information gained by satellite altimetry. These hydrodynamical signatures are more visible when the river bed geometry varies significantly, at control sections, for instance. Therefore, this study suggests that the longitudinal variations of the slope might be an interesting criteria for the segmentation of rivers into elementary reaches for the SWOT mission.