CoAuthors

Rodrigo PAIVA (OSU, USA); Joécila SANTOS da SILVA (UEA, Brazil); Stéphane CALMANT (IRD, France); Walter COLLISCHONN (UFRGS, Brazil); Sisouvanh KITTAVONG (LEGOS, France); Marie-Paule BONNET (IRD, Brazil); Frédérique Seyler (IRD, FRENCH GUYANA)

The Manning Equation states that the discharge Q in a river reach is given by: Q = 1/N * W * d**5/3 * s*-1, where n is the Manning coefficient, W the cross section width, d the water depth and s the surface slope. In a first experiment, we have computed a,b and z0 as Q(t) = a*[h(t)-z0]**b for a thousand of locations where series of water height h(t) were gained by the ENVISAT, Jason-2 and SARAL altimetric missions over more than 70 rivers throughout the Amazon basin. These series sample either very large reaches of the major contributors or reaches of second or even third order tributaries as narrow as a few tens of meters. The discharge series Q(t) were taken from runs of the MGB-IPH rain-discharge model. These rating curves enable the computation of a discharge as soon as an altimetric mission collects measurements at the corresponding crossing of its orbit with the river channel. Most of these rating curves have a satisfactory result of fit with Nash-Sutcliff coefficient (NS) greater than 0.7. We identifyed that some low NS coefficient were obtained at the mouth of the rivers. In a 2nd experiment, we changed the parametrization of the power law as folloging: Q(t) = a*[h(t)-z0]**b * s(t)**c. We used mean monthly slopes for s(t). NS were significantly improved in experiment 2, evidencing that the low NS in experiment 1 were due to the backwater effect. We also present how the a,b,c and z0 parameters can be related to the physical parameters entering in the Manning equation.