Expressive riverine fluxes over Amazon floodplain units revealed by high
resolution 2D modelling
Abstract
Water fluxes in the Amazon River floodplain affect hydrodynamic and
ecological processes from local to global scales. Nevertheless, these
fluxes remain poorly understood due to difficult access and limited
data. In this study, we characterize the hydrodynamics of eight
floodplain units of the central Amazon River (40’000
km2) using the 2D hydraulic model HEC-RAS. High
resolution modeling improved the representation of river and floodplain
discharge, water surface elevation (77 cm accuracy) and flood extent
(~80% - high water period, ~52% -low
water period). We have learned 13 lessons about river and floodplain
hydrodynamics from the modeling. The most remarkable lessons are that
the floodplain is organized in units of about 80 km with upstream inflow
and downstream outflow. These gross flows are much larger than the net
flows with values of up to 20% of the Amazon River discharge and a
residence time around 6 days during floods (several months during low
water period). Water extent does not a have strong interannual
variability during floods as the volume stored in the floodplain,
possibly due to topographic constrains. Significant flood extent and
volume hysteresis, as well as active flow and storage zones on the
floodplain, highlight the complexity of floodplain hydrodynamics.
Extreme floods strongly impact the onset and duration of the flood of up
to 2 months and, consequently, on the period of high connectivity with
the river. These findings are important for understanding carbon and
sediment fluxes, and the effects of climate change on water fluxes and
riparian communities.