River-floodplain interaction and flood wave routing along rivers flowing through Pantanal wetlands

Abstract

The Pantanal is the largest tropical wetland in the world and has extraordinary biodiversity, being considered of great ecologic value. Besides the intimate dependence of Pantanal ecosystems, functioning, and integrity on water dynamics, the flood pulse and inundation also regulate traditional riverside communities’ way of life, recreational fishing tourism, jaguar tourism, cattle raising, navigation, and agriculture. This study advances in characterizing flood wave dampening, flood wave travel time, and lateral exchanges of water of rivers flowing along the Pantanal, investigating the relationship between these characteristics and the upstream flood. A dynamically coupled 1D-2D hydrological modeling approach, already calibrated on earlier work is used, to simulate the main channel flood wave routing, water inundating and moving across the floodplain, and channel-floodplain bidirectional interaction. Four upstream flooding scenarios were imposed, simulating contributing floods from uplands (Planalto), that enter and flow along each of the major rivers of the Pantanal region. The results indicate that flood wave travel time is directly related to the size of the upstream flood, but the presence of secondary peak flows before or after the major flood peak did not have a marked influence. Patterns of reduction or increase in peak flow along the river reaches were also identified, which were independent of the size and shape of the upstream flooding condition. For the uppermost reaches of all rivers, the loss of water from the main channel to the floodplain heavily attenuates the flood hydrograph. This flood dampening showed to be stronger for larger floods, as there is more proportion of channel flow spilling over to the floodplains. However, in absolute terms, these results showed that upstream floods of different sizes or with different shape characteristics (multiple or single peak flows) present quite similar flood hydrographs as one moves downstream along the Pantanal region, becoming typically unimodal smoothed flood hydrographs.