Abstract
River floodplains and reservoirs interact throughout a basin drainage
network, defining a coupled human-water system with multiple feedbacks.
Recent modeling developments have aimed to improve the representation of
such processes at regional to continental scales. However, most
large-scale hydrological models adopt simplified lumped reservoir
schemes, where an offline routine is run with inflows estimated by the
model, with limited consideration of the complementarity between
floodplains and reservoirs on attenuating floods at regional scale. This
paper presents a novel approach that fully couples
river-floodplain-reservoir hydrodynamic and hydrological models,
significantly improving the representation of reservoir dynamics and
operation in the river-floodplain-reservoir continuum at large scale and
across multiple dam cascades. The model is applied to the Paraná River
Basin with explicit simulation of 31 large dams and river hydraulic
variables at basin scale. Three types of reservoir bathymetry
representation are compared, from lumped to distributed methods,
combined with three reservoir operation schemes and varying degrees of
input data requirement within two parameterization scenarios (global and
regional setups). The operation schemes were more relevant than the
reservoir bathymetry representation to estimate downstream flows and
water levels. While the data-driven operation scheme, based on linear
regressions between observed water levels and dam outflows, provided the
best estimates of both active storage and discharges, the more generic
operation reasonably estimated discharges and peak attenuation, albeit
not as accurately for active storage. The global parameterization of
reservoir operation resulted in poorer performance compared to the
regional-based one, but it satisfactorily modeled discharge and peak
attenuation. Regarding the reservoir bathymetry representation, a basin
scale comparison of the lumped and distributed schemes indicated the
inability of the former to represent backwater effects. This was further
corroborated by validating the longitudinal water level profile of
Itaipu dam with ICESat satellite altimetry data. Finally, the model was
used to show the complementarity between floodplains and reservoirs on
attenuating floods at regional scale. Large scale models should move
beyond offline coupling strategies, and include regional-based,
data-driven reservoir operation schemes together with a distributed
representation of reservoir bathymetry into river-floodplain hydraulic
schemes. This will largely improve the estimation of river discharges,
water levels and flood storage, and thus the model ability to represent
the regional scale river-floodplain-reservoir continuum.