On the discretization of river networks for large scale hydrologic-hydrodynamic models

Fernando Mainardi Fan,Rodrigo Cauduro Dias De Paiva,Vinícius Alencar Siqueira,Ayan Santos Fleischmann,Walter Collischonn,Paulo Rógenes Monteiro Pontes,João Paulo Fialho Brêda

doi:10.1590/2318-0331.262120200070

Fernando Mainardi Fan, Rodrigo Cauduro Dias De Paiva + Show 5 more

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https://doi.org/10.1590/2318-0331.262120200070

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Abstract

ABSTRACT The discretization of river networks is a critical step for computing flow routing in hydrological models. However, when it comes to more complex hydrologic-hydrodynamic models, adaptations in the spatial representation of model calculation units are further required to allow cost-effective simulations, especially for large scale applications. The objective of this paper is to assess the impacts of river discretization on simulated discharge, water levels and numerical stability of a catchment-based hydrologic-hydrodynamic model, using a fixed river length (Δx) segmentation method. The case study was the Purus river basin, a sub-basin of the Amazon, which covers an area that accounts for rapid response upstream reaches to downstream floodplain rivers. Results indicate that the maximum and minimum discharges are less affected by the adopted Δx (reach-length), whereas water levels are more influenced by this selection. It is showed that for the explicit local inertial one-dimensional routing, Δx and the α parameter of CFL (Courant-Friedrichs-Lewy) condition must be carefully chosen to avoid mass balance errors. Additionally, a simple Froude number-based flow limiter to avoid numerical issues is proposed and tested.

Highlights

Hydrological models are a set of mathematical equations designed to represent components of the hydrological cycle, allowing for the understanding of its processes and many other applications, for instance, the assessment of land use and climate change impacts (Sorribas et al, 2016; Bravo et al, 2014; Nóbrega et al, 2011) or operational flood and drought forecasting (Alfieri et al, 2013; Sheffield et al, 2014; Fan et al, 2015)
While simplified physical approaches are known to be suitable for flow routing in steep terrains (Price, 2018), and yet adopted by most of current global hydrological models (Bierkens, 2015; Kauffeldt et al, 2016), complexities emerging from river-floodplain water exchange in mild slopes can lead to flood peak delay and backwater effects on tributaries, which cannot be resolved with simple flow routing methods (Trigg et al, 2009; Yamazaki et al, 2011; Paiva et al, 2011; Fleischmann et al, 2016; Lopes et al, 2018; Zhao et al, 2017)
Despite the larger number of unit-catchments and river reaches in the 5 km (3064) in comparison to the 50 km (400) threshold, the catchment border between tributaries is maintained equal since the resulting irregular grid follows the underlying topography

Summary

Introduction

Hydrological models are a set of mathematical equations designed to represent components of the hydrological cycle, allowing for the understanding of its processes and many other applications, for instance, the assessment of land use and climate change impacts (Sorribas et al, 2016; Bravo et al, 2014; Nóbrega et al, 2011) or operational flood and drought forecasting (Alfieri et al, 2013; Sheffield et al, 2014; Fan et al, 2015). Modeling large scale river hydrodynamics can be very challenging, since many of the world largest floodplains occur in ungauged or poorly monitored areas, such as the Amazon, Congo, Niger and Paraguay rivers (Paz et al, 2011; Pedinotti et al, 2012; Paiva et al, 2013; Tshimanga & Hughes, 2014)

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