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Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/nhess-2019-168
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/nhess-2019-168
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 05 Jun 2019

Submitted as: research article | 05 Jun 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Natural Hazards and Earth System Sciences (NHESS).

Modeling the effects of sediment concentration on the propagation of flash floods in an Andean watershed

María Teresa Contreras1,2,3 and Cristián Escauriaza1,2 María Teresa Contreras and Cristián Escauriaza
  • 1Departamento de Ingeniería Hidráulica y Ambiental, Pontificia Universidad Católica de Chile. Av. Vicuña Mackenna 4860, 7820436, Santiago, Chile
  • 2Centro de Investigación para la Gestión Integrada de Desastres Naturales (CIGIDEN), Chile
  • 3Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, IN, 46556, USA

Abstract. Rain-induced flash floods are common events in regions near mountain ranges. In peri-urban areas near the Andes the combined effects of the changing climate and ENSO have resulted in an alarming proximity of populated areas to flood-prone streams, increasing the risk for cities and infrastructure. Simulations of rapid floods in these watersheds are particularly challenging, due to the complex morphology, the insufficient hydrometeorological data, and the uncertainty posed by the variability of sediment concentration. High concentrations produced by hillslope erosion and rilling by the overland flow in areas with steep slopes and low vegetational covering can change significantly the dynamics of the flow as the flood propagates in the channel. In this investigation, we develop a two-dimensional finite-volume numerical model of the non-linear shallow water equations coupled with the mass conservation of sediment to study the effects of different densities, which include a modified version of the quadratic stress model to quantify the changes on the flow rheology. We carry out simulations to evaluate the effects of the sediment concentration on the floods in the Quebrada de Ramon watershed, a peri-urban Andean basin in central Chile. We simulate a confluence and a total length of the channel of 10.4 km, with the same water hydrographs and different combinations of sediment concentrations in the tributaries. Our results show that the most important effects on the flood propagation are observed in the range of concentrations from 0 % to 20 %. Simulations also show that variables such as the arrival time of the peak flow, and the shape of the hydrograph at different locations along the channel are not significantly affected by the sediment concentration and depend mostly on the steep channel morphology. Through this work we provide a framework for future studies aimed at improving hazard assessment, urban planning, and early warning systems in urban areas near mountain streams with limited data and affected by rapid flood events.

María Teresa Contreras and Cristián Escauriaza
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María Teresa Contreras and Cristián Escauriaza
María Teresa Contreras and Cristián Escauriaza
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Short summary
In this investigation we study the effects of high sediment concentrations on the dynamics of flash floods in mountain regions, with an application to a river in the Andes that has produced catastrophic events in the city of Santiago, Chile. We develop an advanced computational model to understand the effects of floods with high sediment loads on steep channels. These new insights can be used to design early warning systems and contribute to urban planning in cities near mountain rivers.
In this investigation we study the effects of high sediment concentrations on the dynamics of...
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