Automating HEC-RAS input data and execution for improved hydraulic analysis: The Bolivian Amazonia 2014 flood

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Vladimir Moya Quiroga, Shuichi Kure, Keiko Udo, Akira Mano

Friday 3 july 2015

9:00 - 9:15h at Oceania Foyer (level 0)

Themes: (T) Flood risk management and adaptation, (ST) Flooding along in rivers and coasts

Parallel session: 14L. Floodrisk - Flooding

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The Bolivian Amazonia is an extent floodplain region that continuously suffers flooding from the most important Bolivian rivers. One example is the Mamore River, the longest and most important Bolivian river and one of the main tributaries of the Amazon river. Despite the importance of the river and the frequency of the floods, there are almost no studies about its flood risk. Development of a hydraulic numerical model able to simulate flood scenarios is an important step in order to perform flood risk analysis. Selection of a proper Manning roughness coefficient and boundary condition are vital steps at implementing a hydraulic model. However, such values cannot be measured and are prone to a wide range of uncertainty. Although there are some empirical suggestions, they are just suggestions and the proper values need to be calibrated. The calibration process is a time consuming one as it requires several simulations considering different values. Besides, any proposed action should be considered by modifying the model and updating the simulation. Thus, it is important to develop tools for easing the process of updating changes to a hydraulic model. This paper presents a tool developed for automating the boundary conditions and roughness input of HEC-RAS, one of the most popular hydraulic models, along with an automatization of its execution. The tool eased the task of performing a sensitivity analysis of boundary condition and roughness coefficients. Several simulations were easily performed considering several probable boundary conditions and roughness coefficients according to different criteria and suggested values. The different roughness coefficients showed that the water level may change up to 3.47 m depending on the coefficient to be used. Uncertainties from Manning roughness and boundary condition may generate differences that may propagate up to 600 km upstream. This tool proved to be a valuable tool for improving hydraulic studies considering different uncertainties. The model was then used to simulate the 2014 flood event at the Bolivian Amazonia. A Manning value of 0.035 provides good results for steady flow, and a Manning value of 0.0314 the model successfully simulates the flood event under unsteady flow condition showing the moment when the water begins to overflow and the duration of the flood. However, the model still can be improved by considering a variable Manning with values little higher than 0.035 for the low flows and values little lower than 0.029 for the high flows.