Analysis of flow, roughness and downstream boundary condition uncertainties within HEC-RAS 1-D modeling

Date

2024-1-19

Author

Budak Balta, Başak

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A hydraulic model is a mathematical representation used to simulate the behavior of water flow in natural systems, such as rivers or engineered structures, such as channels, and drainage networks. These models help in predicting variables like flow rates, water levels, and velocities under various conditions. Digital Elevation Models (DEMs), hydrological assessments (Intensity-Duration-Frequency (IDF) curves, hydrographs), roughness coefficients and boundary conditions are main inputs for hydraulic models and they influence the accuracy of the simulations. Uncertainties in input parameters can affect the precision of the model's predictions. In this study, four different scenarios were implemented by assigning appropriate probability distribution functions to the input values of Manning roughness coefficient, inflow (steady state discharge), and known water surface elevation as the downstream boundary condition. The study was carried out and modeled using an automated Monte Carlo-based approach with using HEC-RAS and Visual Basic Applications software in the Kargıcak River watershed in Alanya, Antalya. When examining the results, it is observed that the variation in the downstream boundary condition affects the water level in the sections within 200 meters of the outlet in the downstream region of the stream and the water level at the structures (e.g. bridges). When the uncertainties in steady state discharge and Manning roughness coefficient values are also included as uncertainties, the most critical situation is observed to occur when these parameters are entered at their maximum values.

Subject Keywords

Hydraulic models, Uncertainties, Probabilistic flood modeling

URI

https://hdl.handle.net/11511/108395

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Graduate School of Natural and Applied Sciences, Thesis