HEC-RAS tutorial on single bridge
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This document discusses using HEC-RAS software to analyze a river reach containing a single bridge. It outlines the input data needed, including geometric data and flow data. It then describes the steps to model the bridge, including adding the bridge, defining the geometry, and selecting modeling approaches. The document compares results from modeling the bridge as a pressure/weir and using the energy method. It notes that adjustments to contraction/expansion coefficients and cross section locations can improve results.
HEC-RAS tutorial on single bridge
- 1. Prepared By Group 10 Salma Nasrin Siddique 0916008 Nazia Hassan Choudhury 0916010 Nureen Faiza Anisha 0916011 Course no. WRE 404 Course name: Computer Application in Water Resources Engineering Level/Term: 4/1 Dept. of Water Resources Engineering, BUET.
- 2. Introduction Overview Methodology Notes and recommendations
- 3. HEC-RAS can be used to analyze a river reach that contains a single bridge crossing. This presentation demonstrates the procedure of analyzing a river reach that contains a single bridge of simple geometry and that stands perpendicularly to the flow.
- 4. Input : Geometric Data + Flow Data Plan 01 High Flow Method as press/weir Plan 02 Energy Method for High FlowAnalysis Review of Results Adjustment of Contraction and Expansion Reach Lengths New Plan Energy Method for High Flow Analysis New Plan High Flow Method as press/weir Comparison of Results
- 5. Open HEC-RAS Software File Open Project Destination Folder Desired Project (.prj format)
- 6. 1. River System Schematic 2. Cross Section Geometric Data 3. Bridge Geometry Data 4. Ineffective Flow Areas 5. Bridge Modeling Approach 6. Steady Flow Data
- 9. Options Add bridge/Culvert Define station number Deck/Roadway Editor Input Data Pier Input Data
- 10. Geometric Data Editor Cross-section Options Ineffective Flow Area
- 11. Geometric Data Editor Bridge/Culvert Icon Bridge Modeling Approach Select Methods and enter Coefficient of Discharge
- 12. Main Program window Edit Steady Flow Data Steady Flow Data Editor Input boundary conditions and discharge
- 13. Steady Run icon (main program window) Steady Flow Analysis Option Critical depth output Plan Define New plan and Short ID Compute Note: We run p/w as plan 01 We run energy method as plan 02
- 14. View profile icon (main program window) Options Plans Select desired plans
- 16. Contraction Length Expansion Length Fc2 : Main channel Froud number at section 2 Fc1 : Main channel Froud number at section 1 Qob : The overbank flow at section 4 Q : The total flow at section 4 nob : The manning’s coefficient for overbank at section 4 nc : The manning’s coefficient for main channel at section 4 Lobs : The average length of bridge obstructions
- 17. One dimensional model can predict only one resulting water surface, therefore, the fluctuations along the cross section will NOT occur in the HEC-RAS model as they do during the actual event. Hence, there will be some errors. If the observed data are already in collection, the water surface profiles calculated by the model can be calibrated with help of it if necessary. The locations of the cross sections and the values selected for the expansion and contraction coefficients in the vicinity of the bridge are crucial for the accurate prediction of the energy losses through the bridge structure. Hence adjustments yield better results.