Presentation on single bridge section analysis on a river reach by HEC-RAS

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.