Post on 30-Jan-2018
HEC-RASAN INTRODUCTION
Patrick Ndolo Goy & Dr. Pierre Y. Julien
PRESENTATION
US Army Corps of Engineers (USACE)
Hydrologic Engineering Center
River Analysis System
http://www.hec.usace.army.mil/software/hec-ras/
OVERVIEW OF CAPABILITIES
Four one-dimensional river analysis components:
o Steady flow water surface profile computations o Unsteady flow simulationo Movable boundary sediment transport computationso Water quality analysis+o Several hydraulic design features
Computational Procedure - basic equations One-dimensional Energy Equation
Continuity EquationZ: elevation of the bottom
of the channelY: elevation of the water
surfaceV: flow velocity: coefficientg: gravityhe: head lossesA: area of cross section
Computational Procedure - basic equations
Equation of Resistance to flow Manning Equation
Q: flown: Manning’s coefficientA: area of cross sectionRH: hydraulic radiusSf: friction slopeP: Wetted perimeterK: Conveyance
/ / / /
Computational Procedure - basic equations
energy losses friction - Manning Equation contraction/expansion - loss coefficient
L: Reach length
Sf: Friction slope
V: flow velocity
: coefficient
g: gravity
he: head losses
A: area of cross section
C: Contraction/expansion coefficient
Computational Procedure - basic equations
Direct Step Method
Y: elevation of the water surface
V: flow velocity: coefficientg: gravitySf: friction slopeS0: bottom slope
∆
Main Assumptions for 1-D Steady Flow Computations Constant velocity and horizontal water surface across a channel section All flow are gradually varied with hydrostatic pressure prevailing Channel boundaries are fixed
Computational Procedure
Water surface at a given cross section computed by iteratively solving 1-D energy equation and he = hL + h0
Step 1: Assume initial value for WS elevation Assume a water surface elevation at the upstream cross section if a
supercritical profile is being calculated Assume a water surface elevation at the downstream cross section if a
subcritical profile is being calculated Step 2: Determine the corresponding total conveyance and velocity
head Step 3: Compute S and solve for he
Step 4: Solve 1-D energy equation for WS elevation Step 5: Compare WS elevation from Step 1 and 4. Iterate until values
within 0.01 feet or user-defined tolerance.
Basic data requirements –Steady Flow Simulation
Geometric Data River system Schematic Cross Section Geometry Levees, Obstructions Reach Lengths
Energy Loss coefficients Manning’s n Contraction and Expansion Coefficients
Steady Flow Data Flow Regime Boundary Conditions Discharge information
Organizational Structure
Run File (Simulation)
Output File (Results from Simulation)
Example - Application
Starting a New Project
Example - Application Entering Geometric Data
Drawing the Schematic of the River System
Tributary
0.2
0.1
0.0
Upper Reach
10
9.9
9.8
Lower Reach9.7
9.6
9.5
Sutter
River StationsRiver StationsNumeric labels increase upstream
Example - Application Drawing the Schematic of the River System
Example - Application
Cross Section Data
Example - Application
Cross Section Data
- Cross section coordinates
- Downstream Reach Lengths
- Manning’s n Values
- Main channel Bank stations
-Contraction/Expansion Coefficients
- Click on Apply Data to save data
Example - Application
Cross Section Data (Visualization) Visually inspect the section
Example - Application Entering Junction Data
Junction
- Select the computation Mode (Energy equation or Momentum Equation)
Saving the Geometry Data (File Menu of the Geometric Data window)
Example - Application Entering Steady Flow Data
Tributary
0.2
0.1
0.0
Upper Reach
10
9.9
9.8
Lower Reach9.7
9.6
9.5
Sutter
River StationsRiver StationsNumeric labels increase upstream
Example - Application Entering Steady Flow Data
Tributary
0.2
0.1
0.0
Upper Reach
10
9.9
9.8
Lower Reach9.7
9.6
9.5
Sutter
River StationsRiver StationsNumeric labels increase upstream
- Enter the number of profiles (3 profiles in this example: 10-year, 50-year and 100-year flow discharge obtained from a frequency analysis of recorded flow data from gage stations)
- Enter the flow data from upstream to downstream for each reach
- It is assumed that flow doesn’t change between X-sections (flow remains constant until another flow value is encountered within the reach)
Example - Application
Entering Boundary Conditions Necessary to establish the starting water surface at the ends of the river system
Subcritical flow regime boundary conditions only required at the downstream ends of the river system (downstream control)
Supercritical flow regime boundary conditions only required at the upstream ends of the river system (upstream control)
Mixed flow regime boundary conditions required at all open ends of the river system
Example - Application Entering Boundary Conditions
In this example, it is assumed that the flow is subcritical throughout the river system
Only boundary condition are enteredTributary
0.2
0.1
0.0
Upper Reach
10
9.9
9.8
Lower Reach9.7
9.6
9.5
Sutter
River StationsRiver StationsNumeric labels increase upstream
- “Normal Depth” button is used to define the boundary condition for the downstream end of Fall River, Lower reach (Value of 0.0004 ft/ft is entered as average energy slope)
Example - Application Performing the Hydraulic Calculations
- A plan is unique combination of:
- Geometry File (reach network, X-Sections and Junctions), and
- Steady Flow File (flows and boundary conditions)
Example - Application Viewing Graphical and Tabular Results
Cross sections
- Water surface profile (Hydraulic Grade Line) in blue
- Energy Grade Line in green
Example - Application Viewing Graphical and Tabular Results
Water Surface Profiles (“Profile Plot” button)
Example - Application Viewing Graphical and Tabular Results
Rating curve (Water Surface Elevation vs Discharge curve) at a given section
Example - Application Viewing Graphical and Tabular Results
X-Y-Z Perspective Plots
Example - Application Viewing Graphical and Tabular Results
Tabular Results
Cross Section Output
Energy grade line elevation (ft)
Velocity head (ft)
Water surface elevation (ft)
Critical Water surface elevation (ft)
Slope of the energy grade line (ft/ft)
Total discharge (cfs)
Top width (ft)
Total velocity (ft/s)
Maximum channel depth (ft)
Total conveyance (cfs)
….
Example - Application Viewing Graphical and Tabular Results
Tabular Results
Profile Output Table
Energy grade line elevation (ft)
Velocity head (ft)
Water surface elevation (ft)
Critical Water surface elevation (ft)
Slope of the energy grade line (ft/ft)
Total discharge (cfs)
Top width (ft)
Total velocity (ft/s)
Maximum channel depth (ft)
Total conveyance (cfs)
Flow area
Other Applications Bridge/culvert Modeling
Other Applications Bridge/culvert Modeling
Other Applications Inline Structures (Dams, Weirs and Gated Spillways)
Breached dam Gated Spillways
Other Applications Lateral Structures(Weirs, Gated Spillways, Culverts, and Diversion Rating Curves)
Other ApplicationsFlood management and flood insurance studies to evaluate floodway encroachments
THANK YOU!QUESTION?