HEC-RAS Training Course Aug-2009 University of Engineering and Technology Lahore
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RELEVANCE POINT Relevance Point is an engaged value added IT Solutions, Electronic equipment and Software Distribution, Training and Consulting Company. Our deep industry knowledge enables us to provide clients with optimal and innovative ideas that help them improve productivity. We deliver on our commitments, so clients can achieve profitable growth and win in the marketplace.
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• Rele Releva vanc nce e Poi Point nt is an auth author oriz ized ed rese resellller er for for Mathworks, Mathworks, AutoDesk, Sperian, Sperian, Boss International, International, Sun-Tech and a myriad of other manufacturers. Relevance Point also offers consultancy in the ICT, Finance and Marketing and Product development domains to its valuable customers.
• BOSS International provides the most powerful, comprehensive engineering software on the market today including HEC-RAS, RiverCAD, WaterNET and etc. • At BOSS International, it is 100% committed to supporting its customers—making certain that they are staying productive using its products in their work. That is our number one goal as a company.
Partnership • Boss International Inc. and RELEVANCE POINT have established a very strong relationship over the past two years. • Boss International Inc. has authorized RELEVANCE POINT to resell all proprietary and non-proprietary Boss International software products in Pakistan. • Boss International Inc. will extend full technical and warranty support to all customers of RELEVANCE POINT.
Country Licenses of Advanced Design Software’s for Teaching and Training in Engineering Institutions • The HEC has appointed RELEVANCE POINT for the Procurement of Country Licenses and training of “HEC-RAS” Software on perpetual basis for universities / degree awarding institutions.
• In the Phase-I of this project, RELEVANCE POINT has successfully completed the installation of “HEC-RAS” in June, 2009.
Country Licenses of Advanced Design Software’s for Teaching and Training in Engineering Institutions
• The details of the universities where the installation is done are:
University of Engineering & Technology, Taxilla. 02 Licenses
University of Engineering & Technology, Lahore.01 License
Mehran University of Engineering & Technology, Jamshoro. 01 License
NED University of Engineering & Technology, Karachi. 01 License
Country Licenses of Advanced Design Software’s for Teaching and Training in Engineering Institutions
• Now in Phase-II of the project, RELEVANCE POINT has scheduled to conduct training of “HEC-RAS” at NEDUET-Karachi,
on August 17-18, 2009
UET-Lahore
on August 28-29, 2009
Training Course Water Surface Profile Modeling Using HEC-RAS
HEC-RAS Training Course Aug-2009 University of Engineering and Technology Lahore
Training Objectives
Understand water surface profile modeling with HEC-RAS
Develop confidence in application of HEC-RAS to a variety of problems
Learn basic modeling techniques
Learn how to review analysis results
Learn how to troubleshoot model
Course Contents DAY-1
Introduction to HECRAS
HEC-RAS Modeling Capabilities
A brief on Governing Equations
Understanding of Geometry data / Boundary Conditions
Understanding of HEC-RAS Menu
Understanding of Outputs
Steady Flow Analysis of a simple river reach
Practice session / Discussions
Modeling a tributary /Junctions
Understanding of Ineffective flow areas / Levees
Understanding of flow Obstruction
Unsteady Flow Analysis of a simple river reach
Practice session / Discussions
DAY-2
Course Contents
Modeling a Bridge
Modeling a Culvert
Modeling Multiple Openings
Practice session / Discussions
Modeling an Inline structure (Weir, Dam etc.)
Modeling Storage Area
Modeling Bridge Scour
Modeling Channel Modifications
Understanding of notes/warnings and errors
Understanding Model Stability
Trouble shooting
Practice session / Discussions
What Should You Know?
Basic Understanding of River Hydraulics
The More hydraulic Modeling you have done the better, but not considered a prerequisite
Basic Computer Operations
Training will focus on HEC-RAS as a hands on tool for hydraulic modeling- not mathematical theory
HEC-RAS History
Developed by Hydrologic Engineering Centre – A division of Institute of water Resources (IWR), U.S Army Corps of Engineers
HEC-2 program developed in 1962-First public release in 1968
Last version 4.6.2 released in 1991
“Next Generation” Software Development begins 1990 on RAS, HMS, and other models
Started under UNIX, then shifted to MS Windows & Visual Basic RAS – River Analysis System
First released in August 1995 Version 2.0 released in July 1997 Version 2.2 released in July 1999 Version 3.0 released in January 2001 Version 3.1 released in January 2003 Version 3.1.1 released in May 2003
Version 3.1.3 released in May 2005
Common Practical Problems
How to compute Backwater Curves ? Where they are used ?
How to compute Rating Curves ? Where they are used ?
How an obstruction such as bridge, culvert, spillway and weirs effects floodplain
How to compute flow velocity/ water depth at a particular location ?
At what location flow regime ( Critical or Subcritical ) changes ?
How to compute flood extents ? What is its application ?
How can a levee/embankment effects water extents ?
For a given flood peak what is the corresponding maximum water level ?
How much water level would rise if the spillway gates fails to operate ?
HEC-RAS Capabilities
1-Dimensional steady and unsteady flow analysis software
Capable of modeling subcritical, supercritical and mixed flow regimes water surface profiles
Models complex bridges and culverts (including multiple openings)
Computes flood plain encroachments
Models channel modification
Models Bridge Scour
Models water control structures ( weir, dams, gated spillways)
Models Lateral Structures
Models Levees (Embankments/Bunds)
Models Storage Areas
Models Dam Break Studies
Models flood wave propagation
Models Multiple river networks
Flow Classification
Classification by Time
Steady Flow – Constant Flow Rate Unsteady Flow – Changing Flow Rate
Classification by Distance Uniform Flow – Characterized by constant depth and constant mean flow velocity Non-uniform Flow – Characterized by varying depth and constant mean flow velocity ( In most Practical Cases)
Flow Types
Man Made Channel
Natural Channel
Governing Equations Energy Equation
Gradually Varied Flow Computations involve solution of one dimensional energy equation Water surface profiles are computed from one cross section to the other using Iteration method/ standard step method Computational procedure …..
The energy equation is only applicable to gradually varied flow situation
Computation Procedure 1. Assume water surface elevation at upstream/ downstream cross-section 2. Based on the assumed water surface elevation, determine the corresponding total conveyance and velocity head using Manning’s Equation 3. With values from step 2, compute and solve equation for he. 4. With values from steps 2 and 3, solve energy equation for WS2.
WS2 = WS1 +
5. Compare the computed value of WS2 with value assumed in step 1; repeat steps 1 through 5 Channel until the values agree to within Conveyance 0.01 feet, or the user-defined tolerance.
1 2g
2
(α 1V 1
2 −α 2 2 + e
V ) h
Governing Equations Momentum Equation
Rapidly Varied Flow (Sharp crested weir, Hydraulic jump, Sluice gate etc)
Whenever flow encounters transition from supercritical flow to subcritical flow or viceversa, the flow varies rapidly and energy equation is not valid
Momentum equations are applied to account for various hydraulic parameters in rapidly varied flow
P2 − P1 + Wx
−
Ff = Q ⋅ ρ ⋅ ∆Vx
Governing Equations General Notes
The momentum and energy equations may be written similarly. Note that the loss term in the energy equation represents internal energy losses while the loss in the momentum equation (hm) represents losses due to external forces
In uniform flow, the internal and external losses are identical. In gradually varied flow, they are close
Basic Data Requirement Any Simulation in HEC-RAS requires following
5 steps
1)
Define geometry
2)
Define flows ( steady/unsteady analysis)
3)
Define Boundary conditions
4)
Perform Simulations
5)
Review Output and Results
All above steps are simple and user friendly in HEC-RAS provided you have sound understanding of hydraulic phenomena involve in particular analysis Before going to model practice, above mentioned five steps would be explained in next slides
Geometry Data
Geometry data Consists of following items
Reach Schematization (River layout)
Cross section data
Reach Lengths
Energy Loss Coefficients ( Friction/Expansion/Contraction)
Stream Junction information ( for two or more streams to be analyzed)
Hydraulic structure data (Bridge, Culvert, Spillway, Weir etc)
Cross-Section-Requirement
Cross section are required at representative location along a river reach where;
Slope changes
Cross section shape changes
Roughness changes
A levee starts and end
Bridge, Culverts, Weir and other control structures
Junction / Confluence
Where abrupt changes occur, several cross section should be used to describe the change regardless of the distance
Up to 500 ground points can be used to describe the cross section
HEC-RAS takes into account Cross section data with Distance taken on (xaxis)& Elevation on (Y-Axis)
Cross section should be defined perpendicular to the direction of flow (First Approximation : perpendicular to ground contour line )
Cross-Section-Layout
Cut cross section perpendicular to flow
Don’t Allow cross section to over lap while cutting
Using Standard Convention (left to right looking downstream)
Cross-Section-Layout
Understand what you are giving as input to model
The program can only reflect what is being entered
Cross-Section-Over Bank Stations
Left and right overbank stations are the locations where elevation changes abruptly. The area between these two locations represents Main Channel
Point 1 and 2 may be used as left and right overbank stations
Point 3 and 4 represents mud line and may also be used as left and right overbank stations
Cross-Section-Reach Lengths REACH LENGTHS (FLOW LENGTHS)
Measured from current cross section to the next downstream cross section
Measure reach length for left overbank
Measure reach length for Main Channel
Measure reach length for right overbank
Measure flow length relative to centroid of specified flow area
Reach length may vary from low flows to high flows
Downstream Most cross section has “ 0 ” reach length
Cross-Section-Reach Lengths
Cross-Section-Roughness
Measured from Field data
Define flow roughness for left overbank
Define flow roughness for Main Channel
Define flow roughness for right overbank
Roughness changes with water surface elevation or Discharge
HEC-RAS can model multiple Roughness
Please refer to “Hydraulic reference Manual” for representative Manning's “n” Value
Cross-Section-Roughness
Starting Water Surface Conditions Boundary condition Specification (Choose One)
Known Water surface Elevation
Compute Critical Depth
Compute Normal Depth from given Energy Grade line Slope
Interpolate Water surface Elevation from given Rating Curve
Flow Regime (Choose One)
Subcritical
Requires Downstream Boundary Condition
Supercritical
Requires Upstream Boundary Condition
Mixed Flow Regime
Require both upstream and downstream Boundary Conditions
HEC-RAS User Interface
Main Window
4 files are used to define a model 1) Project
Main File
2) Plan
Geometric “plan” layout
3) Geometry
cross section geometry data
4) Flow
Discharge boundary conditions (steady/unsteady)
HEC-RAS User Interface
Starting a new Project Do following steps …… 1) Draw a schematic river/stream diagram on Paper 2) Draw cross section locations which are available from field survey 3) Name each river cross section 4) Identify cross section location (river station) 5) In a separate excel file, note down, reach lengths, roughness values and over bank location for each cross section 6) Note down flow data to be analyzed (100-yr flood peak, 25-year inflow hydrograph, etc.) The objective of this exercise is to keep your mind clear in defining Inputs. This small effort would help in later on adjustment in Geometry data
Starting a new Project in HEC-RAS 1) Select new project from File Menu
3) Define a Project Title 4) Define Project file Name 2) Select or create the directory for project files
Starting a new Project in HEC-RAS STOP ! Before any geometry data or flow data is entered select the Unit system
Entering Geometry Data Draw the river as Schematic (from Upstream to downstream) Define Cross section
Entering Geometry Data Enter cross section data for each cross section (one by one)
20.422
S p r i n g
Cross section are ordered within Culvrt Reach a reach from the highest river station upstream to the lowest river station downstream
C r e e k
20.308
20.251 20.238 20.227
The “River Station” can have any numerical value
20.208* 20.189
20.095
The “River Station” numbering should decrease in a positive flow direction
20.000
Entering Geometry Data
Reach Lengths to next downstream cross section Manning's Roughness Values Left/Right Bank Stations (differentiates main channel) Expansion / Contraction coefficient Values Cross section Geometry
Flow Data
Run Simulation
Output Results
Cross section graphical plot
Profile Graphical plot
3D Perspective plots
Rating curve graphical plots
General variable plot profiles
General variable plot tables
Cross section Output Tables
Profile output Tables
Report Generator
Output Results Cross section graphical plot
Output Results Profile graphical plot
Output Results 3-D Perspective Graphical Plot
Output Results Rating Curve Graphical Plot
Output Results General Variable Profile Plot
Output Results General Variable Profile Table
Output Results Cross section Output Table
Output Results Profile Output Table
Output Results Report Generator
Practice Session Steady flow analysis of a Simple River Reach
Understanding Junctions
Connectivity of reach is very important as it gives information to model where to proceed in computations
Junctions are required where two or more streams come together or Split apart
Junction data editor requires Distances from Last cross section of Reach 1 to first cross section of Reach 2 and Reach 3
Understanding Junctions
Average distances should be used To minimize the errors in junction calculations, the cross section that bounds a Junction should be placed as close together as possible
Junction can be modeled using 1. Energy equation
→
Do not consider Tributary Angle
2. Momentum Equation
→
Takes into account Tributary Angle
Understanding Ineffective flow areas
Ineffective areas of cross section are the areas where water can Pond/Store. The areas from where water is not actively conveyed.
Velocity of water in these areas is minimal and may become close to zero
Understanding Ineffective flow areas
Once W.S Elevation overtops, then areas becomes effective
Do not acts like active flow area
Portion of water in this portion is included in storage calcs.
No additional wetted perimeter is added to the active flow area
Understanding Ineffective flow areas
Option-1
Define left and right ineffective flow station
Option-2
Up to 20 multiple areas can be defined at a cross section
Understanding Obstructions
The areas of cross section that are permanently blocked
Decreases flow area and add wetted perimeter along its side and top
For incorporation in Model, same options are available as that of ineffective flow area
Obstructions Examples
Understanding Levees/embankments
Levees are the earthen embankment which protects the flood plain from river floodwaters
These are defined at locations in cross sections where no water can go to the left of left levee station and to the right of right levee station until either of the levee elevation is exceeded/overtops
Limits conveyance and storage of the flood plain
Understanding Levees/embankments .035
.03
.035
60
Legend WS 06JAN2009 2400 Ground
Causes the water surface elevation to rise limits the area of flow to main river Controls flood Inundations
Levee Bank Sta 55
Left Levee
Right Levee
50 ) m ( n o i t a v e l E
45
40
35
0
5000
10000
15000
20000
25000
30000
Station (m) ) m ( n o i t a v e l E
Left Levee Overtops 45
40
35
Can be defined in cross section geometry with the same procedure as that of Obstruction
0
5000
10000
15000
20000
25000
30000
20000
25000
30000
Station (m)
50 ) m ( n o i t a v e l E
Both Levees Overtops 45
40
35
0
5000
10000
15000 Station (m)
Practice Session Ineffective flow areas, obstruction and Levee Exercise
Unsteady flow
Characterized by rate of change of flow
Represents natural flow pattern/behavior in a stream
Represents variation from low to high flow value
Unsteady flow Analysis in HEC-RAS Upstream Boundary Condition
In unsteady flow analysis, upstream boundary condition is defined as flow variation with respect to time ( flow hydrograph)
Required at upstream end of all reaches which are not connected to other reaches or storage areas Downstream Boundary Condition (same as described in steady flow analysis)
Required at downstream end of all reaches which are not connected to other reaches or storage areas
Following four types can be specified
Stage hydrograph
Flow Hydrograph
Rating Curve
Normal Depth
Unsteady flow Analysis in HEC-RAS Initial Conditions
In addition to boundary conditions, the user is required to establish the initial conditions (flow and stage) at all nodes in the river system at the beginning of the simulation.
The most common way; enter flow data for each reach, program then computes WS elevation by backwater analysis
Second way ; Use computed parameters of previous run
Define water surface elevation in any storage area connected
Unsteady Simulation-Inputs
The first step is to enter “Data time interval”
A list of available time interval would be shown in Drop Box
“Use Simulation Time” starts the hydrograph at the beginning of simulation time window
“Fixed Start Time” starts the hydrograph at user defined date and time
Inflow hydrograph Description
Inflow hydrograph Description
Abrupt changes in flow can cause instabilities--this feature assists in keeping the solution stable.
This option will monitor the inflow hydrograph to see if a change in flow rate from one time step to the next is exceeded
If exceeded, this option will automatically cut the time step in half until the change in flow rate does not exceed the specified maximum change
Unsteady Simulation- Inputs
“Min Flow” helps in stabilizing the model in low flow situations
“Min flow” allows the user to specify a minimum flow to be used in hydrograph
The “Multiplier” option allows the user to multiply every ordinate of the hydrograph by a specified factor
Performing unsteady flow Calculations
Once all the geometry and unsteady flow data have been entered, the user can begin performing the unsteady flow calculations
Select “Unsteady Flow Analysis” from the “Run” menu
Specify hydraulic table parameter (HTab Param.)
Hydraulic table parameter
Click HTab Param. Button in Geometric data Editor
Hydraulic table parameter
Where this input is used ??
Cross sections are processed into tables of elevation versus hydraulic properties of areas, conveyances and storage
Each table contains a minimum of 21 points ) a zero point at the invert and 20 computed values) and can have up to a 100 points
The interval should be specified keeping in view the full range of stages that may incurred during unsteady flow simulations
If the computed water surface goes above the table, properties are extrapolated by extending the last two points linearly. This extrapolation can often cause the model to go unstable
Performing unsteady flow Calculations
The “Geometric Processor” is used to process the geometric data into a series of hydraulic properties tables, rating curves etc.
Instead of calculating hydraulic variables for each cross section, during each iteration, the program interpolates the hydraulic variables from the tables
the processor must be run each time the geometry data is modified
Performing unsteady flow Calculations
The “Unsteady flow simulation” uses the exact same hydraulic calculations as developed for steady flow, but with a unique Skyline Matrix Solver which uses momentum equation solutions where needed
It is a three step process 1. Read user defined data 2. Convert to user defined computation interval 3. Perform simulation
The software reads the hydraulic properties table, boundary conditions and flow data from interface
Performing unsteady flow Calculations
The “Post-Processor” is used to compute detailed hydraulic information for a set of user specified time lines during the unsteady flow simulation period
If the “Post Processor” is not run, then the user will only be able to view the stage and flow hydrographs and no other output from HEC-RAS
Small computational/ output intervals would stabilize the model but consumes time for processing
Select intervals wisely, get detailed output when you really need it.
