Hec Ras Training Day 1

HEC-RAS Training Course

Aug-2009University of Engineering

and TechnologyLahore

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.

RELEVANCE POINT

Authorizations

• Relevance Point is an authorized reseller for Mathworks, AutoDesk, Sperian, Boss 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 LicensesUniversity of Engineering & Technology, Lahore.01 LicenseMehran University of Engineering & Technology, Jamshoro. 01 LicenseNED 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, 2009UET-Lahore on August 28-29, 2009

Training CourseWater Surface Profile Modeling Using

HEC-RAS

HEC-RAS Training Course

Aug-2009University of Engineering

and TechnologyLahore

Training ObjectivesUnderstand 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 ContentsDAY-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 / DiscussionsModeling a tributary /Junctions

Understanding of Ineffective flow areas / Levees

Understanding of flow Obstruction

Unsteady Flow Analysis of a simple river reach

Practice session / Discussions

Course ContentsDAY-2

Modeling a Bridge

Modeling a Culvert

Modeling Multiple Openings

Practice session / DiscussionsModeling 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 HistoryDeveloped 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 1995Version 2.0 released in July 1997Version 2.2 released in July 1999Version 3.0 released in January 2001Version 3.1 released in January 2003Version 3.1.1 released in May 2003

Version 3.1.3 released in May 2005

Common Practical ProblemsHow 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 Capabilities1-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 EquationsEnergy Equation

Gradually Varied FlowComputations 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 Procedure1. 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.

5. Compare the computed value of WS2 with value assumed in step 1; repeat steps 1 through 5 until the values agree to within 0.01 feet, or the user-defined tolerance.

ehVVg

WSWS +−+= )(21 2

2221112 αα

Channel Conveyance

Rapidly Varied Flow (Sharp crested weir, Hydraulic jump, Sluice gate etc)

Whenever flow encounters transition from supercritical flow to subcritical flow or vice-versa, the flow varies rapidly and energy equation is not valid

Momentum equations are applied to account for various hydraulic parameters in rapidly varied flow

xfx12 VρQFWPP ∆⋅⋅=−+−

Governing EquationsMomentum Equation

The momentum and energy equations may be written similarly. Notethat 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

Governing EquationsGeneral Notes

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-RequirementCross 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 (x-axis)& 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-LayoutUnderstand 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 ChannelPoint 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 LengthsREACH 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-RoughnessMeasured from Field data

Define flow roughness for left overbank

Define flow roughnessfor Main Channel

Define flow roughnessfor 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 ConditionsBoundary 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 ProjectDo 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-RAS1) Select new project from File Menu

2) Select or create the directory for project files

3) Define a Project Title

4) Define Project file Name

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

Culvrt Reach

20.422

20.308

20.25120.238

20.227

20.208*

20.189

20.095

20.000

Spr

i ng C

re ek


Enter cross section data for each cross section (one by one)

Cross section are ordered within a reach from the highest river station upstream to the lowest river station downstream

The “River Station” can have any numerical value

The “River Station” numbering should decrease in a positive flow direction


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 ResultsCross 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 ResultsCross section graphical plot

Output ResultsProfile graphical plot

Output Results3-D Perspective Graphical Plot

Output ResultsRating Curve Graphical Plot

Output ResultsGeneral Variable Profile Plot

Output ResultsGeneral Variable Profile Table

Output ResultsCross section Output Table

Output ResultsProfile Output Table

Output ResultsReport Generator

Practice SessionSteady flow analysis of a Simple River Reach

Understanding JunctionsConnectivity 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 JunctionsAverage 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 canPond/Store. The areas from where water is not actively conveyed.

Velocity of water in these areas is minimal and may become close to zero


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


Option-1 Define left and right ineffective flow station

Option-2 Up to 20 multiple areas can be defined at a cross section

Understanding ObstructionsThe 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/embankmentsLevees 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/embankmentsCauses the water surface elevation to rise

limits the area of flow to main river

Controls flood Inundations

Can be defined in cross section geometry with the same procedure as that of Obstruction

0 5000 10000 15000 20000 25000 3000035

40

45

50

55

60

Station (m)

Ele

vatio

n (m

)

Legend

WS 06JAN2009 2400

Ground

Levee

Bank Sta

.035 .03 .035

0 5000 10000 15000 20000 25000 3000035

40

45

Station (m)

Ele

vatio

n (m

)

0 5000 10000 15000 20000 25000 3000035

40

45

50

Station (m)

Ele

vatio

n (m

)

Left Levee Right Levee

Left Levee Overtops

Both Levees Overtops

Practice SessionIneffective flow areas, obstruction and Levee

Exercise

Unsteady flowCharacterized 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-RASUpstream 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-InputsThe 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 DescriptionAbrupt 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 timestep 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


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


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


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.

Practice SessionUnsteady flow analysis of a Simple River Reach

Documents

Hec Ras Training Day 1