HEC-RAS

Evaluation of Drainage Management Software

The following sections outline the input requirements, computational methods and output options available with this software. The package was run through various tests for comparison with MTO drainage management practices provided by the MTO Drainage Management Manual (1997). A summary of out results and the requirements for using this software for MTO design, analysis or approvals is provided.The following sections outline the input requirements, computational methods and output options available with this software. The package was run through various tests for comparison with MTO drainage management practices provided by the MTO Drainage Management Manual (1997). A summary of the evaluation results and the requirements for using this software for MTO design, analysis or approvals is provided.

Model Capabilities:

Functionality:

Use in MTO Drainage Management Practices:

Summary Evaluation

Tables



Model Capabilities

What does it do?

HEC-RAS is a hydraulic modelling application developed by the US Army Corps of Engineers to simulate water surface profiles for steady and gradually varied flow in open channel watercourses. The application will estimate water surface elevation and related output along a channel reach under subcritical, supercritical ormixed flow regimes. The program is capable of modelling complicated networks with multiple reaches and tributaries. Flow through culverts, bridges, weirs and gated spillways is accommodated. Levees, blocked obstructions, lids and ineffective flow areas can also be modelled as can ice jam and debris flow conditions. The program includes an option for estimating scour at bridges for design.

With extensive input data manipulation tools and output options, HEC-RAS is an appropriate design and/or analysis tool.

Flow Definitions

Steady:
A flow condition for which the flow rate at a given point remains constant with time.
Subcritical:
A flow condition where the velocity is less than the critical velocity and the depth is greater than the critical depth.
Supercritical:
A flow condition where the velocity is less than the critical velocity and the depth is less than the critical depth.
Critical Depth:
The depth in a channel for which the specific energy is a minimum.

How does it do it?

Input data is entered through a series of input tables/windows. A watercourse is represented by a series of cross sections. Various tools are included in the program to facilitate inputting the geometric data (Geometric Data (Table 1)) including cross section interpolation, GIS/CADD file importing and graphical and tabular editors. The user then inputs design details of any structures in the watercourse (Culverts and Bridges (Table 2), Weirs (Table 3), Gated Spillways (Table 4)). The steady flow data (Steady Flow Data (Table 5)) is then entered followed by the data for at least one set of boundary condition. The program uses the standard step method to balance the energy equation or the momentum equation at each cross-section under the given flows based on the given depth of flow at the boundary cross-section. Optional computational methods are available throughout the program.

File Management

HEC-RAS includes comprehensive file management capability. A series of files are saved as a "project". A project consists of:

  • Project file (title of the project; the units system of the project; a list of all the files that are associated with the project; and a list of default variables that can be set from the interface),
  • Plan files (description and short identifier for the plan; a list of files that are associated with the plan; and a description of all the simulation options that were set for the plan),
  • Run files (the necessary data to perform the computations that are requested by the associated file plan),
  • Output files (all the computed results from the requested computational engine),
  • Geometry files ( all of the geometric data for the river system being analyzed) and
  • Steady Flow Data files (the number of profiles to be computed; flow data; and boundary conditions for each reach).

Output Options

HEC-RAS provides extensive options to view detailed information summaries and results through tables, plots, or curves. The following illustrates the available output and input options. (Select any of the hyperlinks to view a graphical representation of the information)

Figure # Tabular Output:
01 Culverts - provides detailed culvert information.
02 Bridge - provides detailed bridge information.
03 Flow Distribution - provides information of flow distribution output at any cross section.
04 Profile - displays hydraulic variables for each cross section.
  Graphical Output:
05 Cross section plots - displays X-Y perspective of a cross section.
06 Profile plots - displays variables used for computations.
07 Rating Curve - displays various graphs.
08 X-Y-Z Perspective Plot - provides a 3D view of the river system.
  Input Summary:
09 Manning's n and k values - displays Manning's n and roughness heights values for each cross section.
10 Reach Lengths - provides the cross section between reach lengths.
11 Contraction & Expansion Coefficients - provides contraction & expansion coefficients for each cross section.
12 River Stationing - displays cross section river stationing.
13 Ice Cover - displays detailed ice cover information.

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Functionality

Experience Required

A high level of understanding of open channel hydraulic processes is required for appropriate definition of input parameters, selection of calculation options and interpretation / remediation of output errors, notes and warnings.

Using the program

Use of the program itself requires basic familiarity of window based programs. The program is easy to navigate and has extensive on line help and user manuals.

Comparison to Previous Version

HEC-RAS is based on the previous hydraulic modelling application, HEC-2 developed by the US Army Corps of Engineers. Comprehensive graphical user interface functionality, improved file management capabilities and extensive output options have been added making it a much easier program to navigate and report from. As well, several changes have been incorporated in the modelling approach. These are summarized below:

Cross Section Conveyance Calculations

In both programs, cross-sections are subdivided into multiple segments and total conveyance is calculated as the sum of the conveyance in each segment. In HEC-2, the cross-sections are subdivided at each coordinate in the overbanks and the main channel is one segment. In HEC-RAS the default is to subdivide the cross-sections at each coordinate where there is a change in n-values. HEC-RAS has the option to perform calculations using the HEC-2 method.

Critical Depth Calculations

HEC-2 has only one method of calculating critical depth, which is similar to the"parabolic" method in HEC-RAS. HEC-RAS has two methods: a "parabolic" method (default) and a "secant" method. A smart feature in HEC-RAS is it automatically switches to the secant method if the parabolic method does not converge. Critical depth answers from the two programs could therefore, be significantly different. HEC-RAS, in general, will provide the more accurate answer.

Bridge Hydraulic Computations - Special Bridge Method

The HEC-2 special bridge routines use a trapezoidal approximation for low flow. The HEC-RAS program uses the actual bridge opening geometry for all of the low flow methodologies.

For low flow calculations HEC-2 combines all the pier widths and uses a single equivalent pier width placed at the centre of the trapezoid. HEC-RAS evaluates the impact of each pier individually.

HEC-2 assumes a fully submerged condition for pressure flow calculations while HEC-RAS uses the equation for fully submerged flow conditions as well as a sluice gate equation when only the upstream end of the bridge is submerged. (For further detail, please refer to C-5 of the HEC-RAS manual)

When importing a HEC-2 special bridge data into HEC-RAS, the user must input the low chord information to define the actual opening.

When defining the cross-section at a bridge, in HEC-2, the user is required to input stations that followed along the ground of the LOB, then across the bridge deck/roadway embankment; and then along the ground of the ROB. In HEC-RAS, the user only needs to define the blocked out area that is not part of the ground.

Bridge Hydraulic Computations - Normal Bridge Method

In HEC-2 pier information is either entered as part of the bridge table (BT data) or the ground information. If the user stays the energy based methods in HEC-RAS the results will be about the same. If the user wishes to use either the Momentum or Yarnell methods for low flow, they must first delete the pier information in HEC-RAS. If this is not done, HEC-RAS will not know about the pier information, and will therefore incorrectly calculate the losses with either the Momentum or Yarnell methods.

HEC-2 Normal bridge method utilizes six user input cross sections. HEC-RAS uses four user input cross sections in the vicinity of the bridge and automatically formulates 2 internal cross-section. When importing HEC-2 data, depending on how the cross sections were defined in HEC-2, HEC-RAS may end up with extra sections and thus calculate additional losses.

Stationing of the bridge table in HEC-2 had to match stations on the ground. This is not required in HEC-RAS.

Culvert Hydraulic Computations

HEC-2 can only perform culvert calculations for box and circular culvert shapes. HEC-RAS can handle the following shapes: box; circular pipe; semi-circle; arch; pip arch; vertical ellipse; horizontal ellipse; low profile arch; and high profile arch.

HEC-RAS also has the ability to mix the culvert shapes, sizes, and all other parameters at any single culvert crossing. In HEC-2 the user is limited to the same barrel shape and size.

Floodway Encroachment Computations

Floodway Encroachment capabilities in HEC-RAS were adapted from those in HEC-2. HEC-RAS, similar to HEC-2, has five optional methods for specifying flood plain encroachment. Methods 1-3 are basically the same in the 2 models. The following is a list of the differences.

HEC-RAS has an additional capability of allowing the user to specify a left and right encroachment offset.

HEC-RAS method 4 will locate the final encroachment to an accuracy of 0.01 feet, while the HEC-2 method 4 uses a parabolic interpolation method between the existing cross section points and therefore does not always find the encroachment station as accurately.

Method 5 in HEC-RAS is a combination of HEC-2's methods 5 and 6. HEC-RAS can be used to optimize for a change in water surface, a change in energy, or both parameters at the same time.

At bridges and culverts, the default in HEC-RAS is to perform the encroachment, while in HEC-2 the default is not to perform the encroachment.

At bridges where the energy based modelling approach is being used HEC-RAS will calculate the encroachment for each of the cross sections through the bridge individually. HEC-2 will take the encroachments calculated at the downstream side of the bridge and fix those encroachments stations the whole way through the bridge.

In HEC-2, if the user specifies a fixed set of encroachments on the X3 record, this would override anything on the ET record. In HEC-RAS, when the data is imported the X3 record encroachment is converted into a blocked obstruction. Therefore information on the ET record will be used in addition to the blocked obstruction.

New Computational Features in HEC-RAS

HEC-RAS can perform subcritical, supercritical, or mixed flow regime calculations all in a single execution of the program.

HEC-RAS has the ability to perform multiple bridge and/or culvert openings at the same road crossing.

At bridges, the user has the ability to use a momentum based solution for classA , B, and C low flow. In HEC-2 the momentum equation was used for class B and C flow, and requires the trapezoidal approximation. The HEC-RAS momentum solution also takes into account friction and weight forces that HEC-2 does not.

HEC-RAS can model single reaches, dentritic stream systems, or fully looped networked systems. HEC-2 can only do single reaches and a limited number of tributaries (up to three stream orders).

At stream junctions, HEC-2 has the ability to perform the calculations with either an energy based method or a momentum based method. HEC-2 only has the energy based method.

HEC-RAS has the following new cross section properties: blocked ineffective flow areas; normal ineffective flow areas can be located at any station; blocked obstructions; and specification of levees.

In HEC-RAS you can add a maximum of 500 cross sections points while in HEC-2 you had a maximum of 100 cross section points.

HEC-RAS has the ability to perform geometric cross section interpolation. HEC-2 interpolation is based on a ratio of the current cross section and a linear elevation adjustment.

HEC-RAS has an improved flow distribution calculation routine.

General Considerations

The following notes should be considered as appropriate when using this program on MTO projects or projects requiring approavl by MTO.

  • There is not always consistency between DMM and HEC-RAS variable naming conventions therefore special care should be taken in user input of coefficients etc. There is sufficient detail in the user manual to make appropriate modifications.

  • For some culverts, HECRAS will provide a headwater depth for inlet control that is lower than that produced by use of DMM nomographs. The difference increases the greater the flow but was found to be within 5% for flow rates within normal design criteria. For analysis of existing culverts that are significantly undersized, this difference may need to be considered.

  • If a culvert is flowing full HECRAS discards the inlet control solution and uses the outlet control solution as the governing energy gradeline

  • When analysing more than 13 profiles in a run, the titles on the output scramble.

  • The program can terminate successfully but not provide a valid solution. Careful attention should be given to warnings and notes.

  • The program is applicable only to scenarios of steady, gradually varied flow (except at hydraulic structures) that is one dimensional and where river channels have small slopes (less than 1:10).

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Use in MTO Drainage Management Practice

Overall, the use of this model is acceptable by MTO. The method and parameter options available throughout the program allow for compliance with the methodologies and parameters covered in the Drainage Management Manual.

Minimum Requirements for Inclusion in Report

This section provides some guidance to designers, analyst and reviewers on the type of information and minimum requirements for reporting the results of a HEC-RAS analysis. This by no means should be considered a comprehensive list of the information included in a drainage report.

Summary of input parameters:

Due to the fact that data input into HEC-RAS is done through a series of input windows, no printable input file can be provided (as is the case with HEC-2). Therefore, summary tables should be provided listing the values of the various coefficients used in the analysis and which computational methods were chosen. As well, any variance from accepted practise should be explained.

When reviewing a report that includes a HEC-RAS analysis, careful attention should be given to the review of input parameters. In HEC-RAS, the user can set all parameters. However, some parameters are given default values (Parameters with Program Default Values (Table 6)). Parameters that have been left at their default values should be noted and an assessment made to whether this is appropriate. Refer to the DMM for values applicable to Ontario where available. The HEC-RAS manual also provides guidelines.

As well as input parameters, HEC-RAS provides various computational method options. Note which computational methods have been left at their default (Computational Methods (Table 7)) and assess whether this is appropriate. Refer to the DMM for methods applicable to Ontario where available. The HEC-RAS manual also provides guidelines.

Tabular and Graphical Output

The report should include both tabular and graphical output showing the water surface profile for the different flow rates assessed (2-100 year) in both "profile" and "cross-sections" views, at a minimum. HEC-RAS provides extensive output options therefore any recommendations from the analysis should be supported by including additional relevant output.

The output should have logical consistency between cross-sections and whether the watercourse has been adequately represented.

The user/reviewer should ensure that a HEC-RAS analysis is valid. The program is applicable only to scenarios of steady, gradually varied flow (except at hydraulic structures) that is one dimensional and where river channels have small slopes (less than 1:10).

Summary of Calculation Tolerances

HEC_RAS relies on tolerance values to determine convergence of the numerical analysis. These values can be set by the user with a preset range. The accuracy of the results will depend on the tolerance values entered. Therefore the table summarizing calculation tolerances should be provided.

HEC-RAS defaults to a set of calculation tolerances (Calculation Tolerances (Table 8)) that will allow the program to converge on a solution in a reasonable time based on the recommended hardware. If the user has changed the default tolerances, the rationale should be provided for this change.

Summary of errors, warnings and notes

The model can provide an extensive array of messages to notify the user to pay attention to specific results. The messages can be either error messages, warnings, or notes.

Error messages (Sample Error Messages (Table 11)) will only occur when the program cannot complete a run. Generally this is due to missing data. If the program did not crash, you can view the error in the summary of Errors, Warnings, and Notes. If the program crashed, you can view a log file that will give you a detailed computational summary of the steps before it crashed. A completed analysis should not include error messages.

A summary of errors, warnings and notes associated with each scenario analyzed should be provided. If some warnings could not be resolved a justification of why the analysis is acceptable must be included. This should include an assessment of such warnings on the results of the analysis.

A warning message (Common Warning Messages (Table 9)) will occur when steady flow computations have been completed and the program has detected problems that may or may not require the user's attention. For example:

The program will often assume critical depth or minimum error depth when the energy equation cannot be determined. These are not valid solutions and the effect on the overall profile should be assessed.

Warning messages may also indicate the geometric data does not adequately represent the watercourse. Messages related to large changes in conveyance, velocity or energy might indicate that more cross sections are needed to accurately estimate energy losses between sections.

Therefore when reviewing the HEC-RAS output careful attention should be given to warnings. The program may "terminate successfully" and compile all output but not provide a valid solution. Note messages (Common Note Messages (Table 10)) inform the user about how the program is performing the computations. The notes should be reviewed to assess whether the way the program is performing the computations is as intended and is an accurate representation of the scenario being modelled.

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Summary Evaluation

Go to the HTML version of the Summary Evaluation of HEC-RAS, or download the PDF version (39 KB)

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Tables

Input Parameters - Geometric Data (Table 1)

Parameter Purpose
Cross-section station & elevation Defines channel shape
Reach lengths (left,right,channel) Defines path of watercourse
Manning's n values Used for friction loss calculations
Expansion / Contraction coefficients Used for expansion or contraction loss calculations
Ineffective Flow areas Defines the flow area
Levees Defines the flow area
Blocked obstructions Defines the flow area
Thickness of ice Used for ice jam calculations
Manning's n for ice Used for ice jam calculations
Ice cover specific gravity Used for ice jam calculations
Internal friction angle of jam Used for ice jam calculations
Coefficient K1 Used for ice jam calculations
Ice jam porosity Used for ice jam calculations
Max mean velocity under ice Used for ice jam calculations

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Input Parameters - Culverts and Bridges (Table 2)

Parameter Purpose
Bridge Data (and Culvert Deck)
Station ,high & low cord elevations Defines bridge opening and weir flow
width
Distance to upstream station Locates bridge/culvert on watercourse
Centreline elevation and station of piers Defines bridge opening
Skew angle of piers Defines bridge opening
Station & elevation of abutments Defines bridge opening
Skew angle of abutments Defines bridge opening
Upstream / Downstream embankment slopes Defines bridge opening
Weir coefficient (for deck) For overtopping calculation
Max submergence Used for conveyance calculations
Minimum weir flow elevation For overtopping calculation
Pressure Flow Cd :
  • submerged inlet
  • Inlet&outlet submerged
  • Max low cord
Used for conveyance calculations
Coefficient of Drag Used for conveyance calculations
Pier Shape K Used for conveyance calculations
Weir Crest Shape Used for conveyance calculations
Culvert Data
Shape Defines culvert
Diameter (or rise & span ) Defines culvert
Length Defines culvert
Chart # Refers to Federal Highway Admin. HDS 5 (1985)
Scale # Refers to Federal Highway Admin. HDS 5 (1985)
Entrance loss coefficient Used to calculate headloss for outlet control
Exit loss coefficient Used to calculate headloss for outlet control
Culvert 'n' value Used to calculate headloss for outlet control
Centreline stations Locates culvert on watercourse
# of Barrels For total conveyance
Upstream & Downstream invert Used to calculate slope

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Input Parameters - Inline Weir (Table 3)

Parameter Purpose
Distance to upstream station Locates inline weir on watercourse
Station , elevation Defines weir geometry
Upstream & downstream embankment sideslope Defines weir geometry
width Defines weir geometry
Weir Coefficient Used for conveyance calculations
Weir Crest Shape Used for conveyance calculations

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Input Parameters - Inline Gated Spillway (Table 4)

Parameter Purpose
Height Defines gated spillway geometry
width Defines gated spillway geometry
Invert and centreline stations Defines gated spillway geometry
Discharge coefficient Defines gated spillway geometry
Gate Type Used for conveyance calculations
Trunnion Exponent Used for conveyance calculations
Opening Exponent Used for conveyance calculations
Head Exponent Used for conveyance calculations
Orifice Coefficient Used for conveyance calculations
Trunnion Height Used for conveyance calculations
Weir Coefficient Used for conveyance calculations
Weir Crest Shape Used for conveyance calculations

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Steady Flow Data (Table 5)

Parameter Purpose
Steady flow rate(s) analized Sets flow rates to be analyzed
Starting water surface elevation Boundary condition to start calculations from
Flow regime Determines bakcwater or frontwater calculations, or both

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Input Parameters with Program Default Values (Table 6)

Parameter Default Value
Geometric Data
Cross-section station & elevation May use interpolation tool
Reach lengths (left,right,channel) No default
Manning's n values No default
Expansion / Contraction coefficients Expansion = 0.1
Contraction = 0.3
Ineffective Flow areas At left and right overbanks
Levees At left and right overbanks
Blocked obstructions At left and right overbanks
Thickness of ice No default
Manning's n for ice No default
Ice cover specific gravity 0.916
Internal friction angle of jam 45 degrees
Coefficient K1 0.33
Ice jam porosity 0
Max mean velocity under ice 1.524 m/s
Bridge Data (and Culvert Deck)
Station ,high & low cord elevations No default
width No default
Distance to upstream station No default
Centreline elevation and station of piers No default
Skew angle of piers No default
Station & elevation of abutments No default
Skew angle of abutments No default
Upstream / Downstream embankment slopes 0
Weir coefficient (for deck) 1.44
Max submergence 0.95
Minimum weir flow elevation Lowest upstream highcord
Pressure Flow Cd :
  • submerged inlet
  • Inlet&outlet submerged
  • Max low cord
0.8
Coefficient of Drag No default
Pier Shape K No default
Weir Crest Shape Broadcrested
Culvert Data
Shape Circular
Diameter (or rise & span ) No default
Length No default
Chart # 1 - Concrete Pipe Culvert
Scale # 1 - Square edge entrance with headwall
Entrance loss coefficient No default
Exit loss coefficient 1.0
Culvert 'n' value No default
Centreline stations No default
# of Barrels No default
Upstream & Downstream invert No default
Inline weir data
Distance to upstream station No default
Station , elevation No default
Upstream & downstream embankment sideslope 0
width No default
Weir Coefficient 1.66
Weir Crest Shape Braodcrested
Inline gated spillway data
Height No default
width No default
Invert and centreline stations No default
Discharge coefficient No default
Gate Type Sluice (Radial)
Trunnion Exponent 0 (0.16)
Opening Exponent 1 (0.72)
Head Exponent 0.5 (0.62)
Orifice Coefficient 0.8
Trunnion Height No default
Weir Coefficient 3
Weir Crest Shape Broadcrested

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Default Computational Methods (Table 7)

Computational Method Default
Bridge Calculation Options
Add friction and or weight component to momentum equation Add friction component
Set default location for critical depth during class B flow Inside bridge at upstream end
Set Criteria for computing pressure flow Upstream energy gradeline
Properties of ice jam through bridge No ice jam computed
Approach for low flow calculations Energy equation
Approach for high flow calculations Energy equation
Floating debris none
Culvert Calculation Options
Solution criteria Highest upstream energy gradeline
Junction Options  
Computation mode Energy equation
Steady Flow Calculation Options
Method for calculating average conveyance At break in n values
Method for calculating friction slope Average conveyance
Method for calculating critical depth Parabolic method

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Default Calculation Tolerances (Table 8)

Factor Tolerance
Water surface calculation tolerance .003
Critical depth calculation tolerance .003
Maximum # of iterations 20
Maximum difference tolerance .1
Flow Tolerance factor .001

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Common Warning Messages (Table 9)

Warning Message Explanation
The velocity head has changed by more than 0.5 ft (0.15m). This may indicated the need for additional cross sections. Implies there has been a significant change in the average velocity between this section and the section immediately downstream. This could reflect a significant change in slope or a dramatic change in cross-section shape. The user needs to assess whether the loss is appropriate. More sections may be supplied to allow the program to more accurately calculate energy losses

The energy loss was greater than 1.0 ft (0.3m) between the current and previous cross section. As a default, the program uses an average conveyance equation to determine energy loss. Actual rate of energy loss is usually not linear. Therefore if the cross sections are too far apart, an appropriate energy loss will not be determined. This warning is to flag a large energy loss and the user needs to assess whether the loss is appropriate. More cross sections or an alternate method to compute average friction slope may be warranted. May also indicate a misrepresentation of the effective flow area of the cross-section.

The energy equation could not be balanced within the specified number of iterations. The program used critical depth for the water surface and continued on with the calculations. During the computation of upstream water surface elevation the program could not compute energy losses to provide a flow depth in the specified flow regime. This may be due to poor cross section data, cross sections to far apart, wrong flow regime specified or the program is having trouble balancing a water surface elevation very close to the top of a levee or ineffective flow area.

During standard step iterations, when the assumed water surface was set equal to critical depth, the calculated water surface came back below critical depth. This indicates that there is not a valid subcritical answer. The program defaulted to critical depth.

This warning may be associated with too long of reach lengths between cross-sections or the fact that the flow analysis should be performed in the supercritical or mixed flow regime.
Divided flow computed for this cross-section

Flow is occurring at more than one portion o the cross section. User must verify if this is possible.
The conveyance ratio (upstream conveyance divided by downstream conveyance) is less than 0.7 or greater than 1.4. This may indicate the need for additional cross sections.

Implies that the cross-sectional areas are change in dramatically between the two cross sections and additional cross sections may be added to more accurately calculate expansion and contraction losses.
The parabolic search method failed to converge on critical depth. The program will try the cross section slice/secant method to find critical depth The parabolic search method is the default method to calculate critical depth. If this method fails the program will automatically try the secant method and provide this warning. The user should examine closer the critical depth that was determined to ensure that the program supplied a valid answer

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Common Note Messages (Table 10)

Note Message Explanation
Hydraulic Jump has occurred between this cross section and the previous upstream section.

Provides the location of a Hydraulic jump
Program found supercritical flow starting at this cross section.

Provides the location of supercritical flow
The energy method has computed a class B profile. Whenever Class B low flow is found to occur the modeller should perform the analysis in the mixed flow regime.

The downstream water surface is below the minimum elevation for pressure flow. The sluice gate equations were used for pressure flow. The sluice gate equation was used because the water surface elevation at the river station immediately below the bridge was less than the lowest value of the low cord for the bridge.

The downstream water surface is above the minimum elevation for pressure flow. The orifice equations were used for pressure flow. The orifice equation was used because the water surface elevation at the river station immediately below the bridge was higher than the lowest value of the low cord for the bridge.

For the cross section inside the bridge at the upstream end, the water surface and energy have been projected from the upstream cross sections. The selected bridge modeling method does not compute answers inside the bridge.

For the cross sections inside the bridge at the downstream end, the water surface is based on critical depth over the weir. The energy has been projected.

Multiple critical depths were fond at this location. The critical depth with the lowest, valid, energy was used. When the secant method is used to determine critical depth, this note will appear if more than one minimum energy point is found. This may occur for cross sections with large, flat overbanks. The user should examine closer the critical depth that was determined to ensure that the program supplied a valid answer.

The momentum method has computed a class B profile. Whenever Class B low flow is found to occur (ie a hydraulic jump is assumed to have occurred) the modeller should perform the analysis in the mixed flow regime.

The culvert inlet is submerged and the culvert flows full over part or all of its length. Therefore, the culvert inlet equations are not valid and the supercritical result has been discarded. The outlet answer will be used

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Sample Error Messages (Table 11)

Errors Message Explanation
Error - Incomplete data, the following errors were found:
River: "Mimico Creek" Reach: "Tributary"
RS:7.0
- no Station Elevation Data.

Station Elevation Data is missing.
Error - Incomplete data, the following errors were found:
River: "Mimico Creek" Reach: "Tributary"
RS:7.0
- Main channel length not set.

Main channel length of cross section is incomplete.
Error - Incomplete data, the following errors were found:
River: "Mimico Creek" Reach: "Tributary"
RS:6.97
- Deck station data is not in increasing order on upstream side, stationing needs to maintain (vertical walls) or increase.

Deck station numbers are missing
Error - Incomplete data, the following errors were found:
River: "Mimico Creek" Reach: "Tributary"
RS:7.0
- No Manning's n data or friction height k set.

Manning's n data for a cross section is missing.
Error - Incomplete data, the following errors were found:
River: "Mimico Creek" Reach: "Tributary"
RS:6.97
- Culvert: Culvert #1 rise not set.
- Culvert: Culvert #1 Length not set.
- Culvert: Culvert #1 Distance from upstream cross section to culvert inlet not set.
- Culvert: Culvert #1 Manning's n value not set.
- Culvert: Culvert #1 entrance loss coefficient not set.
- Culvert: Culvert #1 exit loss coefficient not set.
- Culvert: Culvert #1 upstream invert elevation not set.
- Culvert: Culvert #1 downstream invert elevation not set.
- Culvert: Culvert #1 centreline stations not set so #Barrels = 0.

Culvert Data is incomplete.

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