Visual OTTHYMO v2.0

Evaluation of Drainage Management Software

The following sections outline the input requirements, computational methods, and output options available with this software. The theoretical basis of this software was compared with the MTO Drainage Management Manual (1997). A summary of model capabilities, and the requirements for using this software for MTO design, analysis, or approvals is provided.

General Information

Model Capabilities:

Functionality:

Use in MTO Drainage Management Practices:

Information Sources:
VO2 User Guide
VO2 Reference Manual
INTERHYMO/OTTHYHO 89 Manual
www.grnland.com*
www.schaeffers.com*


General Information

Title of Software: Visual OTTHYMO
Purpose: Single Event Hydrologic Modelling
Publisher: Greenland International Consulting Inc. / Schaeffer & Associates Ltd.
Version: 2.0
Year Published: 2001
Platform(s): Win95, Win98, Win2000, WinME, WinNT
System Requirements: Required: Pentium 233 MHZ, 32 MB of RAM (64 MB or higher preferred), 4 MB Video Card Memory, 100 MB of hard disk spaceRecommended: Educational/Professional Version- 64 MB of RAM, 8 MB video memory, Pentium 400. Enterprise Version- 128 MB of RAM, 16 MB video memory, Pentium 850.
Availability: www.schaeffers.com/VO2/buy.shtml

Note: For a complete list of upgrades/changes refer to software documentation available from Scheaffer Engineering.

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Model Capabilities

What does it do?

Visual OTTHYMO version 2.0 (VO2) is a single event hydrologic model used to simulate hydrographs by modelling rainfall, infiltration, runoff and routing through a watershed.

The program requires the user to develop the watershed by placing an assortment of hydrologic "objects" on a project "canvas" thereby creating a visual representation of the system.

When each hydrologic object is selected the user inputs various parameters, as required, to define the objects site specific variables. The simulation is then run for the desired design storm. Model output is available in text and graphical formats.

The model is an appropriate design tool for use in projects such as watershed studies and stormwater management design.

How does it do it?

As described, the building blocks of the VO2 program are hydrologic objects selected by the user to represent the study watershed. These objects are divided into four colour coded categories and grouped in the program's toolbox in the following categories: Watershed Commands, Routing Commands, Operational Commands, and Utility Commands.

  1. Watershed Commands (Generate Hydrograph Objects)

    There are four unit hydrograph options available, depending on the characteristics of the area being modelled. Each hydrograph object represents a catchment in the model area. A detailed summary of input parameters can be found at the bottom of this document.

    STANDHYD - Uses parallel instantaneous unit hydrographs for impervious and pervious areas of the catchment. Infiltration is calculated using one of several methods, Horton's infiltration equation, the SCS modified CN method, or the proportional loss method. This method is recommended for modelling urban watersheds with greater than 20% impervious areas.

    NASHYD - Uses the Nash instantaneous unit hydrograph method. The hydrograph is calculated based on a series of N reservoirs. Infiltration is calculated using the SCS modified CN method, or the proportional loss method. The Nash method is recommended for rural areas but can also be applied to large urban areas and to simulate infiltration in a stormsewer.

    WILHYD - Uses the Williams and Hann (HYMO) unit hydrograph method. Infiltration is calculated using the SCS modified CN method. This method is recommended for rural watersheds with long recession periods.

    SCSHYD - Uses the Nash hydrograph method based on SCS parameters and with N= five reservoirs. Similar to NASHYD it is recommended for rural areas

  2. Routing Commands

    Channel routing calculations are used to estimate the transformation of a streamflow hydrograph as a storm event moves through the drainage system. There are 4 hydrologic routing methods available in VO2, and all are based on the continuity equation and a storage discharge relation.

    ROUTE CHANNEL - Uses the variable storage coefficient method to calculate channel storage based on average channel characteristics and travel time based on Manning's equation. The channel cross section geometry is defined by a series of up to 20 X and Y coordinates entered by the user. The channel width can be divided into up to 6 segments with varying Manning's n values.

    ROUTE PIPE - Applies variable storage coefficient method to circular and rectangular pipes. Allows only one value of Mannings n. The pipe dimension is automatically re-sized if the values entered are not sufficient to pass the peak flow.

    ROUTE MUSKCUNG - Applies the Muskingum-Cunge channel routing method. The channel cross section geometry is defined by a series of up to 20 X and Y coordinates entered by the user. The channel width can be divided into up to 6 segments with varying Manning's n values. The user is also required to enter a constant, Beta, for the stage-discharge curve determined by the channel geometry.

    ROUTE RESERVOIR - Reservoir routing routine applies the storage-indication method to solve the continuity equation to determine reservoir outflow. The storage discharge relation for the reservoir is required.

  3. Operational Commands (Modify Hydrograph Objects)

    ADD HYD - Adds two hydrographs.

    SHIFT HYD - Translation of the hydrograph by a specified time step.

    DIVERT HYD - Splits a single hydrograph into up to 5 hydrographs.

    DUHYD - Used to separate major and minor hydrographs from a total hydrograph.

  4. Utility Commands (Manual Input Hydrograph Objects)

    READ HYD - Reads a saved hydrograph file.

    STORE HYD - Allows the user to enter the ordinates of a known hydrograph.

Rainfall/Storm Information

Rainfall data is entered through the raingaugue form. The model can handle up to 4 raingaugues, each with up to 10 storm simulations. The user specifies which hydrograph each rainguage pertains to.

There are three model storms available, they are: Chicago Storm, Mass Storm, and Read Storm. Data for the Mass Storm and Read Storm options are read into the model from a properly formatted external text file. The Chicago storm distribution is calculated from user entered values for the time to peak ratio and either the regression constants A, B and C, or time/intensity pairs.

The program also allows the variation of the design storm to account for aerial reduction and movement of the storm system through the watershed.

File Management

In Visual OTTHYMO 2.0 a collection of files is saved as a "project" in a master file with a *.vop extension. A project is launched by opening the main project file.

Some of the files that may be included in a project are:

  • Scenario file (*.sce, contains input data for each object in the model)
  • Connectivity file (*.mdr, information to run the model)
  • Database file (vo.mdb, contains output information)
  • Detailed Output file (*.out, the detailed output file in ASCII)
  • Summary Output file (**.sum, the summary output file in ASCII)
  • Storm file (*.stm, ASCII file hyetograph input into model)
  • Mass Storm file (*.mst, ASCII file mass curve input into model)
  • Hydrograph file (*.hyd, ASCII file hydrograph input into model)

There are two options for saving files:

  • Save Project (saves all scenarios in a project)
  • Save Scenario (saves only the current scenario)

Individual scenarios can be closed independent of the project, allowing the user to have only the scenario(s) of interest running.

Output Options

There are five options available for output generation:

  • Summary Data - output from selected locations within the model.
  • Hydrograph Data - Table of hydrograph points
  • Hydrograph Plot - Hydrograph Plot - plot of hydrologic data
  • Detailed Output File - detailed text file containing all output data for each object
  • Summary Output File - summary text file containing key output data for each object.

The users guide recommends that the project schematic be exported to a 3rd party word processing software to be printed.

There is no option to print input parameters separately from output files.

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Functionality

Experience Required

The visual nature of the model makes the program quite user friendly, as the watershed is built on the screen using the various icons provided. Anyone familiar with using the Microsoft toolbox/toolbar format will be comfortable with the layout of the program interface.

The program has a user manual and reference guide included on the CD and help is available from Schaeffer Engineering by email or telephone.

As with all models a sound understanding of the hydrologic processes to be modelled is required for appropriate selection of input parameters and computational methods. Application of any hydrologic model to highway drainage design should only be undertaken with sound engineering judgement and a thorough understanding of the models application and limitations.

Using the program

OTTHYMO is supplied on a CD-ROM, and the program installs automatically. A pass code is required to activate the program. This must be obtained from Schaeffer Engineering by emailing vo2@shaeffer.com with the system I.D. number, and program serial number. Use of the program requires basic familiarity with Windows based programs.

Data requirements are similar to that required for hand calculation.

A comprehensive Users Guide and Reference Manual are included on the CD. The Users Guide contains directions on creating and manipulating models and is easy to follow. The Reference Manual contains the background theory and a detailed breakdown of each hydrologic object. The Manual also contains various tips, including some guidance on the selection of computational methods and parameters.

Error and warning messages appear on the model screen and in the output files. The Users guide contains a listing of the common error and warning messages for reference.

A program help file is included in the software. This file can be searched via an index or through the help search menu for key words or topics. Additionally, help on specific areas of the program is available by pressing F1 while in the relevant dialogue box without having to go through the help menu.

The program also contains three example models which illustrate how VO2 can be applied to specific situations (new sub-watershed model, importing a model from OTTHYMO-89, sizing a stormwater pond).

Comparison to Previous Version

Visual OTTHYMO 2.0 is the latest of many enhancements to the original HYMO model created by Williams and Hahn (U.S. Dept. of Ag.) in 1973. HYMO (1973) was initially developed for rural watersheds. Other previous versions have been: OTTHYMO-83, INTERHYMO/OTTHYMO-89, and Visual OTTHYMO (v1.0 and v1.05).

Visual OTTHYMO v2.0 was released in 2001, the program provides a number of enhancements over previous versions:

  • A new graphical user interface
  • A new interface layout and object organization
  • The ability to import background images
  • Improved model output files
  • The option to run only certain portions of the model

VO2 is backward compatible with Visual OTTHYMO v 1.0, OTTHYMO-89/INTERHYMO, and OTTHYMO-83, although some modification of older files may be required.

There were no changes in hydrologic theory associated with the upgrade to VO2.

A summary of changes to the program can be found below in table 1.

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Use in MTO Drainage Management Practice

The use of this model is acceptable on MTO projects. The methods applied by the program generally comply with those contained in the MTO Drainage Management Manual. Previous versions of OTTHYMO are also accepted with the exception of OTTHYMO V1.0.

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 CulvertMaster analysis. This by no means should be considered a comprehensive list of the information included in a drainage report.

Summary of input parameters

VO2 does not facilitate printing of input parameters, however input data is included in the Detailed Output file. Other information provided in a report should include:

  • Supporting information regarding watershed discritization.
  • Sufficient background information regarding the study area to support parameter choice.
  • Rationale behind selection of storm type/settings.
  • Selection criteria for unit hydrograph.
  • The model schematic.
  • Calibration and verification process and description of data used.

Tabular and Graphical Output

The report should include:

  • The detailed output file. This includes:
    • Storm input data (see input data tables 6 and 7 below for complete list of parameters).
    • Storm hyetograph data table generated by the model.
    • Description of unit hydrographs (e.g. Area, % impervious, % pervious, IA, TP. Manning's, slope, etc. For a complete list of parameters see input data tables 2 and 3 below).
    • Any transformed hyetograph data tables generated.
    • The results of all hydrograph operations (add hyd, shift hyd, divert hyd, du hyd) i.e. Q peak, T peak, area totals.
    • The final results for the outflow in question, i.e. Q peak, T peak.
  • Hydrograph plots at key locations for pre and post development conditions.
  • A summary table of peak flow rates at all key locations for pre and post development conditions.
  • In the case of using the model for SWM detention/retention design, the volume, dimensions, and corresponding water level for the design flow rates and level of control.
  • Discussion and justification of any unresolved warning or error messages.
  • Any other output pertinent to the model should also be included, for example the results of any calibration studies and intermediate results as required to justify/support conclusions.

Recommended Review Steps

The following steps are recommended for review of OTTHYMO results:

  • Review calibration and verification process and adequacy of data used.
  • Review model schematics, including background information such as aerial photographs and topographic and other maps. Determine if discritiziation is adequate and correct.
  • Review input information in terms of object and parameter selection (e.g. selection of IUH, routing commands).
  • Review design storm selection.
  • Review output paying special attention to notes and error/warning messages.
  • Review hydrograph plots at key locations.

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Tables

Summary of changes from INTERHYMO/OTTHYMO 89 to Visual OTTHYMO 2.0 (Table 1)

Item/Command Visual OTTHYMO 2.0 INTERHYMO/OTTHYMO 89
Interface
  • Graphical user interface.
  • Improved interface layout.
  • Background Images can be imported.
  • Improved output files.
Input files are text files created externally in ASCII format.
Simulation Options Portions of the model can be run independently.
Objects Hydrologic objects are grouped and colour coded for easy identification. All data entry through code (text files), no graphical object representation.
Rain Rainfall data can be entered directly in the hydrograph object. Not an option.
Hydrographs Four Hydrograph options:
  • Stanhyd
  • Nashyd
  • Scshyd
  • Wilhyd
No change in IUH's available. The user can adjust all parameters on all hydrograph objects.
Equipped with separate objects called "DESIGN" or "CALIB" (e.g. CALIB STANHYD). CALIB allows user to enter all parameters, DESIGN allows limited user input. In total 6 Hydrograph options:
  • Design Stanhyd
  • Design Nashyd
  • Design Scshyd
  • Calib Stanhyd
  • Calib Nashyn
  • Calib Wilhyd
COMPUTE VOLUME Option removed from program. Approximates the storage volume required to reduce the inflow peak to a known release rate.
COMPUTE RATING CURVE Option removed from program. Computes the stage-area-flow relationship for a channel section using Manning's equation.
EXTRAN Option removed from program. Program included the option to format files appropriately for export into Extran 89.

Note: For a complete list of upgrades/changes refer to software documentation available from Scheaffer Engineering.

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Input Parameters - Watershed Commands (Table 2)

Parameter Description
STANHYD
NHYD Object number between 1 and 9999.
DT Simulation time step (min).
AREA Watershed area, ha.
XIMP Ratio of directly connected impervious areas, between 0 and 1.
TIMP Ratio of total impervious area, must be greater than or equal to XIMP.
DWF Base flow, m3/s
LOSS Determines the loss method to be applied.
1=Horton's equation,
2=SCS modified CN,
3=Proportional Loss method.
SLPP Slope of pervious area, %.
LGP Length of overland flow path pervious area, m.
MNP Manning's n for pervious surface.
SCP Storage coefficient for the linear reservoir of the pervious areas, hr.
DPSI Depression storage for impervious area, mm.
SLPI Slope of impervious area, %.
LGI Length of overland flow path impervious area, m.
LGI=1 manually input
LGI=2 calculated by A=1.5*L^2
MNI Manning's n for impervious surface.
SCI Storage coefficient for the linear reservoir of the impervious areas, hr.
RAIN Option for user to enter rainfall data directly into hydrograph, mm/hr at DT intervals.
LABEL Option to add a label to the hydrologic object.
 
NASHYD
NHYD Object number between 1 and 9999.
DT Simulation time step (min).
AREA Watershed area, ha.
DWF Base flow, m3/s
CN SCS curve number or Proportional loss coefficient (if -ve).
IA Initial abstraction, mm. If IA<0 program uses SCS method to calculate losses.
N Number of linear reservoirs.
TP Time to peak, hr.
RAIN Option for user to enter rainfall data directly into hydrograph, mm/hr at DT intervals.
LABEL Option to add a label to the hydrologic object.
 
WILLHYD
NHYD Object number between 1 and 9999.
DT Simulation time step (min).
AREA Watershed area, ha.
AA/DWF Base flow, m3/s
BB Printing option.
0=print rainfall excess ordinates,
1=do not print same.
CN Curve number.
IA Initial abstraction, mm.
K Recession constant, hr.
TP Time to peak, hr.
RAIN Option for user to enter rainfall data directly into hydrograph, mm/hr at DT intervals.
LABEL Option to add a label to the hydrologic object.
 
SCSHYD
NHYD Object number between 1 and 9999.
DT Simulation time step (min).
AREA Watershed area, ha.
DWF Base flow, m3/s.
CN Curve number.
TP Time to peak, hr.
RAIN Option for user to enter rainfall data directly into hydrograph, mm/hr at DT intervals.
LABEL Option to add a label to the hydrologic object.

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Input Parameters - Infiltration Loss Methods for STANHYD (Table 3)

Parameter Description
Horton's Method
Fo Initial infiltration rate, mm/hr.
Fc Final infiltration rate, mm/hr
DCAY Decay constant, /hr.
F Moisture in soil at beginning of storm, mm.
DPSP Depression storage for pervious area, mm.
 
SCS Modified CN Method
CN Curve number.
IA Initial Abstraction, mm.
 
Proportional Loss Coefficient Method
C Proportional Los Coefficient ratio, 0-1.
IA Initial Abstraction, mm.

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Input Parameters - Routing Commands (Table 4)

Parameter Description
ROUTE CHANNEL
NHYD Object number between 1 and 9999.
DT Time step, min.
CHLGTH Length of channel, m.
CHSLOPE Channel slope, %.
FPSLOPE Flood plain slope, %.
VSN Valley section number, a reference number between 1 and 9999.
NSEG Number of segments in channel cross section, max 6.
ROUGH, SEGDIST Roughness over the segment width, m
DIST, ELEV Channel cross section shape co-ordinates.
LABEL Option to add a label to the hydrologic object.
 
ROUTE MUSKCUNG
NHYD Object number between 1 and 9999.
DT Time step, min.
CHLGTH Length of channel, m.
CHSLOPE Channel slope, %.
FPSLOPE Flood plain slope, %.
VSN Valley section number, 1 to 9999.
BETA Constant for stage-discharge curve. Between 1 and 1.67.
NSEG Number of segments in channel cross section, max 6.
ROUGH, SEGDIST Roughness over the segment width, m
DIST, ELEV Channel cross section shape co-ordinates.
LABEL Option to add a label to the hydrologic object.
 
ROUTE PIPE
ITYPE Pipe shape.
1=circular,
2=rectangular
DIAM Diameter of circular pipe, mm.
Width, Height Dimensions of rectangular pipe, mm.
NHYD Object number between 1 and 9999.
PIPE Pipe number between 1 and 9999.
PLNGTH Pipe length, m.
ROUGH Manning's n.
SLOPE Slope of pipe, m/m.
DT Time step, min.
LABEL Option to add a label to the hydrologic object.
 
ROUTE RESERVOIR
NHYD Object number between 1 and 9999.
DT Time step, min.
RATING CURVE Allows input discharge-storage curve.
DISCHARGE, STORAGE Pairs of values to describe discharge-storage relationship, m3/s & ha/m.
LABEL Option to add a label to the hydrologic object.

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Input parameters - Operational Commands (Table 5)

Parameter Description
ADD HYD
NHYD Object number between 1 and 9999.
LABEL Option to add a label to the hydrologic object.
 
SHIFT HYD
NHYD Object number between 1 and 9999.
TLAG Lag time for the hydrograph, min.
LABEL Option to add a label to the hydrologic object.
 
DIVERT HYD
NHYD Object number between 1 and 9999.
FLOW table Specify flow split between up to 5 hydrographs.
NHYD1…NHYD5 Object number for outlet hydrographs no. 1-5.
Q1(n)..Q5(n) Hydrograph outflow when the inflow is QTOTAL(n), m3/s. n=1-20.
LABEL Option to add a label to the hydrologic object.
 
DUHYD
NHYD Object number between 1 and 9999.
CINLET Peak flow capture rate, m3/s.
NINLET Number of inlets in the drainage system with capture rate of CINLET.
FLOW table Connection to downstream NHYD's.
MAJID NHYD of major system connection.
MINID NHYD of minor system connection.
LABEL Option to add a label to the hydrologic object.
 
READ HYD
NHYD Object number between 1 and 9999.
FILEPN Filepath of hydrograph.
LABEL Option to add a label to the hydrologic object.
 
STORE HYD
NHYD Object number between 1 and 9999.
DT Time step, min.
AREA Watershed area, ha.
HYD POINTS Hydrograph ordinates, m3/s. Up to 2000 pairs.
LABEL Option to add a label to the hydrologic object.

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Input Parameters - Assign Rain Gauge (Table 6)

Parameter Description
Chicago Storm
IUNITS SI or metric.
TD Duration of storm, hr.
R Ratio of time to peak to total duration.
SDT Storm's time increment, min.
ICASE Method for IDF curve calculation.
1=Regression Equation (User specifies constants A,B&C),
2=Manually entered Time/Intensity Pairs.
 
Mass Storm
PTOT Total precipitation, mm.
SDT Storm's time increment, min.
CRV Name Mass curve file path.
 
Read Storm
STMFNAME Storm file path.

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Input Parameters - Modify Storm (Table 7)

Parameter Description
Modify Storm 1=R Fact Factor
NSHIFT Time step.
RFACT Factor to adjust rainfall increments.
 
Modify Storm 2=R Fact=XK*XL**XM
NSHIFT Time step.
XK Constant.
XL Distance from the epicentre of storm to centre of watershed, km.
XM Exponent used in equation.

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