QHM - continuous watershed modeling - storm management system - stormwater runoff - dendritic systems
QHM Categories: hydrological database/modeling/data analysis, surface-water models, water quality, watershed modeling
QHM Detailed Description
QHM is capable of continuous simulation of:
QHM simulation can represent a period of indefinite length (limited only by available disk space). The model can be used on a discrete event or multi-event continuous basis.
Constituents that can be simulated are: stormwater runoff (flow rate and volume) and, optionally, one or any combination of: one pollutant exhibiting first-order decay or characteristics simulated using a rating curve; sediments (in up to five size fractions) characterized by discrete particle settling; and instream erosion indices based on cumulative excess boundary shear stress.
Appropriate flow and pollutant records obtained elsewhere (monitoring or other simulation models) can be routed through ponds or river reaches by the model.
QHM System Components
Components of a physical system that can be simulated are:
A system comprised of any combination and any number of the above components can be simulated provided that each component of the system and the system as a whole can be described as "one-way" or "non-feedback."
Looping networks, or ponds where outflow depends on water depth in the receiving channel, are examples of situations which might not be well-represented in this model. A typical application appropriate for QHM would be a dendritic river network with channels adequately represented by uniform flow conditions.
When the QHM program opens, the user can select from seven options of which four represent standard Windows utilities. The other three are specific to QHM: HELP, RUN, and UTILITY; these are introduced here and explained in more detail below.
The HELP menu includes, in addition to Windows Help, the complete contents of the user's manual.
The RUN menu includes three commands:
UTILITY also includes three commands:
The DEFAULT button will display settings that many users prefer.
The QHM program is structured as a series of commands which are summarized in the PROGRAMS COMMAND section herein and described in detail in the user's manual.
This section summarizes information that a user must have at hand before using QHM. Appendix A of the user's manual includes three step-by-step exercises that will guide a first-time user through the basic operation of QHM.
Defining the Problem
It is assumed that the user has identified the problem that the simulation will address:
QHM Input Data
Further details about input data requirements and file formats are provided in the INPUT DATA section of the user's manual. Required data includes:
Input file formats must be standard formats that are recognized by QHM and must be identified during program setup.
In the input file, the user will specify the nature and form of outputs required after a simulation run: each output file is identified in terms of a Series and ID number. The program, in UTILITY/SET RUN OPTIONS, will ask the user to select the name and extension for the output file and to select output options.
QHM ID and Series Numbers
An ID number is used by QHM to identify a file that contains a time series of flow data that is generated by the program. ID numbers are assigned by the user to identify a flow series at the outlet of a sub-watershed, watershed, pond, reservoir, or channel. Because output quality data, if generated, will be contained in the same file as the flow data, they will also be identified by the same ID number.
The maximum number of flow series files that is retained by the program is 24. If a simulation run creates more than 24 flow series, the user must decide which of the previously created files will be overwritten in order to reassign the ID number to another series; the data in the overwritten files will be lost. In many cases this will not matter, e.g., after flows simulated for two sub-watersheds are combined, the individual files may not be of interest.
If the user wants to retain a record of a flow series before an ID number is reassigned, that series can be recorded by the PRINT SERIES, DUMP PRINT, or DUMP PLOT commands.
In addition to an ID number, each outflow series is also assigned a Series Number. Series Numbers are not recognized by the program; they are intended to allow the user to keep track of files when many files are generated by a single simulation run.
If a simulation run does not generate more than 24 flow series, they will all be identified by their ID numbers; in this case Series Numbers, although they must be entered, will be redundant, and dummy values can be used.
QHM Time Steps
Input data time steps may be 5, 10, 15, 20, 30 or 60 minutes, or 24 hours, for precipitation; monthly for evaporation; or hourly or daily for flow.
The program can be instructed to perform calculations based on any specified time step. If the calculation time step is less than the precipitation time step, the program will use the average precipitation value in each calculation time step. If the calculation time step exceeds the precipitation time step, the latter will be used as the calculation time step.
Time steps for input precipitation data are specified in the START command. Calculation time steps are specified in the GENERATE command. If a flow series not generated by the program is to be provided using the STORE command, the data input time step will be identified under that command. The routing time step for the POND, RESERVOIR, and REACH commands is specified in those commands.
Table 1 lists sample input files that are included with the program, sample data files that are recognized by each input file and indicates the program command that the input file is intended to illustrate. It also indicates the data format of each sample data file.
TABLE 2 - QHM SAMPLE DATA FILES
Convert Data Format
Create Graph File
If the start and end dates are not specified, the complete file will be plotted. If more than one file is plotted and the time periods of the files to be plotted are not the same, the program will plot the portion of the selected time period that is common to all of the files.
Set Run Options
The initial screen first allows the user to choose whether the File Setup screen will be displayed here ("No"), or will be displayed when a simulation run is commenced under RUN ("Yes").
Particularly for long simulation runs, the user may wish to follow the progress of the run by a display of the QHM command that is currently being executed. If this choice is selected, the display options allowed by the next set of choices will not be available.
The "Display Output" menu allows a choice of "Utility Commands" which places the output from selected commands identified in the input file in text files which are displayed in the editor at the end of the run.
The save button will save the preceding instructions. If the answer to the initial question was "No," a File Setup screen will appear. Here the user must enter the names of Primary Input and Output files and applicable data files to be used in subsequent simulation runs.
The settings in the Set Run Options screen, once saved, will be retained until this screen is reopened, i.e., if repeated simulations are run using the run command, the same run options will apply for each run.
If the File Setup screen was previously created, the simulation run will begin when "Run QHM" is selected.
This command will allow a graph created under UTILITY/CREATE GRAPH FILE to be retrieved, viewed, and printed. The following are steps required to plot a graph using the QHM graph program:
The user must begin by opening an input (.inp) file. If an existing file is selected, it will be overwritten.
The Input Interface cannot be used to edit an existing input file; this can be done in a text editor. Note also that once information from an Input Interface screen is written to file it cannot be corrected in this utility; corrections must be made using a text editor. (An option to use of this interface is to edit sample files provided with the program to represent the user's system.)
The Input Interface menu is organized in terms of groups of QHM commands as follows:
The user is expected to invoke these commands in the order in which they will appear or reappear in the input file. The following deals briefly with individual commands which are discussed in detail in the user's manual.
If POLLUTANT RATES is selected, coefficients must be entered, where applicable, for impervious and pervious surfaces and base flow. If SEDIMENT SIMULATION is selected, soil settling velocities and size factors must be provided. In either case, buildup and washoff calculation methods, coefficients, and exponents must be identified.
The QHM program is structured as a series of separate commands. These can be invoked as necessary, in any order after the START command, to simulate a particular physical system. The following paragraphs provide a brief overview of these commands and describe the required format for command lines and input data. Chapter 3 of the user's manual provides detailed information about each of these QHM commands.
QHM commands can be grouped into these three categories.
QHM Control Function Commands
These commands (START, FINISH) allow the user to control the simulation run (i.e., initialize the run and terminate it respectively). The START command also allows the user to elect to simulate one, both, or neither of the pollutant types in the model.
These commands also define the type of algorithm that the model will use for pollutant simulation and provide parameters necessary for these algorithms. Subject to certain restrictions noted below, the START command can be issued repeatedly through a run as required to modify generation methods, parameters, or simulation spans.
QHM Hydrologic Simulation Commands
These are the actual functional commands of the model and represent the entire repertory of simulation capability. The commands allow the user to carry out the following operations:
QHM Output and Utility Commands
These commands include:
QHM Data Formats
Format of Command Lines
COMMAND NAME ((text) (parameter)) ((text) (parameter))...
The sequence of commands is entirely up to the user except that the first command must always be a START, and the last command must always be a FINISH.
Any line beginning with an asterisk is treated as a comment and is not interpreted by the model. A comment line cannot occur within a command line series. It must occur between command lines. Any non-comment line with an asterisk in column 80 causes a page feed to be generated after the line is read but before it is echoed.
Format of Rainfall Lines
A) AES Format:
B) HEC "STORM" Format:
Rainfall data must be supplied if the GENERATE command is used but is otherwise not required. Rainfall lines must be supplied for days where rain occurs but may be supplied for all days during a simulation span including dry days. Note that the time step (DTINC) in the GENERATE Command must be equal to or less than the precipitation time step.
As noted below, the file number for rainfall data to be used in the simulation is specified in the START command (typically described as device 9). GENERATE commands only read rainfall data specified in the most recent START command. The reissue of a START command during a run therefore allows the user to change rainfall records applied in the simulation.
Format of Temperature Lines
A) AES Format:
B) HEC "STORM" Format:
The GENERATE command looks for the temperature data on device 8. Hourly temperature must be supplied if snowmelt is requested. Otherwise temperature data may be omitted.
To save file space, temperature data is only read from November 1st to May 31st inclusive. The temperature file must correspond to this interval with no records occurring in the interval from June 1st to October 31st inclusive.
Format of Flow Lines
A) USGS Flow Records
The number of decimal places for the streamflow values is variable depending on the magnitude of the streamflow. The field is always eight columns wide. The value is given to two decimal places for flow less than 1 CFS, one decimal place for flow of 1 CFS or greater but less than 10 CFS, and no decimal places for flow of 10 CFS or greater. There is a decimal point only if there are decimal places. The field for a nonexistent day, for example, November 31 or September 31, is blank.
B) WSC Hourly Flow Records
Eight leading blank or character spaces followed by three two-byte ASCII integer values (year, month, day), and two blank or character spaces followed by six ten-byte ASCII values of hourly flow rates in cubic feet per second or cubic meters per second. Format: (8A1,3I2,2X,6F10.3)
C) WSC Daily Flow Records
line 1: Nine leading blank or character spaces followed by two two-byte ASCII integer values (year and month) and a blank or character space and ten five-byte ASCII values separated by a space or character value describing flow rate in either cubic feet or cubic meters per second, then four blank or character spaces and one two-byte ASCII integer value for the number of days per month (NDYMO). Format: (9X,2I2,1X,10(I5,1X),4X,I2)
line 2: The format is as described above except that the last variable, number of days per month (NDYMO), is excluded. Format: (9X,2I2,1X,10(I5,1X))
line 3: The format is as specified for line 2 except that eleven flow values are read rather than ten if NDYMO=31. Otherwise line 2 is repeated. Format: (9X,2I2,1X,11(I5,1X))
Flow data must be supplied if the STORE command is used but is otherwise not required. Flow lines must be supplied for all days during the time span indicated by the user on the STORE command.
As noted below, the FORTRAN file number for flow data to be input is specified in the START command (typically assign to device 10). The STORE commands only read flow data specified in the most recently preceding START command. The reissue of a START command during a run therefore allows the user to change flow records stored by the model.
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