WMS:Basin HEC-1 Cards

Edit HEC-1 Parameters dialog

When a basin is selected in the HEC-1 model, selecting HEC-1 | Edit Parameters will bring up the Edit HEC-1 Parameters dialog with the Basin HEC-1 Cards section active. The following can then be specified:

HEC-1 Basin Data Dialog

Dialog is accessed by selecting HEC-1 | Edit Parameters... in WMS and then choosing Basin Data... from the Edit HEC-1 Parameters dialog.

Basin name– Each hydrograph station should be identified with a unique name. This name appears as part of the KK record for that station in the input file.

Area – Areas should be entered in either square miles or square kilometers.

Basin Descriptor (Optional) – Option for more Description of the Basin.

Input hydrograph (QI, BI) –

• Direct input hydrograph (QI) – This hydrograph can be input by selecting the checkbox.
• Define QI – Allows for the definition of the direct input hydrograph. Click to open the XY Series Editor dialog.
• Tape 21 input hydrograph (BI) – Select to indicate that the data should be input as a general hydrograph.
• Tape 22 input hydrograph (BI) – Select to indicate that the data should be input as a specific hydrograph.

Observed hydrograph (QO) –

• Define QO – Allows the definition of the outflow hydrograph. Click to open the XY Series Editor dialog.

Base Flow Parameters – Base flow parameters can be defined for a basin by selecting the Enter base flow checkbox. The input parameters for base flow are as follows:

• Enter base flow – Select this to enter the defined base flow.
• STRTQ – Flow at the start of the storm in cfs (cms for metric units).
• QRCSN – Flow in cfs (cms) below which base flow recession occurs in accordance with the recession constant RTIOR. In other words, it is that flow where the straight line (in semilog paper) recession deviates from the falling limb of the hydrograph.
• RTIOR – The ratio of the recession flow (QRCSN) to that flow occurring one hour later (Must be greater than or equal to 1).

HEC-1 Output Control Dialog

HEC-1 Output Control dialog

Dialog is accessed by selecting HEC-1 | Edit Parameters... in WMS and then choosing Output Control... from the Edit HEC-1 Parameters dialog.

Comment Lines section – Individual comments can be defined for each hydrograph station. These comments can be used to identify unique characteristics about a particular basin or outlet point.

• New – Select to add a new comment.
• Delete – Select to delete an existing comment.

Output Control (KO) – These controls determine what information about a given hydrograph station is written to the HEC-1 ASCII output file.

• Print Control (field 1) – controls how the data collected is printed.
  • "Use IO record (O)" – Default setting, prints the entire IO record.
  • "Print all output (1,2)" – When selected, prints all output.
  • "Print input and summaries" – When selected, it will just print input and summaries of the data.
  • "Print input data only (4)" – When selected, it will print the input data only.
• Plot Control (field 2) – Section where plots can be controlled.
  • "Use IO record (O)" – Plots are dependant on the IO record.
  • "No printer plots (1)" – Select if there are no printer plots.
  • "Plot hydrograph (2)" – Select to receive output on the plot hydrograph.
• Plotting Scale (field 3) – Section to specify the plotting scale.
• Unit 7 Control (field 4) – If the unit 7 control should be on select yes, if not select no.
• Hydrograph Control (field 5) – Section designated to control the output of hydrographs.
  • "TAPE22 file (22)" – The file read by WMS for the display of hydrographs. This should only be changed to suppress particular hydrographs.
  • "TAPE 21 file (21)" – The file used to suppress particular hydrographs.

For each hydrograph station (basin hydrographs, combined hydrographs, and routed hydrographs) different output controls can be specified. This dialog is accessed by selecting the Output Control dialog button from the Edit HEC-1 Parameters dialog. Entries which can be defined in this dialog are described below.

Routed and Combined Hydrographs at Outlets

In WMS an outlet point is used to represent locations where hydrographs are both combined and then routed. Therefore, if an outlet is selected before choosing the Output Control dialog, a radio group at the top of the dialog appears to specify whether the options should be applied to the combined or routed hydrograph. If a basin is selected the radio group at the top of the dialog does not appear.

HEC-1 Precipitation Dialog

HEC-1 Precipitation dialog

Precipitation patterns are assigned to basins by first selecting the appropriate basin(s) and then clicking on the Precipitation button in the Edit HEC-1 Parameters dialog. If multiple basins are selected then the defined parameters will apply to all selected basins.

NOTE: If no basins are selected, the parameters can be applied to all basins.

Dialog is accessed by selecting HEC-1|Edit Parameters... in WMS and then choosing Precipitation... from the Edit HEC-1 Parameters dialog.

If no precipitation for a given basin is chosen, then the program will use the precipitation pattern of the most recently defined basin. In other words, if the same precipitation pattern is to be used for each basin, specify precipitation at the upper-most basin and let all other basins "inherit" this same pattern.

No Precipitation – Select if there was no precipitation. Basin average (PB) – Select to specify the Basin Average.

• Average precipitation: – Enter the average precipitation in inches here.
• Define Series – Select to bring up the XY Series Editor dialog.
• Get Precip From Web – Select to bring up the Get Online NOAA Atlas 14 Data dialog.

Gage (PG) – Gages can be used with or without a terrain model. If drainage basins have been defined using a TIN, the appropriate gage weights (using the Thiessen polygon method) for each basin are automatically computed when the Compute (or Update) Basin Data command is executed.

• PT Gage Weights – Section where gage weights can be changed/assigned.
• PR Gage Weights – Section where gage weights can be changed/assigned.

Hypothetical storm (PH) – Select to define the characteristics of a hypothetical storm.

• Define Storm – Select to bring up the XY Series Editor dialog.
• Frequency – Enter the frequency of a hypothetical storm here.
• Storm area: – Enter the area of the hypothetical storm in mi^2.

Probable Maximum Precipitation (PM) – Allows for the computation of the probable maximum storm according to the outdated Hydrometeorological Report No. 33 (HMR 33).

• PMS: – Enter the probable maximum index precipitation from the HMR 33. Recorded in inches.
  • % of PMS – Click to bring up the HEC-1 Percentage of PMS dialog.
    • Maximum 6-hour percentage of PMS – Maximum amount of probable precipitation inside a 6 hour time period.
    • Maximum 12-hour percentage of PMS – Maximum amount of probable precipitation inside a 12 hour time period.
    • Maximum 24-hour percentage of PMS – Maximum amount of probable precipitation inside a 24 hour time period.
    • Maximum 48-hour percentage of PMS – Maximum amount of probable precipitation inside a 48 hour time period.
    • Maximum 72-hour percentage of PMS – Maximum amount of probable precipitation inside a 72 hour time period.
    • Maximum 96-hour percentage of PMS – Maximum amount of probable precipitation inside a 96 hour time period.
  • SWD – Click to open the Precipitation Distribution dialog.
    • EM 1110-2-21411 criteria – Represents the standard flood determinations for the project.
    • Southwestern Division criteria – Represents the flood determinations for the southwestern division.
• TRSPC: – Precipitation adjustment (between 0 and 1.0) based on drainage area size. If this value is set at zero HEC-1 will default it to the appropriate value based on the HOP Brook Adjustment Factor as described in the HEC-1 manual.
• TRSDA: – The drainage area in square miles for which the storm is transposed.

Loss Method...

HEC-1 Loss Method dialog

One of several different loss methods can be chosen when generating synthetic hydrographs. A loss method is assigned to a basin by first selecting the basin and then choosing the Loss Method button in the Edit HEC-1 Parameters dialog. As with other basin data the same parameters can be assigned to several basins by selecting multiple basins before accessing the Loss Method dialog.

When defining a kinematic wave model, it may be necessary to define a separate set of loss parameters for the two different UK records (generally corresponding to pervious and impervious area). This second set of loss parameters is defined from within the Unit Hydrograph Method dialog.

Uniform Loss Method (LU)

This loss method uses an initial value and a uniform value to define infiltration losses. Input parameters are as follows:

• STRTL – Initial rainfall/snow melt loss in inches (mm) for snow free ground.
• CNSTL – Uniform rainfall/ loss in inches/hour (mm/hour) which is used after the starting loss (STRTL) has been satisfied.
• RTIMP – Ratio of drainage basin that is impervious. Values should be less than or equal to 1.

Losses (LM)

Losses are used in conjunction with the uniform (LU) or exponential (LE) loss methods. The parameter descriptions are as follows:

• STRKS – The starting value of the loss coefficient on the exponential recession curve for losses in in/hour (mm/hour) when used with the exponential loss rate (LE) or the uniform melt water loss rate (in/hour) when used with the uniform loss rate (LU).
• RTIOK – Rate of change of the loss-rate parameter computed as the ratio of STRKS to a value of STRKS after ten inches of accumulated loss when used with the exponential loss rate or not used when using the uniform loss rate.

Exponential Loss (LE)

Parameters for the exponential loss method are as follows:

• STRKR – The starting value of the loss coefficient on the exponential recession curve for rain losses.
• DLTKR – The amount in inches (mm) of initial accumulated rain loss during which the loss coefficient is increased.
• RTIOL – Parameter computed as the ratio of STRKR to a value of STRKR after ten inches (ten mm) of accumulated loss.
• ERAIN – Exponent of precipitation for rain loss function that reflects the influence of the precipitation rate on basin-average loss characteristics.
• RTIMP – Ratio of drainage basin that is impervious. Values should be less than or equal to 1.

Green & Ampt (LG)

Green-Ampt infiltration loss parameters are as follows:

• IA – Initial loss (abstraction) in inches (mm).
• DTHETA – Volumetric moisture deficit. If this value is 0, then the method reduces to the initial loss equal to IA and a constant loss equal to XKSAT.
• PSIF – Wetting front suction in inches (mm). If this value is 0, then the method reduces to the initial loss equal to IA and a constant loss equal to XKSAT.
• XKSAT – Hydraulic conductivity at natural saturation in inches/hour (mm/hour).
• RTIMP – Ratio of drainage basin that is impervious. Values should be less than or equal to 1.

Using methods defined by the Maricopa County Flood Control District, Green-Ampt parameters can be determined from GIS data layers automatically in WMS.

Holtan (LH)

Parameters used to define the Holtan loss method:

• FC – Holtan's long term equilibrium loss rate in inches/hour (mm/hour) for rainfall/losses on snow free ground.
• GIA – Infiltration rate in inches/hour per inch *BEXP (mm/hour per mm *BEXP) of available soil moisture storage capacity.
• SAI – Initial depth in inches (mm) of pore space in the surface layer of the soil which is available for storage of infiltrated water.
• BEXP – Exponent of available soil moisture storage.
• RTIMP – Ratio of drainage basin that is impervious. Values should be less than or equal to 1.

SCS Loss Method (LS)

The SCS curve number method uses the following parameters:

• STRTL – Initial rainfall abstraction in inches (mm) for snowfree ground. If value is 0, then initial abstraction will be computed as:

$0.2*{\frac {(1000-10*CRVNBR)}{CRVNBR}}$.

• CRVNBR – SCS curve number for rainfall/ losses on snowfree ground.

NOTE: Composite Curve Numbers can be computed automatically when this method for computing losses is chosen and a terrain model is present.

• RTIMP – Ratio of drainage basin that is impervious. Values should be less than or equal to 1.

Unit Hydrograph Method...

HEC-1 Unit Hydrograph Methods dialog

One of several different unit hydrograph methods can be chosen when generating synthetic hydrographs. A method is assigned to a basin by first selecting the basin and then choosing the Unit Hydrograph Method button from the Edit HEC-1 Parameters dialog. As with other basin options the same parameters can be assigned to several basins by selecting multiple basins before accessing the Unit Hydrograph Method dialog.

Clark Unit Hydrograph (UC)

The parameters for the Clark method are as follows:

• T_C – Time of concentration in hours for the unit hydrograph. Several different equations exist for determining the time of concentration. The list of basin geometric attributes computed automatically when basins have been delineated from a terrain model can be useful in many of these equations. These attributes can be viewed from within the Unit Hydrograph Method dialog by choosing the View Basin Geometrical Attributes button. Time of concentration can be computed from one of several equations using these attributes, or by using a time computation coverage. These options are accessed from the Compute Parameters – Basin Data and Compute Parameters – Map Data buttons respectively.
• R – The Clark storage coefficient in hours.
• TIME AREA CURVE – The time area curve defines the area of the watershed contributing runoff to the basin outlet as a function of time. This curve is defined by selecting the check box and then activating the XY Series Editor with the adjacent button. The time area curve can be computed automatically from a TIN (this method will not work for watersheds delineated from DEMs or Feature Objects) using the Compute Time Area Curves button.

Snyder (US)

Parameters for the Snyder unit hydrograph are as follows:

• TP – Lag time in hours. Several different equations have been published to determine the lag time of a basin. Many of these use some of the geometric attributes computed automatically when a terrain model is present. These attributes can be viewed by choosing the View Basin Geometrical Attributes button. Lag time can be computed from one of several equations using these attributes, or by using a time computation coverage. These options are accessed from the Compute Parameters – Basin Data and Compute Parameters – Map Data buttons respectively (see Computing Travel Times).
• CP – Peaking coefficient.
• TIME AREA CURVE – The time area curve defines the area of the watershed contributing runoff to the basin outlet as a function of time. This curve is defined by selecting the check box and then activating the XY Series Editor with the adjacent button. The time area curve can be computed automatically from a TIN (this method will not work for watersheds delineated from DEMs or Feature Objects) using the Compute Time Area Curves button.

SCS Unit Hydrograph (UD)

Parameters for generating a unit hydrograph using the SCS dimensionless method include:

• TLAG – SCS lag time in hours. Several different equations have been published to determine the lag time of a basin. Many of these use some of the geometric attributes computed automatically when a TIN is present. Lag time can be computed from one of several equations using these attributes, or by using a time computation coverage. These options are accessed from the Compute Parameters – Basin Data and Compute Parameters – Map Data buttons respectively.

Kinematic Wave (UK)

Distributed outflow from a basin may be obtained by utilizing combinations of three conceptual elements: overland flow planes, collector channels, and a main channel. These elements can be defined if the kinematic wave option is specified.

The first and second kinematic wave records can be used to distinguish between different properties such as pervious/impervious (grass/pavement). For each record, the following parameters can be supplied.

• L – Overland flow length.
• S – Representative slope.
• N – Manning's roughness coefficient.
• A – Percentage of sub-basins area that this record represents (The total of the two records must sum to 100).
• Losses – A loss method must be defined for each plane. Choosing the Define Loss button will present the Standard Loss Method dialog and allow a method to be chosen and parameters defined.

In addition to the kinematic wave records, collector channels and a main channel must be defined. Either kinematic wave (RK) or Muskingum-Cunge (RD) routing can be specified by selecting the appropriate radio button. A dialog for defining the channels is accessed by choosing the Define Channels button. The main channel must be defined, whereas the two collector channels are optional. The following parameters are used for each channel:

• L – Channel length.
• S – Channel slope.
• N – Manning's roughness coefficient for the channel.
• CA – Contributing area to the channel.
• SHAPE – The characteristic shape of the channel.
• WD – Channel bottom width or diameter.
• Z – Side slopes if the channel type requires it.

For the main channel, only an eight point cross section as defined with the RC, RX, RY cards can be used.

A flag for routing upstream hydrographs can be specified for the main channel from within this dialog as well.

Derived Unit Hydrograph (UI)

A given unit hydrograph determined from a separate analysis can be input using the XY Series Editor. The given unit hydrograph must be derived for the same time interval as is specified on the IT record in the Job Control dialog.

Snow Melt Data...

HEC-1 Snow Melt Data dialog

When snow needs to be considered in the runoff analysis, snow melt data for a basin needs to be defined. HEC-1 has two different methods for computing snowfall/melt simulations: the Degree-Day method, and the Energy-Budget.

To define data for a selected basin, choose the Snow Melt Data button from the Edit HEC-1 Parameters dialog. The toggle at the top of the dialog turns snow calculations on. For both methods the elevation or zone data, the coefficients, and temperature data must be defined.

The Degree-Day method is set up once these parameters have been defined. If the Energy-Budget method is toggled on then the Dew point, Short-wave radiation, and Wind speed data must be defined as well. Losses should be defined when either method is used. These losses are used in conjunction with the LU or LE cards for normal basin losses. The check box at the bottom of the dialog allows losses to be turned on or off for a given simulation.

Elevation Zone Data (MA)

Snow computations are accomplished in HEC-1 using separate, equally incremented, elevation zones within each basin. The number of elevation zones for which data must be defined is determined by specifying the base elevation of zone 1 and zone interval in the appropriate edit fields. The default values correspond to the lowest elevation and the range between the highest and lowest elevation (i.e. one elevation zone). More zones can be created by decreasing the interval, or lower elevations can be excluded from calculations by increasing the base elevation. Once the base elevation and interval are set, elevation zone data is defined by choosing the Define MA Data button. The number of zones which need to be defined is automatically determined and the appropriate edit fields are unhighlighted. The elevation zone parameters are as follows:

• AREA – The drainage area associated with this elevation zone.
• SNOPACK – The snow pack depth.
• AVEPRECIP – The normal annual precipitation in inches (mm) for this zone.

Areas for the elevation zones can be computed and supplied automatically using the Compute Areas button. The elevation fields are not part of the HEC-1 input.

Radiation

These three data records (dew point, radiation and wind speed) are only defined for the Energy-Budget method. Like the temperature time series, these three HEC-1 records are defined using the XY Series Editor. Dates for IN records can be specified using the appropriate edit fields and the beginning time and time increment are defined using the XY Options dialog from within the XY Series Editor.

Temperature (MT)

The temperature time series is entered using the XY Series Editor where each value corresponds to the air temperature at the bottom of the lowest elevation zone for that interval. The starting date is determined from the IN record values in the edit fields corresponding to the temperature data. The starting time and time increment (also part of an IN record) are specified in the XY Series Editor using the XY Options dialog.

Related Topics

• HEC-1 Parameters
• Computing Composite CN
• Computing Travel Times
• Computing the Area Between Contours
• XY Series Editor
• Obtaining Precipitation Data