WMS:HEC-1 Parameters

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Attributes or parameters for all HEC-1 hydrograph stations are defined and/or later edited using the Edit HEC-1 Parameters dialog. This dialog is accessed by selecting the Edit HEC-1 Parameters command from the HEC-1 menu or by double-clicking on basin, outlet, or diversion icon from the Graphics Window.

If a basin, outlet, or diversion is selected before issuing the command then data for that object appears in the text window at the bottom of the dialog. The top portion of the dialog lists the HEC-1 cards that can be edited by selecting the corresponding button. When a hydrograph station is selected (basins/outlets/diversions) only the buttons that edit parameters associated with that hydrograph station are active, all others are dimmed. In addition to using the appropriate button, HEC-1 attributes can be edited by clicking on the HEC-1 card in the text display window. Using this method, job control parameters can be edited by first toggling their display using the Display Job Control Cards toggle box, and then selecting a job control card from the text display window.

Once the dialog appears it becomes part of the main screen until you select the Done button. Therefore, you can continue to select additional, or other hydrograph stations so that data for that object may be edited without exiting the dialog. You can use the previous and next hydrograph station buttons to cycle through hydrograph stations in the order they are computed by HEC-1. Since the dialog is part of the main screen, all menu commands are active while this dialog is present.

Basin HEC-1 Cards

Precipitation...

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.

HEC-1 No Precipitation

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.

Probable Maximum Precipitation (PM)

Defining precipitation using the probable maximum precipitation option allows for the computation of the probable maximum storm according to the outdated Hydrometeorological Report No. 33 (HMR 33). This does use an outdated method and has been retained in HEC-1 for now in order to be able to reproduce results according to the old HMR 33 method.

The following variables must be defined:

• PMS – The probable maximum index precipitation from the HMR 33.
• 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.
• SWD – This value can be set to the EM 1110-2-1411 criteria or the Southwestern Division criteria.
• R6, R12, R24, R48, R72, R96 – Maximum precipitation at the specified hourly intervals as a percentage of the probable maximum storm. The R48, R72, and R96 values are optional

Unit Hydrograph Method...

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.

Snow Melt Data...

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.

Routing HEC-1 Cards

Output Control...

See Output Control... section under Basin HEC-1 Cards.

Related Topics

• Job Control Data
• Basin Data
• Loss Method
• Unit Hydrograph Method
• Precipitation
• Snowmelt
• Routing
• Reservoirs
• Diversions
• Output Control
• Model Check
• Running an HEC-1 Analysis