Welcome to CivilGEO Knowledge Base
Welcome to CivilGEO Knowledge Base
Welcome to CivilGEO Knowledge Base
Welcome to CivilGEO Knowledge Base
The Green and Ampt infiltration method is essentially a simplification of comprehensive Richard’s equation for unsteady water flow in soil. This method should only be used for event simulation and not for a continuous simulation where there is an extended dry period(s) between precipitation events. It assumes the soil is initially at uniform moisture content, and infiltration occurs with so-called piston displacement. It is also assumed that the soil layer is infinitely deep, so reaching saturation can be defined purely by the Green and Ampt equation. The method automatically accounts for ponding at the soil-air interface.
In GeoHECHMS, the Compute Green Ampt command is used to compute the Green and Ampt infiltration parameters for each subbasin based upon the hydrologic soil data.
Follow the steps below to use the Compute Green Ampt command:
The following sections describe how to use the Compute Green Ampt command and interact with the above dialog box.
The Select Subbasins section includes a table that lists all the subbasins contained within the current scenario along with their initial content, saturated content, initial deficit, suction head, and hydraulic conductivity.
This section is used to manually select subbasins from the Map View. If a subbasin is already selected on the Map View before running this command, the same subbasin will be shown selected within the table.
Alternatively, click the [Pick] button to interactively select subbasins from the Map View. On clicking the [Pick] button, the Compute Green Ampt dialog box will temporarily disappear. A prompt will be displayed on the status bar instructing the user to select subbasins from the Map View. After selecting the subbasins, the user can press the [Enter] key or right-click and choose Done from the displayed context menu. The dialog box will be redisplayed, and the total number of selected subbasins will be displayed in the Total selected read-only entry.
Note that the user can select multiple subbasins from the Map View before running the Compute Green Ampt command by holding the [Ctrl] key while selecting the desired subbasins.
The Define Computational Data section contains a Soil moisture method dropdown option and three panels that are the GIS Polygon Layer, the NRCS Layer, and the Default Values. From these three panels, the user can compute Green Ampt infiltration parameters for the various methods available.
This dropdown combo box allows the user to select a method for specifying the initial soil moisture state. Two available options are:
Based on the option selected, the content of the GIS Polygon Layer and the Default Values panels will be enabled and disabled.
This panel is used for the user-defined soil map polygon data. The soil map data provides hydrologic soil group data for each defined polygon.
The following entries are provided in the data panel:
The NRCS Layer panel uses data from the NRCS Soil Survey Database to determine the hydrologic soil group data for the watershed region. This web soil survey database is only available within the USA and does not work outside the USA.
Note that for countries other than the USA, the software provides similar soil survey databases. This data panel will change to represent the one that is available for the project area. The software will automatically download the data once the user has selected this option and the command is executed.
Under the NRCS Layer panel, the two available subpanels are mentioned below.
This subpanel allows the user to define the setup to be used in computing the Green Ampt parameters using the NRCS soil survey database.
Initial soil moisture content estimate
This radio button selection allows the user to specify the initial soil moisture conditions at the beginning of the simulation in terms of volume ratio. The following options are provided:
This subpanel is used to see the parameters that were computed from the NRCS soil textures that were determined from the soil classifications.
This panel is used to define the default values for computing the Green Ampt infiltration parameters.
The following input parameters are provided in the data panel:
When the data has been defined in the Compute Green and Ampt dialog box, click the [Compute] button.
The software will then look at each subbasin selected and compute the Green Ampt infiltration parameters for each subbasin. The computed values will be shown in the Select subbasins editable column as shown below. The software also allows the user to modify these computed values.
Note that while the computation is running, the [Close] button changes to [Cancel] so that the user can abort applying the computed Green Ampt parameters values if desired..
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