Rainfall Distribution

Rainfall distribution refers to the pattern or distribution of rainfall over a specified location for a given time period. It helps to understand how precipitation is distributed among cities or regions over a certain period. Different regions of the Earth’s surface receive an uneven distribution of rainfall each year and at different times. Meteorological conditions, geographical location, closeness to water bodies, topographical features, etc., are some of the factors that influence the uneven distribution of rainfall.

The CivilGEO software supports rainfall distributions to define precipitation data. The user can browse the location of interest by selecting the country and then the local region and the software will provide the rainfall distribution for the specified storm frequency. In addition, the user can define “custom” rainfall distributions. The user can either assign the same rainfall to all subbasins or vary the rainfall on a subbasin-by-subbasin basis.

Follow the steps below to select the rainfall distribution or create custom rainfall distributions in the CivilGEO software:

GeoHECRAS

1. From the Input ribbon menu, select the Unsteady Flow Data command.
   
2. The Unsteady Flow Data dialog box will be displayed.
   
3. From the Meteorology Data panel, select the Precipitation Data checkbox subpanel.
   
4. Select the Rain Gage Data radio button option and then click on the […] button under the Rainfall Distribution column.
   
5. The Rainfall Distribution dialog box will be displayed.
   

GeoHECHMS

1. From the Input ribbon menu, select the Meteorology Data command.
   
2. The Meteorology Data dialog box will be displayed.
   
3. From the Precipitation type dropdown combo box, select the Rainfall Distribution option.
   
   Refer to this article in our knowledge base to learn about other precipitation types.
4. Select Precipitation Data from the Meteorology Specifications panel selector.
   
5. The Precipitation Data panel will be displayed. Click the [Select] button adjacent to the Rainfall distribution read-only field.
   
6. The Rainfall Distribution dialog box will be displayed.
   

GeoSTORM

1. From the Input ribbon menu, click on the Storm Data command.
   
2. The Storm Data dialog box will be displayed.
   
3. From the Precipitation type dropdown combo box, select Rainfall Distribution.
   
4. The Rainfall Distribution panel will be displayed.
   
5. Click the [Select] button adjacent to the Rainfall Distribution read-only field.
   
6. The Rainfall Distribution dialog box will be displayed.
   

Note that the Precipitation type dropdown combo box entry will only be displayed when either EPA SWMM or SCS TR-20/TR-55 is selected as the hydrology analysis engine in the Scenario Manager dialog box.

The below sections explain how to define the rainfall distribution and interact with the Rainfall Distribution dialog box in the CivilGEO software.

Available Rainfall Distributions

The Available Rainfall Distributions panel lists all the rainfall distributions for various world regions in alphabetical order. Both predefined “factory” rainfall distributions and custom rainfall distributions are listed in this panel.

Select Rainfall Distribution

This section allows the user to select rainfall distributions present in the current scenario.

Note that more than one checkbox entry can be checked in the list to compare rainfall distributions in the Rainfall Distribution Plot panel.

Rainfall Details

The Rainfall Details section provides various details for the currently selected rainfall distribution.

The following options are available in this section:

• Storm duration
  This entry field defines the total duration of the storm, in hours. Note that this entry is read-only for time-based rainfall distributions and editable for percentage-based rainfall distributions.

• Storm minimum duration
  This read-only field defines the minimum duration of the storm, in hours.

• Storm maximum duration
  This read-only field defines the maximum duration of the storm, in hours.

Custom Rainfall Distributions

The Custom Rainfall Distributions panel allows the user to define custom rainfall distributions not included in the software’s rainfall distribution database.

The following sections are provided in this panel:

Select Rainfall Distribution

This section lists all the custom rainfall distributions that are defined. The custom rainfall distributions are also listed in the Available Rainfall Distributions panel.

Importing and Exporting Custom Storm Distributions

The software allows the user to share custom rainfall distributions with other users using the [Import] and [Export] buttons.

Clicking the [Import] button will display the Open dialog box. The user can import *.storm_dist file type, which can contain one or multiple rainfall distributions. When importing a rainfall distribution file with rainfall distributions that are already contained in the software, the software will ignore the duplicate rainfall distributions contained in the imported file.

Clicking the [Export] button will display the Export Custom Storm Distributions dialog box. This dialog box allows the user to export all the custom rainfall distributions that are defined.

Rainfall Distribution Specifications

This panel contains fields that define the custom rainfall distribution. The fields display the details of the already defined custom rainfall distribution selected in the Select Rainfall Distribution section. Additionally, it also allows the user to add, edit, or delete custom rainfall distribution.

Note that the fields in this panel are read-only by default. The fields will become editable by clicking the [Edit] or [Add] button.

The following fields are available in the panel:

• Name
  This entry field is used to define the unique name for the rainfall distribution. Duplicate names are not accepted.

• Data type
  This dropdown combo box is used to select the type of rainfall distribution data that will be defined. The following options are available to define the rainfall distribution data:

• • Time-based: For time-based rainfall distribution data, the user needs to define the storm duration. For example, 24-hours.
  • Percentage-based: For percentage-based rainfall distribution data, the user needs to define storm duration and a storm duration range.

Based on the option selected by the user, different parameters will be provided to the user for additional information.

• Storm duration
  This entry field is used to define the total duration of the data being defined.

• Minimum duration
  This field is used to define the minimum length of the storm in hours.

• Maximum duration
  This field is used to define the maximum length of the storm in hours.

• Time step
  This entry field is used to define the increment to be used in the Time (hours) column of the data grid provided in the Storm Distribution Rainfall panel. This entry converts to the Percentage step entry for percentage-based rainfall distributions. The user can then define the percentage step increment of percentage-based rainfall distribution data.
  
• Description
  This textbox area is used to describe the custom rainfall distribution in detail.

Clicking the [Edit] button allows the user to edit the already defined custom rainfall distribution selected in the Select Rainfall Distribution section. On clicking the [Edit] button, the [Cancel] button is replaced with the [Update] button, and the [Edit] button is replaced with the [Cancel] button. After editing the field values, the user can click the [Update] button to save the changes.

Clicking the [Add] button allows the user to define a new custom rainfall distribution to be added to the Select Rainfall Distribution section.

On clicking the [Add] button, the fields become editable. The user can define the data for the new custom rainfall distribution and then click the [Add] button again to add this rainfall distribution to the Select Rainfall Distribution section.

The user can cancel defining the custom rainfall distribution by clicking the [Cancel] button.

The user can also create a copy of or delete the currently selected custom rainfall distribution using the [Copy] and [Delete] buttons.

Storm Distribution Rainfall

This panel contains a data grid that is used to store the fractional rainfall data for the custom storm distribution.

The total number of rows in the data grid is calculated using the Time step and Storm duration values.

Total rows in the data grid= Storm duration x Time step + 1

The following columns are provided in the data grid:

• Time (hours)
  The content of this read-only column is automatically computed based on the defined Time Step and Storm Duration
• Fractional Rainfall Intensity (per-hour)
  This column is used to enter the custom rainfall intensity data. It accepts values between 0.0 and 1.0. The user can also copy and paste spreadsheet data into this column.

Favorites

The Favorites panel allows the user to store the predefined rainfall distributions that are used on a regular basis.

The user can select a favorite rainfall distribution and add it to the Favorites panel. In this manner, the user does not have to scroll through the general listing in the Available Rainfall Distributions panel each time a model is set up.

To add a rainfall distribution to the Favorites panel, the user can select the rainfall distribution from the Available Rainfall Distributions panel. Then, right-click and choose the Add to Favorites option from the displayed context menu. The rainfall distribution will be added to the Favorites panel.

If the user wants to remove any rainfall distribution from the Favorites panel, select the entry and then right-click and choose Remove from Favorites from the displayed context menu.

Rainfall Distribution Plot

The Rainfall Distribution Plot panel on the right side of the dialog box displays a plot for the selected rainfall distribution(s).

Rainfall Distribution Data

The Rainfall Distribution Data panel shows a data grid with information that is contained in the graphical plot. Note that there are separate data grids for each rainfall distribution since each may have a different Time step and/or Storm duration defined.

The user can right-click anywhere on the data grid to display a context menu. The context menu provides various commands to copy the data to the Windows clipboard and export the data to a spreadsheet or pdf document.

Assigning Rainfall Distribution

Once the desired rainfall distribution is selected, the user can click the [Assign] button. The selected rainfall distribution will be assigned for the meteorological model.

Note that only one rainfall distribution can be selected from the Available Rainfall Distributions panel or the Custom Rainfall Distributions panel. If no rainfall distribution or multiple rainfall distributions are selected, then the [Assign] button is disabled.