The HMR52 Storm precipitation type of the Meteorology Data dialog box can be used to compute the probable maximum precipitation (PMP) for a watershed. The concentric ellipses are used to construct the storm spatial pattern where each ellipse represents an isohyet of precipitation depth. The storm is located over the watershed by specifying the center of the pattern and the angle of the major axis of the ellipses. Total precipitation depth is computed using a specified storm area and area-duration curves. The total precipitation depth is converted to a temporal pattern based on the selected placement of the peak intensity within the storm duration. The HMR52 storm precipitation type includes several parameters to describe the location, orientation, and temporal distribution of the storm.
When HMR52 Storm is selected as the Precipitation type in the Meteorology Data dialog box, the following data panel will be displayed for the Precipitation Data selector.
The following sections describe how to interact with the HMR52 Storm data panel of the Meteorology Data dialog box.
HMR52 PMP Storm Specifications
This section of the data panel includes the following options:
- Centered on current view extents
If the user selects this radio button, the software will pick the center of the current view extent of the Map View.
- Centered on subbasins
If the user selects this radio button, the software will calculate and pick the center of the current subbasins present in the scenario.
- Storm center
If the user selects this radio button, then clicking the [Pick] button allows the user to select the storm center on the Map View. The Latitude and Longitude for the selected location get automatically filled after the selection of the storm center. The coordinate values entered have the same coordinate reference system (CRS) as the project. Using the [Clear] button, the user can clear the selected storm location.
- Storm preferred orientation & Storm actual orientation
The preferred and actual storm orientation angles are measured in degrees increasing clockwise from North. Click the [Retrieve] button to retrieve the storm preferred orientation for the selected location. Clicking the [View] button displays the HMR52 Storm Preferred Orientation dialog box to view the storm preferred orientation data.
- Peak intensity
This dropdown combo box entry is used to select the 6-hour peak intensity for the HMR52 storm. This peak intensity parameter specifies the period within the 72-hour storm when the precipitation will be the greatest. The 6 hours of peak intensity can be set to begin as early as hour 24 of the storm or as late as hour 60 of the storm. The depth of rain falling during the period of peak intensity is subdivided into 1-hour increments using the 1-hour to 6-hour depth ratio parameter.
- 1-hour to 6-hour depth ratio
This field contains the ratio of the 1-hour to 6-hour depth during the 6-hour peak intensity period. The depth of rain falling during the period of peak intensity is subdivided into 1-hour increments using this parameter.
- Probable maximum storm area
This field specifies the total storm area.
HMR51 Depth-Area-Duration PMP Estimates
The table under this section allows the user to enter the precipitation depths from the HMR51 PMP (Probable Maximum Precipitation) data corresponding to different storm sizes and storm durations.
Clicking the [Retrieve HMR51 PMP Data] button will cause the software to interpolate the values for the HMR51 Depth-Area-Duration PMP Estimates table.
Clicking the [View HMR51 PMP Data] button will display the HMR51 PMP Data dialog box that displays the graphical plots of the HMR51 PMP rainfall data.