Design Rainfall Data System (2016)

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Disclaimer & Coordinates Caveat

Before proceeding, read The Bureau of Meteorology's Conditions of Use.

Data are derived automatically from the 0.025° grid using the values at the nearest grid cell to the input location. In general the location of the data produced will not match exactly that of the input location. To guard against the possibility of accidentally entering data incorrectly, it is essential that users check that the latitude and longitude on the chart and table produced correspond (to the nearest 0.025°) to the location required. The map preview can also be used to verify the coordinates.

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How to use the design rainfall system for a single point search

The new design rainfalls (including the Intensity-Frequency-Duration (IFD) design rainfalls) are retrieved through coordinate-based searches using the following method.

  1. Start a new single point search by selecting the Single Point Search option Single point search selection in menu
  2. Enter your location information in the Search panel. To choose a type of location coordinate, select one of the following:
    • Decimal degrees: Fill in your latitude and longitude. While the system will accept both positive and negative degree values, it will assume a southern latitude and an eastern longitude so the coordinates valid over Australia.
    • Degrees, Minutes, Seconds: Fill in your latitude and longitude as degrees, minutes and seconds. Take note of the degrees sign information above.
    • Easting, Northing, Zone: Fill in your easting, northing, and zone number.
  3. If desired, enter text into the label field which will be printed on the generated design rainfall table and chart, to help you identify your results.
  4. 'Map Preview' will show the submitted location on a map for you to review.
  5. Select 'Submit' once you are happy with the location. The default table will be displayed.
  6. Select the probability range applicable for your project.
    • Very Frequent - 12 EY to 0.2 EY
    • IFDs (Frequent and Infrequent) – 1 EY to 1% AEP
    • Rare – 1 in 100 AEP to 1 in 2000 AEP
    Find out more about the probability terminology here
  7. Update the standard and non-standard durations to suit your analysis requirements.
  8. Select 'Update' to apply these changes.
  9. The design rainfall values for the location have now been extracted. You can view it as a table, or a chart (graph of data). The date of issue is included for reference.
  10. The 'Reset' button will remove any user-specified modifications and return to the default settings.
  11. The table and chart can be downloaded as per the additional instructions under 'Downloading design rainfalls and coefficients'.

How to use the design rainfall system for a multiple point search

For larger projects, multiple points can be included in a single search.

  1. Start a new multiple point search by selecting the Multiple Points search option Multiple point search selection in menu
  2. Upload a .csv file containing up to 50 points. Example templates are provided for the following coordinate types:
    • Decimal degrees: Fill in your latitude and longitude. While the system will accept both positive and negative degree values, it will assume a southern latitude and an eastern longitude so the coordinates valid over Australia.
    • Degrees, Minutes, Seconds: Fill in your latitude and longitude as degrees, minutes and seconds. Take note of the degrees sign information above.
    • Easting, Northing, Zone: Fill in your easting, northing, and zone.
  3. The .csv will be checked on upload to make sure that it is the correct format. The list of points will be displayed on upload for review.
  4. Select 'Submit' once you are happy with the list. The default table will be displayed for the first point only.
  5. Select the probability range applicable for your project.
    • Very Frequent - 12 EY to 0.2 EY
    • IFDs (Frequent and Infrequent) – 1 EY to 1% AEP
    • Rare - 1-in-100 AEP to 1-in-2000 AEP
    Find out more about the probability terminology here
  6. Update the standard and non-standard durations to suit your analysis requirements.
  7. The design rainfall values for the first location only are now displayed for review. You can view it as a table, or a chart (graph of data). The date of issue is included for reference.
  8. The 'Reset' button will remove any user-specified modifications and return to the default settings.
  9. The table and chart can be downloaded as per the additional instructions under 'Downloading design rainfalls and coefficients'.

Include a label for a point

Enter information into the label field to help you identify your selected location. This label will be displayed on the exported chart image heading and the .csv file header. It will also be used to name any downloaded files to differentiate them from previous downloads.


Non-standard Durations

Non-standard durations can be added through the 'non-standard durations' section under the Analysis tab in Minutes or Hours. Click the '+' to include additional non-standard durations.

non-standard durations option section

User-defined non-standard durations may be rounded to the nearest minute. The rounded value will be displayed in the Design Rainfall table. The rounded value shown in the results table is the value used in calculations, and therefore may differ slightly from the entered value.

Select the 'Update' button to update the list of non-standard durations.


Change design rainfall units

The new design rainfalls are displayed in units of depth in millimetres (mm) by default. There is an option to change the units if you require design rainfall values in intensity, in millimetres per hour (mm/h). This functionality is located on the web page above the table or chart on the right-hand side.

Rainfall depth and rainfall intensity are related as follows:

  • intensity (mm/h) = depth (mm) / duration (hours)
  • depth (mm) = intensity (mm/h) x duration (hours)

Display coefficients

The polynomial coefficients underlying the design rainfalls can be displayed for point locations.

These can be displayed for all locations by selecting the check box for Coefficients, under 'Other Options' at the bottom of the 'Analysis' panel.

Select coefficients option in other options

To calculate the design rainfall depths from the coefficients, use the following equation:

DepthP = e^(C0 + C1 ln(T) + C2 ln(T)2 + C3 ln(T)3 + C4 ln(T)4 + C5 ln(T)5 + C6 ln(T)6)

Where:

  • Depth = Design Rainfall for the specific probability and duration (in mm)
  • P = Probability
  • Cx is the polynomial coefficient (0 – 6) extracted from the coefficient grids
  • T = duration (in minutes)

Please note that there are two sets of coefficients for the Rare design rainfalls (1 in 200 – 1 in 2000 AEP). The daily coefficients should be used to estimate rare design rainfalls from 1 day to 7 days, while the subdaily coefficients should be used to estimate the rare design rainfalls from 1 minute up to 1 day. As different methods were used to derive the two sets of rare design rainfalls, there are two different polynomials for each standard probability which will give incorrect results if extrapolated outside the appropriate range of durations. There is only one set of coefficients for each of the standard probabilities in the Very Frequent and IFD probability ranges (12 EY – 1% AEP) which applies to all durations from 1 minute to 7 days.

For more information on using the coefficients, please see the FAQ.


Apply winter factor

Winter factors have been estimated for those parts of Australia which experience winter dominated rainfall (May to October). In these areas, rainfall events in winter tend to be small and more frequent while the larger events tend to occur in the summer months (for example ex-tropical storms).

The winter factor can be displayed for relevant locations by selecting the check box for seasonality, under 'Other Options' at the bottom of the 'Analysis' panel.

Select seasonality option in other options

To calculate winter design rainfall depths for areas with winter dominated rainfall patterns the following equation is used:

Winter depth[aep,duration] = Design rainfall depth[aep,duration] x winter factor[aep,duration]

  • For AEPs more frequent than 50%, use the 50% AEP winter factor.
  • For durations less than 1 day, use the 1 day winter factor.
  • For durations between 1 day and 7 days, linearly interpolate the winter factor.

For more information on the seasonality guidance, please see the FAQ.


Downloading design rainfalls and coefficients

Design rainfalls can be downloaded and printed in several formats.

Download design rainfall table as CSV iconDownload as CSV: Allows the user to download the design rainfall table as a CSV file.

Download all designs as CSV iconDownload all design CSV: Allows the user to download a complete design rainfall table containing all probabilities as a CSV file.

Download design rainfall chart as PNG iconDownload as PNG: Allows the user to download the design rainfall chart as a PNG file.

Download coefficients table as CSV iconDownload Coefficients: Allows the user to download the coefficients table as a CSV file.

Print screen iconPrint Screen: Opens a print dialogue on a separate screen.

You also have the option of saving the table or graph first and then printing those files directly.

For the multiple points search, a ZIP file containing the design rainfall tables or charts can be downloaded using the

Download all CSV icon

Downloads a ZIP file containing tables of design rainfall depth and intensity for all three design rainfall probabilities ranges for each point, including the coefficient tables.

Download all PNG icon

Downloads a ZIP file containing charts of all three design rainfall probabilities ranges for each point.


Downloading design rainfalls (grids)

Grids for standard probabilities and durations are available for download through the design rainfall system.

  1. Start a new Extent grid search by selecting the Extent search option
    Single point search selection in menu
  2. Enter your location information in the Search panel for the Lower-Left and Upper-Right corners of the rectangular extent. To choose a type of location coordinate, select one of the following:
    • Decimal degrees: Fill in your latitude and longitude. While the system will accept both positive and negative degree values, it will assume a southern latitude and an eastern longitude so the coordinates valid over Australia.
    • Degrees, Minutes, Seconds: Fill in your latitude and longitude as degrees, minutes and seconds. Take note of the degrees sign information above.
    • Easting, Northing, Zone: Fill in your easting, northing, and zone number.
  3. Select 'Submit' once you are happy with the extent. Note that no data will be displayed in the results panel.
  4. The following design rainfall grids are prepared for the selected extent, available through the download buttons at the top of the page: Each of these probability files includes design rainfall grids of depth in millimetres for all standard durations in ascii format. They are downloaded through the browser as a .zip file. This may take some time. Please keep this page open while the download completes.
  5. The file naming convention is as follows:
    catchment_depth_(duration in minutes)min_(probability in aep)aep.txt.asc

Standard durations
1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 45 minutes
1, 1.5, 2, 3, 4.5, 6, 9, 12, 18, 30, 36 hours
1, 2, 3, 4, 5, 6, 7 days

Probability range Probability Probability Label

Very frequent

 12 EY 99999aep
6 EY 99752aep
4 EY 98168aep
3 EY 95021aep
2 EY 86466aep

Very Frequent and IFD

 1 EY 63212aep
2 year ARI 39347aep
5 year ARI 18127aep

IFD

 50% AEP 50000aep
20% AEP 20000aep
10% AEP 10000aep
5% AEP 05000aep
2% AEP 02000aep

IFD and Rare

 1% AEP 01000aep

Rare

 1 in 200 AEP 00500aep
1 in 500 AEP 00200aep
1 in 1000 AEP 00100aep
1 in 2000 AEP 00050aep

Select point/s or extent from map

If you are not sure of the coordinates of your locations, there is a map search tool that can be used to select points or an extent.
Note: this functionality is not available for Internet Explorer Version 11 or below. Another browser will be needed to access this map selection tool.
The following information is available on the map to help to identify locations:

  • Land area
  • Main roads
  • Localities
  • Watercourses
  • Design rainfall grid cells
  • Catchment boundaries (optional)catchment icon

To select point/s:

  1. Navigate around the map to the required location. Use the +/- buttons or scroll to zoom in/out, click and pan to move around.
  2. Select the POINTS search optionmappointsicon
  3. Click on the map to add points. This will be shown on the map and a list will be created in the Search table on the left with the latitude and longitude for each point.
  4. Points can be removed by selecting the mapremoveiconbutton and clicking on the point/s to be removed.
  5. Click Submit once the list of points is complete.
  6. Further instructions on completing the multiple point analysis can be found under the sections Non-standard durations and Downloading design rainfalls and coefficients (points).

To select a rectangular extent:

  1. Navigate around the map to the required location. Use the +/- buttons or scroll to zoom in/out, click and pan to move around.
  2. Select the EXTENT search option mapextenticon. The pan function will be disabled once EXTENT is selected so make sure that the display shows the full catchment extent.
  3. Click and drag on the map to add an extent. A rectangular box will be shown on the map defining the selected extent and the latitude and longitude of the top left and bottom right is shown in the Search box on the left.
  4. The extent can be removed by clicking mapextentremoveicon. Only one extent can be selected at a time.
  5. Click Submit once you are happy with the extent.
  6. Further instructions on completing grid extent analysis can be found under the section Downloading design rainfalls (grids)".

Undertake observed rainfall comparison

A storm envelope calculated based on rainfall from observed storm events can be plotted against the design rainfalls for a single point. This forms an estimate of the probability of the rainfall event being equalled or exceeded in any given year.

  1. Obtain rainfall data and calculate storm envelope for relevant durations. The storm envelope consists of the maximum observed rainfall recorded for a duration during the storm event. This duration is a sliding window across the whole event.
  2. Undertake a single point search for the location of the rain gauge and submit location.
  3. Expand the Observed Rainfalls tool under the Analysis tab
    observedimage
  4. Enter the maximum rainfall values for the standard durations relevant to your project. Not all durations have to be filled in. Note that observed rainfall comparison is limited to the standard durations. Non-standard durations cannot be included in this comparison. Click update to add these to the design rainfall table and chart. The IFD probability range appears as the default.
  5. The observed rainfall depths will be shown in the right hand column of the table, along with the estimated probability range for each duration. These are also plotted on the chart with black points and a line. The results can be downloaded as part of the design rainfall table and chart to include in reports. The observed rainfall values can be transferred to the Very Frequent and Rare probability ranges by selecting the appropriate radio button and then updating the table again.