I-F-D (intensity-frequency-duration) relationships
This is a three-way relationship that defines the statistical distribution of rainfalls expected to occur at a particular location. It is derived from statistical analysis of rainfall pluviometers or automatic raingauges, which record rainfalls occurring over different time durations.
The term 'I-D-F' is used more commonly outside of Australia. Forms of I-F-D relationships are shown below.
They are often presented with logarithmic scales for intensities and special scales for durations.
In 2013, the Bureau of Meteorology (BOM) issued design rainfall data in the form of depths instead of intensities, producing a different type of chart that plotted depths for various durations and annual exceedance probabilities (AEPs). These were updated in November 2016 and in early 2017, I-F-D tables and charts became available for both intensities or depths, as shown below:
This 2016 data can be entered into DRAINS by a two-stage process, first downloading files containing depths and temporal patterns and then inputting these into DRAINS.
The older 1987 IFD relationships can be calculated for any location in Australia using:
- the BOM website at http://www.bom.gov.au/water/designRainfalls/ifd/index.shtml, using the latitude and longitude of the required location, in the process described here;
- nine factors corresponding to the required location, taken from maps in Volume 2 of Australian Rainfall and Runoff (1987). DRAINS can perform the necessary calculations using data entered in the IFD Data property sheet, I-F-D data was made available;
- a table or chart of IFD data from the Bureau of Meteorology or the local council that administers the place where intensities are required.
Related Articles
Obtaining 2016 I-F-D Data
The latest rainfall intensities and depths to be used in design and analysis procedures are obtained after completing the previous steps from the ARR Data Hub. If you want to obtain the 2016 IFDs separately to the ARR Data Hub click here. This ...Rational method setup with 2016 I-F-D data
Although it is not sanctioned by ARR 2019, it is likely that some designers will want to continue working with the rational method, maintaining the methods set out in the 1987 edition of ARR. This can be done in DRAINS with 2016 ...Synthetic storms for the Extended Rational Method
The extended rational method (ERM) can be applied using the design storm patterns from Australian Rainfall and Runoff 1987 used by the Horton (ILSAX) and storage routing hydrological models or using synthetic patterns derived from the local ...IFD Data property sheet
This window is used to enter nine values that must be read from charts in Volume 2 of Australian Rainfall and Runoff (1987), to define rainfall intensities for the purpose of establishing standard rainfall burst patterns to be used in the DRAINS ...ARR87 rainfall pattern dialog box
This window is used to enter rainfall storm burst patterns taken from the manual Australian Rainfall and Runoff (1987). You need to enter: the zone of Australia, as shown in Figure 3.2 of Australian Rainfall and Runoff (1987), the duration of the ...