Rational method Check HGL outputs
Detailed results from rational method calculations can be obtained in tables suitable for checking using the Copy Check HGL to Spreadsheet option in the Edit menu. Currently a 56-column output is provided, illustrated by the example shown below.
Information on approach flow characteristics in is presented in Columns L to O. The information on pit pressure changes is shown below, with the QUDM Chart number and the ratios used to derive the K values being noted in Columns AH and AI.
Note that this table does not exactly reproduce the DRAINS results given in the spreadsheet Results output in the Edit menu, which is based on extensive calculations that cannot be practically duplicated by hand. The check calculations should be viewed as a conservative, parallel set of calculations to the DRAINS computations. If the results they portray are considered to be inadequate, the model can be changed manually.
A Rational Method Output Converter Spreadsheet, available for download on www.watercom.com.au, converts rational method Check HGL outputs from minor and major runs into formats in QUDM and in manuals prepared by Brisbane City Council and Pine Rivers Shire Council (now part of the Moreton Bay Regional Council). Macros in the spreadsheet re-arrange the results to produce an output such as that shown below:
There is also a more general spreadsheet named DRAINS Output Converter.xls, which also processes rational method data.
The Main worksheet contains instructions and runs the macros that convert DRAINS outputs in the worksheets with yellow tags to reformatted sheets with the green tags.
Related Articles
Rational Method
Developed in the 19th century, the rational method is the most widely-used hydrological procedure for estimation of design flowrates. It employs the equation: Q = C.I.A / F where Q is a peak flowrate in m3/s or L/s, C is a dimensionless runoff ...
Rainfall data for Rational Method property sheet
This window is used to enter ten values that define the key average recurrence intervals (ARIs) and rainfall intensities required to define the intensity-frequency-duration relationships to be used in rational method calculations. The ARIs entered ...
Extended rational method (ERM)
A hydrological model that produces hydrographs, such as the Horton (ILSAX), RORB, RAFTS and WBNM models, must be applied to analyse the storage routing effects of detention basins. The rational method is not suitable because it only calculates peak ...
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 ...
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 ...