Rational & Extended Rational Method (ERM)
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 ...
Runoff coefficient, C
This is the factor used in the Rational Method to allow for a number of influences on the conversion of rainfall to runoff. Such influences include loss and routing effects, and the effects of land-use, catchment slope and other factors. The ...
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 ...
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. ...
Partial area effect
In rational method calculations, the storm duration used to define a rainfall intensity of a given average recurrence interval is commonly set equal to the time of concentration of the catchment. This is based on the assumption that, in the rational ...
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 ...
Standards Australia rational method design procedures for property drainage
The Australian and New Zealand standard, AS/NZS 3500.3:2015, Plumbing and Drainage, Part 3: Stormwater drainage, provides design, installation and other information for roof and property drainage systems. The design method for surface drainage ...