Rational Method Design Example with Upstream Flow Paths, for South Pine River Area, Queensland

Rational Method Design Example with Upstream Flow Paths, for South Pine River Area, Queensland

The file for this example, South Pine R. Rational Method - US Flow Paths.drn, is located in the folder C:\ProgramData\Drains among the Lite examples. If this folder is hidden, in File Explorer select the View tab and tick the Show Hidden Items box to make it visible.  

This rational method example shown below, set up with 2016 I-F-D data, transposes the earlier Gymea example to the Brisbane area, adding nodes and overflow routes above the top pit of each pipe branch (Pit A.1, Pit A.2, Pit B.1 and Pit C.1). These additional components allow the designer to assess approach flows to pits at the tops of pipelines, by specifying suitable percentages of the downstream sub-catchment flows that are to be added to the zero overflows from the upstream nodes (these percentages vary depending on the system layout and allow for the combination of overflows with runoff from the downstream sub-catchment through which the overflow passes).


Note that if you run this model using a hydrograph-producing models such as Horton (ILSAX) and ERM, there will be two red numbers in each upstream overflow route where you specify a percentage of the downstream catchment. The first will be  the flow at the top of the route, and the second the flow at the downstream end. Only the top flowrate is shown with the rational method.

A spreadsheet converter available from www.kustomengineering.com.au, named DRAINS Output Converter, can be used to set out rational method, Horton (ILSAX) and extended rational method results in the table shown  below. This incorporates the procedure for defining pressure change coefficients at pits, based on charts provided in the Queensland Urban Drainage Manual, 2013.  This has been updated to work with the ARR 2019 IL-CL model.