Major/Minor design for a street drainage system at Gymea, NSW, using the rational method
This runs with the 'Gymea Rational Method' selected as the hydrological model in Project → Hydrological Model.
The models include the same pipe and catchment system as in earlier examples. In the first model, the rational method procedure from the urban drainage chapter of Australian Rainfall and Runoff 1987 is selected in place of models that calculate hydrographs. Hydrological Models and Rainfall Data inputs in the Project menu are different, as are the data for the sub-catchments. The calculation procedure includes a search process to explore flows calculated at a range of times, thus avoiding partial area problems normally associated with the rational method. No hydrographs or water levels graphs are produced, only peak flowrates and water levels. Detention basins cannot be modelled.
Results from this rational method model are similar in most respects to those from the earlier examples, although the peak flows are lower, being calculated from rectangular rainfall blocks rather than the Australian Rainfall and Runoff rainfall patterns used by the Horton (ILSAX)
and ERM hydrological models.
The second DRAINS model updates the rainfall inputs using 2016 IFD rainfall data from the BOM website and the ARR Data Hub. The results from the models can be compared, but be aware that the 2016 rainfall intensities are significantly lower than the 1987 ones, and that the 2016 pervious area runoff coefficient is lower. As with the first example, you can inspect conditions in overflow routes, such as that shown below, and export spreadsheets and long-sections.
The models also include ERM models.
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