Sub-Catchment (Rational Method and ERM) property sheet
This appears when a ratrational method or extended rational method (ERM) model has been specified as the default model in the Hydrological Model dialog box called from the Hydrological Models option in the Project menu.
The form of the box will depend on the type of rational method model chosen as a default, and specified in the Rational Method Model property sheet opened through the Project menu.
If it is a general rational method model, or the method from Australian Rainfall and Runoff 1987, you will need to insert:
a sub-catchment name and area (ha), the percentage areas impervious and pervious, and the corresponding times of concentration along the longest flow path in a sub-catchment.
Next to the Hydrological Model buttons there is another set of option buttons for selecting the level of data required as:
- abbreviated data,
- more detailed data.
With the latter option, more text boxes for data entry and display appear.
Text boxes for the impervious and pervious area surface types are arranged in two columns. In the first row, you can enter the percentages of each surface type within the sub-catchment. The following rows are for the information needed to determine times of entry or travel times.
The times determined are added and relate to different segments of flow paths. For an impervious area, the times involved are:
+ a constant time, which can represent the full sub-catchment flow time (abbreviated data option) or flows off roofs and along street gutters (more detailed data option)
+ an overland flow time calculated from length, slope and roughness (more detailed data option).
By choosing different options or by setting factors such as constant times to zero, many choices are possible. Overland flow times are calculated using the 'kinematic wave' equation described in Australian Rainfall and Runoff, 1987 (pages 300-301).
For pervious areas, the times involved are:
+ a constant time, which can represent the full sub-catchment flow time (abbreviated data option) or flows off roofs and along street gutters (more detailed data option)
+ an overland flow time calculated from length, slope and roughness (more detailed data option).
With rational method and ERM calculations, no allowance is provided for lag times or factors, as is done in the Horton (ILSAX) hydrological model calculations.
If the Standards Australia AS/NZS 3500.3 method is used, you will need to enter:
- a sub-catchment name and area (ha), and
- percentages for roofs, impervious surface areas and pervious surface areas.
You can switch between models using the You specify option in the Hydrological model box.
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