Sub-Catchment property sheet (superseded)

Sub-Catchment property sheet (superseded)

The older form of the property sheet for Horton (ILSAX) sub-catchments is shown below. A similar form of model was used with the rational method and extended rational method procedures, with the land-use types being impervoius and pervious, rather than the paved, supplementary and grassed classifications shown below.

The main difference for the current property sheet is that in the Hydrological Model buttons there is a comprehensive data option, in addition to the abbreviated data and  more detailed data options.  This allowed for three flow path segments, with the last covering flows along street gutters, with the user specifying gutter length, slope and a GUT factor that included the geometric characteristics of the street cross-section. From this a time of flow could be calculated, using equations that assumed a given depth of flow, usually the kerb height.

With the comprehensive option, the times determined are additive and relate to different flow paths. For a paved area, the times involved are:

a constant time, which can represent property drainage time (all options)

+ an overland flow time calculated from length, slope and roughness (more detailed data or comprehensive data options)

            + a gutter flow time based on length, slope and gutter factor (comprehensive 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). The gutter roughness factor allows for the gutter cross section and roughness.

For a supplementary area, the times involved are:

  a constant time (all options)

    +  an overland flow time calculated from length, slope and roughness (more detailed data or comprehensive data options).

For a grassed area, the times involved are:

  a constant time, which can represent property drainage time (all options) 

   + an overland flow time calculated from length, slope and roughness

(more detailed data or comprehensive data options)

With the abbreviated data or more detailed data options, a grassed area lag time could be selected.  However, if the comprehensive data option was selected, this was replaced by a lag factor that takes a value from 0.0 to 1.0. This allows because the time of entry to vary with different rainfall intensities, because it is based on paved area times that may be calculated by the kinematic wave equation.

The complexity of this form of entry confused many users and it was decided to simplify DRAINS my removing the comprehensive data option for new models. Where this option has been used in older models it will still work in DRAINS.

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