Design runs

Design runs

(a)  General

Design in DRAINS involves the determination of the characteristics of the components in a drainage system. This can be by trial and error, or by use of an automatic pipe system, such as that provided in DRAINS.  The design is than checked using an analysis or simulation of flows through the system, involving hydrological and hydraulic calculations.


Different hydrological models can be applied to design, as described here.  A new initial loss - continuing loss model has been presented in Australian Rainfall and Runoff 2019, but is still incomplete. Older models such as Horton (ILSAX), the rational method, extended rational method and storage routing models can still be applied.

To use the design procedure, first choose the relevant option in the Run menu. This runs the program and if no problems are encountered, a message appears advising that the process is complete and that you should analyse with minor or major storms to assess the results. You can do this by choosing from the available analysis options:

  • for models set up with versions of DRAINS released prior to 2011, the superseded basic hydraulic model.

The basic hydraulic model is now obsolete, but can still be used to obtain results from earlier DRAINS models and to compare results from the hydraulic model alternatives.

The Design procedure selects suitable pit inlets from the sizes available for the selected pit type and chooses pipe diameters from those available in the pipe data base for the type of pipe specified.  If a pipe system is to be designed, it is run using the Design option in the Run menu, and then followed by simulations of the system's behavious in various storms, using the Analysis options.  It is not used when a drainage system is existing and pipe characteristics are fixed, or for open channels or detention basins.

An enhanced design method was introduced in 2014, and a more complex ARR 2019 design procedure involving ensembles of rainfall patterns was introduced in early 2017.  This can also be applied in DRAINS.     

(b)  Further information

Design is the process of defining the basic characteristics of some object or system, for the purpose of creating this system. In engineering, it involves the use of a suitable model and calculations. For stormwater drainage applications, it determines the layout, position, type and size of the components of a drainage system.   Design is one of the main modes of operation of DRAINS.  Until 2011, there were two procedures available, the Standard Design method and the Advanced Design method.  Now only the advanced method is available, simply called 'Design' in the Run menu.

If you were to apply DRAINS to a greenfields subdivision drainage system design, you might work out the plan of the system on a paper plan, or more likely, using a CAD or DTM program.  You might also use the links between DRAINS and the DTM programs 12d, Civil 3D or Civil Survey Solutions’ Civil Site Design for this purpose.  You would then set up a DRAINS model, probably with a background showing street layout and cadastral data.  You would probably take this from a pre-existing base file that already contains the hydrological, rainfall, pipe, pit and overflow route information that you need, in data bases accessible from the Project menu.   It is likely that the pipe layout and background would be imported from a suitable CAD file.

Following procedures in design manuals such as Australian Rainfall and Runoff (I you would set up a set of minor storms, which define the conditions that are to be addressed in sizing drainage systems.  You would also set up a set of major storms, to be used to check that the system 'fails safe' in severe conditions.  Minor storms may have average annual exceedance probabilities (AEPs) of 50% to 5% or average recurrence intervals (ARIs) of 2 to 20 years, while major storms are usually set at 1% AEP or 100 year ARI.

After running the DRAINS model using the design method, and checking this with an analysis using minor storms, you can alter the pipe system to refine the design  (DRAINS provides designs that meet the design requirements, but there may be some overdesign). You could then transfer the system data (containing the data entered through property sheets, plus designed pipe sizes and invert levels, and x-y coordinates of pits and nodes), to a spreadsheet program using the option in the Edit menu, and copy this on to a worksheet labelled "Data".  The results of the design run using minor storms could be transferred to another worksheet labelled 'Design' or 'Minor'.

After inspecting the design results, you could then run DRAINS with the major storms to check that the system operates safely in large storm events and transfer the results from these to another worksheet labelled 'Analysis' or 'Major'.  The three worksheets provide the documentation for the design.  You could then produce long sections of selected pipelines, and transfer these to a CAD program as a DXF file.  If you were using a DTM program, you could transfer data directly from DRAINS and use the more elaborate drawing facilities that they provide.

Designing for infill developments where constraints are imposed by existing developments and infrastructure is a more complicated process, and it may not be possible to use the automatic procedures that apply in greenfields design.  Since DRAINS operates quickly, and changes are easily made, it can be used to arrive at a solution by trial and error, the usual method of designing.

(c)  Run Details

When you choose Design from the Run menu, the following warning will appear:



This should not be a problem.  Save your input file under another name if you are worried about data such as invert levels and pipe diameters being changed.

A success full run will provide the following message:



This may be preceded by notes such as:



If a design that meets all the design requirements cannot be achieved, a message like this will appear.  




This usually means that you have been too optimistic in assuming that a pit can accept flows from a particular sub-catchment.  It will be necessary to add additional pits and to adjust characteristics such as sub-catchment areas and times of concentration.

Once a workable design has been obtained, you must check this by analysis runs from the DRAINS Run menu.

Examples 1 to 7, 9, 12 to 16 and 18 show various design situations and methods.

    • Related Articles

    • Design and analysis procedures

      Different design and analysis methods are recommended by the 1987 and 2019 editions of Australian Rainfall and Runoff. The 1987 Procedure The 1987 procedure simulates the conversion of (a) rainfall intensities to peak flowrates, using the rational ...
    • Analysis runs

      (a) General Analysis is the main mode of operation of DRAINS, in which the program performs a simulation of the operation of a drainage system during some rainfall-induced event or events, but does not change any aspects of the system that are ...
    • Civil Site Design

      Civil Site Design (formerly called Advanced Road Design) is a road design and earthworks package developed by Peter Bloomfield and Civil Survey Solutions (formerly CADApps), running in AutoCAD's Civil 3D environment. Links exist between Civil Site ...
    • Enhanced Design method

      An improved design method for pipe systems has been added to DRAINS in 2014, in response to overdesign occurring in some models. This procedure is applied for all hydrological models and rainfall patterns. The first part of this method is the same as ...
    • QUDM pipe system design procedures

      The Queensland Urban Drainage Manual (QUDM) sets out detailed pipe design procedures that include the estimation of pit pressure changes using a set of charts that includes the Missouri Charts (Sangster et al., 1958) and graphs developed by Hare ...