Analysis runs

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 specified. Full details of a system must be entered for this type of run.

In the Run menu shown below, DRAINS allows for two analysis options, Analyse major storms (Lite hydraulic model) and Analyse minor storms (Lite hydraulic model) that run with all versions of DRAINS. There are also two other options, Analyse major storms (Full unsteady hydraulic model) and Analyse minor storms (Full unsteady hydraulic model), that run unsteady flow hydraulic calculations in overflow routes. These methods operate in broadly the same way, modelling flows through the drainage system with the sets of storms defined as minor and major in the Select Storms option in the Project menu.


If a model has been created with an earlier superseded basic hydraulic model, two more choices will appear, Analyse major storms (basic hydraulic model) and Analyse minor storms (basic hydraulic model), that will allow you to perform runs with this obsolete model.

Runs made using the storage routing models will all be run as simulations and so produce analyses. Rainfall data for runs with these models are organized in the same way as for Horton (ILSAX) runs, with major and minor pattern choices.

Modelling existing systems requires more hydrological and hydraulic knowledge than the design of new systems. Information for setting up models to analyse established drainage systems will come from plans, inspection sheets, aerial photographs, survey data and other sources held by a council or drainage authority, and from its asset data base and GIS. A GIS, CAD or DTM program will be needed for defining sub-catchment boundaries and areas and other inputs.

Sites will need to be inspected and unusual drainage configurations will have to be set up in DRAINS. It may take a lot of work to set up a file for a large, complicated system, but once this is established, it can easily be updated and re-run, becoming a tool for assessment of drainage system adequacy, especially in the consideration of flood-affected development sites. The spreadsheet output in DRAINS, which can also act as a data input, can be used to facilitate the editing of data, and for transferring data and results to data base and GIS programs.

(b)  Run Log

When you run, DRAINS will provide one or more messages. A Run Log that signifies that there are no problems or violations of design limits is:


If there are issues, the Run Log may appear like these below.

This run Run Log indicates that the maximum flow in overflow route OFE4 has exceeded the specified safe limits in the overflow route database and that an unsafe pond depth occurred at sag pit 'PitE1'. Additionally, a more significant issue is being flagged that overflow route OFF1 is sending water uphill. This is due to the limitation of using the Lite hydraulic model that can only model uniform flow in a downstream direction. A situation like this requires reconfiguration of the overflow route, or if the overflow route is draining into a storage (such as a ponding sag pit or basin), then analysis is required with the Full unsteady hydraulic model.



This next Run Log indicates that the maximum flow depth in overflow route o178 has spilled, exceeded the maximum specified cross section limit. This could indicate a poorly specified cross section profile in the data base, or that there are significant flow volumes in the model. If the later, than it is important to consider if the results are reflective of the situation. This might include seeing if flows should be split into multiple directions via multiple outgoing overflow routes, such as a regular overflow route from an on grade pit continuing down the road, plus a slightly higher overflow route sending water over the crown of the road, and possibly a third overflow route sending water into adjoining private properties.



You will be able to view the Run Log later, by selecting View Last  → Run Report.  It is also printed in the spreadsheet output of results.

When designing a new system, or looking for solutions to problems of an existing system, you will need to change parts of the model and make further analysis runs to arrive at a suitable solution. You can also obtain further information by inspecting Main Window displays and results for various components.

See Examples 8, 10, 11 and 17 for analysis applications. Also note that analysis is used for checking in all the design examples.

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