Two versions of this property sheet are shown below.

ARR Project Options

• The calculation time step is the time interval at which DRAINS calculates flows coming from catchments and determines hydraulic grade line positions throughout the system. In the box to the left you can nominate whether DRAINS is allowed to set a value, or whether you wish to set your own time step. Before performing a run, DRAINS may produce a message recommending a time step less than the value that you specify here.
  

• Default pit inlet blocking factors can be specified for sag and on-grade pits. These factors are applied to specified inlet capacities specified in the Pit Database.

• The rainfall multiplier can be used to raise or lower all of the rainfall intensities provided in a model to perform sensitivity tests. In larger catchmants it may include areal reduction factors of the type described in Chapter 4 of Book 2 of ARR 2019. Note individual sub-catchments can also have their own individual rainfall multipliers specified in the custom storms property sheet.
  

• The simulation time multiplier allows the DRAINS solver to extend the overall simulation time. The default value is 1.5, which generally means 1.5 times the storm duration for small models. Other factors may extend the simulation time, such as larger models, lag times or the inclusion of detention basins. If the user is required to extend the overall simulation time (e.g. to ensure a detention tank is fully drained during analysis), increase the multiplier.

• The Pipe Friction Formula buttons allow you to choose which friction equation is to be used. For pipes there is a choice of two equations, while Manning’s Equation is mandatory for open channels in DRAINS. The Colebrook-White Equation is generally favoured for pipes in Australia, and the Manning’s Equation for open channels.
  

In the second column,

• The minimum pit freeboard is a distance below the street level in a drainage pit, above which water levels should not rise in Design runs. A value of 150 mm is commonly used in Australian practice.
  

• The minimum fall across pits is another design parameter, defining the difference in level that is often base of a stormwater pit in the direction of flow, to encourage the flushing through of sediments and debris.

• Minimum clearances between other services and pipes can be specified, for use in DRAINS design calculations that allow for these.

• The option buttons below allow you to determine whether pipe diameters can decrease in the direction of flow during runs in Design runs. Usually, pipe sizes are not allowed to decrease because of possible blockages, but this condition might be relaxed in certain situations.

In the third column,

• Using the buttons labelled For Detention Basins specify, you can choose between specifying an elevation-surface area relationship and an elevation-volume relationship for detention basins.

• Below, there is a choice as to whether the chainage is to increase in the upstream or downstream direction. This is important if a DXF drawing of a pipeline is to be exported.

• Below this are the Design Storm Procedures options. Selecting ARR v4 (2019+) will reveal additional options below including For major/minor storms select and Storm Results. The Other option allows users to utilise ARR87 procedures, Synthetic Storms and Custom Storms such as PMP or recorded gauge data.

• For major/minor storms selection allows the selection of Ensembles of Storms or Individual Storms.

• Storm Results allows critical results to be reported as either the Upper Median or Upper Mean.