The Pipe Auto Size option allows a network of Pipes and or Channels to be given an initial sizing to ensure that they meet the requirements specified in the Pipe Sizing Criteria.
Note: Use of Auto Size is optional, if the levels and sizes are known they can be entered directly.
The auto size process is completed based on the Pipe Sizing Criteria specified for the phase. Some aspects, such as Minimum Cover Depth, Velocity and Slope are optional and will only be used if turned on. However the auto sizing engine will always look to ensure that a pipe/channel has sufficient capacity to take the calculated flow. Equally the Design Level will be applied to align pipe/channels to one another.
Initiating a Pipe Sizing
Note: The use of the Auto Size on the Connections form will not be committed until the 'Apply' or 'OK' button are pressed to confirm the changes. This can be useful if you wish to see the effects of Auto Size without changing the model. i.e. Click on 'Cancel'.
Auto Size Calculations
Pipe sizing will begin at the head of the Flow path selected, which acts as the mainline. Typically the head of a Flow Path will normally be an Inflow (Area or Hydrograph).It will then move down each Pipe/Channel in the network sizing the pipe/channel in turn.This is completed as follows:
If the Minimum Cover Depth is being used the calculation will ensure that the depth from the cover level to the soffit is at least the value entered. However this only applies to Pipes as Channel "soffits" are seen as aligned to the surface.
Note: It is therefore important to ensure that the cover level for each connection is present to avoid the whole network being dropped to suit an invalid level. 0m is considered a valid level for the purposes of sizing.
it is possible to lock a Pipe/Channel to prevent it being sized, by toggling the Auto Size setting (hidden by default) on the Connections form for a given connection(s). When the Auto Size calculation encounters this it will not adjust the dimensions of that connection. The Area and Base flow totals will still be determined and passed downstream and the downstream connections will still be aligned to the locked connection.
Connections without dimensions
The Auto Size calculation cannot size a connection if it does not have dimensions so it will be bypassed. In the same way as a Locked pipe/channel the software will still establish the total area and base flow so that this can be carried forward. It is however not possible to align the downstream connections against it so the previous upstream connection will be used instead.