Diagnostics and tips for linked 1D urban and 2D simulations

If you are struggling to get your integrated model to run to completion, the model diagnostics will help you pinpoint the cause of the problem. The locations of these messages vary:

• User interface - a pop-up window will appear to indicate a problem.
• Running a simulation via the UI - the simulation window contains a log of all the messages from the engines.
• 1D river engine - the messages are in files with extension lf1 and/or zzd.
• 2D engine - the messages are in files with extension lf2 and/or log.
• 1D urban engine - the messages are in a file with extension rpt.
• TUFLOW - the messages are in a file with extension tlf.

General tips

If time allows, test running each component of your linked model individually to check how stable each model is.

A 2D model will need a flow boundary input to replace the 1D element, e.g. for integrating with a river network, use the link-line shapefile (or for integrating with an urban network, use the link-element shapefile) to locate the boundary flow and assign a constant flow.

Model timesteps for the 1D and 2D elements of the linked simulation are required. We recommend adopting a 1D timestep that is exactly half of the specified 2D timestep (as the 2D solver performs 2 “half timestep” calculations in the x and y directions, so 1D should correspond to this). However, if you use a different 2D timestep (possibly required to achieve stability) then this must be selected such that your 1D timestep is an integer multiple of half the 2D timestep. Please note that usually shorter timesteps are required (compared to running each element individually) to maintain stability in a linked model.

Tips on integrating urban networks

A general checklist of some considerations when integrating to urban networks is as follows:

Ensure you 'Allow Ponding'. This is necessary to allow flow back into the urban network if connecting to anything other than an outfall node. A 'Ponded Area' must also be set. You will be warned by software if there is a large difference in the ponded area compared to the area of the linked aspects.

Are your nodes compatible? Recall the default urban and 2D link (flow into the 2D) can be used for outfall, flow divider or junction nodes, connected to the 2D domain.

Use dynamic wave routing for the urban model. Ensure 'Use Variable Timesteps' in NOT checked. This is always necessary for integrating to river networks or 2D.

When integrating with 2D components watch out for vast differences in elevations. A checkbox is provided on the 2D simulation window to automatically adjust the DEM so the difference is no more than set amount.

Timesteps: 1D timesteps should match! Or at least multiples of each other. If linking to 2D, we recommended the 2D timestep is twice that of the 1D. Set your start and finish times as absolute values to match the details in the urban network.

When integrating urban networks and 2D information on the linked components will be written to the log file. This gives the user additional verification that the link lines have connected with the 1D model as intended. It also provides a readily-available summary of the data used, which is useful for informative purposes and for model debugging. This additional information is written in the following format:

No., Type, x1, y1, x2, y2, Label1, z1, z2, z1d, 1dID, 1d_Type, dom, zset, length, cd, ml
where:

• No. – index number of link line
• Type – type of link (“H”, “Q” or “W”)
• x1 – horizontal coordinate of first vertex within the link line
• y1 – vertical coordinate of first vertex within the link line
• x2 – horizontal coordinate of last vertex within the link line
• y2 – vertical coordinate of last vertex within the link line
• Label1 – 1D label of connecting node
• z1 – elevation of first vertex within the link line
• z2 – elevation of last vertex within the link line
• z1d – elevation of linked urban node
• 1dID –index of linked urban node
• 1d_Type – type index of linked urban node
• dom – domain index to which the link line applies
• zset – information on where the link line elevation is obtained; takes one of the following values:
  • DEM – elevation taken from the original topography
  • INT – elevation interpolated from the z-values input on the link line
  • SET – single elevation value applied to the link line
• length – length of link line
• cd – coefficient of discharge (weir links only)
• ml – Modular limit (weir links only)

An example of the log file format is shown below: