This message will arise if the length of a pipe is too short to overcome the elevation difference of the connected nodes. The image below gives an example of this message.
This condition can arise when the following happens:
1. It may be because the pipe length defined is simply too short.
2. It can arise when a user has developed a model, defined all pipe lengths and node elevations however, at a later date inserts a node forgetting to update the default elevation value of zero for the node.
It is recommended that all "Pipe Length < Elevation Difference" warning messages are resolved and the model recalculated to refresh results. If there are multiple counts of this warning, it can effect model convergence and will effect the calculated results. Resolving the warning may require updates to pipe lengths or node elevations or a combination of both.