Getting a stream to pass under a new canal? The term used locally is "chunker", and the conduits were made traditionally using elm planks to make some sort of a covering structure before the canal earthworks pass over the top of it. Elm chunkers have been known to last 200 years. It would be better these days to use something like polypropylene pipes or maybe even concrete these days, assuming that there were no heritage constraint applied to the operation that might prevent hese materials being used.

If you google - inverted syphon - the second find is your question on CR4, the third one is this site . It seems to be what you are looking for.

Google,_{google, google.........}

What is in your pipe? Gravity flow or rising main?

Few points to remember.

For channel to channel syphon the outlet side must be lower than the inlet side to allow for friction losses.

It is best to have the pipe below the riverbed to prevent impeding and storm water damage.

If the pipes are above the bed ample protection must be provided.

In SA and possibly elsewhere you may need authorization.