Your location isn't shown. The tree is suited to wet positions- though possibly not flooding if the storm water run-off just sits there rather than moving over the area.
There are a few planted in my local bot garden, in a fairly low area near water and it probably gets a fair bit of run-off from higher ground there and they are doing OK (except for insect damage, sooty mould).
If you were really fearful yes I'd do a diversion but you might like to try to contact Gold Coast garden "friends" for input I'll try to find link - they seem to be very helpful folk
http://www.friendsgcrbg.org.au/

Here is a link that might be useful: info on tristaniopsis