"Probably water coming up out of storm drains.) "
Water from storm drains in the city could not possibly fill these canals. Only a pump can raise water to a higher level. Water simply cannot flow from a lower to a higher and back to a lower topo region.
Having stood at the foot of a nearly topped levee, augmented by about five feet of sandbags, maybe 25 feet below water level, on a mostly dry street, watching the entire wall "breath" with the flow of the water on the other side, I can tell you for a certainty that water does somehow find a way to rocket out of the storm drains down on your level, to the extent that the folks in charge had erected a three foot wall of sandbags around the "fountain", not to stop the water coming from the drains (if you tried the pipes would simply rupture elsewhere in an uncontrollable manner) but to allow it to trickle down the street instead of making a surge which would wreck most everything it came in contact with.
In fact, the top of the "fountain" is almost certainly equal to the water level on the "canal" side of the levee, minus "pipe friction".
This is consistent with the 0300 anecdotal language in the reports. Water problems, but not quite general flooding, not yet, not at that point in time.