I have heard that all utilities, including electricity, were out of commission during the hurricane. Perhaps compressed gases might act as freezing agents but this would be a whole new element in the infrastructure and probably quite an expensive addition.

I like the idea, but would the ice crack the concrete parts of the levee which were still intact and weaken them structurally so that they also fail when the broken section had been repaired and the water allowed to melt.

Would it be better to dump a large amount of water absorbant chemicals similar to the type that they use to disperse clouds some distance upstream from the fast flowing break in the levee wall? It could turn the water to gel at that point staunching the flow and allowing the repair to be carried out. Would stopping the flow cause an overflow at another point in the system?

I recall seeing some floating concrete 'harbours' in a documentary about D-day, they towed them across the sea and then filled them with water to provide a stable platform where ships could be unloaded. Could you float a concrete or plastic section shaped like a house gutter pipe (half cylinder shaped) which was the same shape as the levee down to where the break was and then flood its floatation tanks so that it sank in the correct position to block the flow and carry the water past the break? It would need some very precise handling to get it into the correct position.