I've a feeling based on no knowledge at all, that a 4.5 kilometer river cave must be either fed from a very large river, or a very large amount of small streams, which I would imagine is more likely in a forest environment (again assumption based on zero experience or knowledge). Diverting all of them to somewhere that doesn't find it's way back into the cave will be surely impossible, diverting lots of them may have little effect, but if they have so many people in attendance, maybe every little helps?
When they were first found I've got to say I thought the job was all but done, then you look at the situation, 11 children who can't swim, 4.5 kilometers under ground, past flooded sections with a river to contend with, they've not eaten much for a week, possible language barrier, it adds up to a herculean task.
Keep at it team, you've got this