The flume, the ditch, and the wing-dam, are the chief tasks of the river-miner.
Granger was attending to the flume which they had constructed.
If that's lost the whole expedition will be up the flume, as we miners used to say.
A flume had to be constructed before it could again be used.
And what's the use of the gold in the ground when the flume isn't there to work it out?