I live within the catchment of the Waimakariri river on the Canterbury Plains and depend on the water that flows from it.
In my exploration of the rivers upper catchment I recently explored the White River Glacier
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that is near the top of the catchment and then this last week went up The Broken River which is in the hills closer to the Plains.
Broken River forks off the Waimakariri not far up from where the plains start.
The transalpine train from the east to west coasts follows the Waimakariri across the plains river and then where Broken River forks off so does the railway. Some 10km up from that fork the railway turns into Avoca valley and ultimately rejoins the main river (Waimakariri) before going through a tunnel under the alps.
Anyway to reach this location you drive up the main state highway 73 almost as far as Cass and then turn down the Craigeburn road which takes you almost all the way back south east to Broken River. You can park at the old settlement of Avoca, where one old cottage still stands but where in the 1920s there was a working coal mine bringing coal up from Broken river to the railway and Avoca station.

From Avoca you walk up the track which follows the route of the old rail track which brought coal from the Broken River Mine to Avoca.

The track is steep at first but them levels out to an easier walk across the side of the hill toward Broken River.
Walking across the side of the valley we watched a small plane topdressing fertiliser onto the river valley flats below- superphosphate topdressing greatly increased productivity on these farms when after WW2 the technology enabled it.

When you near the Broken River the track takes another steep incline down into the river- this is where a steam engine was sited to pull the coal up from Broken River.

The walk/climb down is not for the faint hearted. On the ground is still the remains of the steel cables and rails which carried the coal wagons up and down the incline driven by the steam engine.

This is the view as you descend the ridge -

When you reach the main river at the bottom of the old coal line incline there is no formal marked track up river to the hut or to the coal mine. You must navigate via the river and some vague tracks you may find along the way. You also need to cross the river several times and if the river is up it will be impassible.

You can check the river flow online https://www.ecan.govt.nz/data/riverflow/sitedetails/66442

The river flow was about 60 m3/sec when I walked it and I would not feel confident if it was much higher.

There are some steep cliffs on the sides of the river which appear to me a mix of limestone and coal or shale seams.

It took about 2 hours to navigate the roughly 2 km upriver to the hut.

The hut is up on a low terrace above the river bed and if you miss the 4wd track that comes up from the river bed up river you will need to watch out for the rope that goes up the terrace directly to the hut.

The hut has four bunks and is free to use. The hut book indicates it is empty most of the time being off the beaten track to some extent.

It is certainly in very good condition for its age and appears to have been renovated not long ago.

I didn't manage to locate the old coal mine- although it looks close on the map the terrain is pretty intimidating once you leave the main river.