Tiropahi/Four Mile Stream is basically a small river which has quite an impressive slot canyon, just downstream of the main road bridge. Though the actual form of the canyon itself is very straight forward, the water makes it quite a challenging Canyoning trip.
Firstly, the water is so stained with tannin, that it is pretty much like going canyoning through Coca-Cola. Even with a diving mask on, you can barely see your shoes when you peer under water. This makes it impossible to assess any pools for jumping without actually getting in them first.
Second, there is usually quite a bit of water flowing downstream. Our trip was done at 0.7m on the second (fully intact) stage gauge on the true left, about 50m downstream from the road bridge. At the end of our trip, we calculated the flow to be about 3.0 cumecs, which is quite a lot for a Canyoning trip.
In the slot, there is a lot of tree debris, which makes for quite of lot of objective hazard with regard to strainers in the significant flow. Also, there are two drops in the upper slot which need to be jumped, but you can't inspect the pool due to the opaque waters.
We solved this problem by creating some tricky temporary anchors which one of us used to absiel into the pool. That person then swam around to check the pool for depth and rock/tree obstacles before the other jumped down.
Despite having to be very wary about strainers and hydraulics, the canyon was impressively deep, narrow and beautiful!
Tiropahi running at 0.7m stage
Toine contemplates yet another nasty log jam
Toine carefully looks for strainers and hydraulics before committing to the current
This is just above the second (last) small drop in the upper slot. We were able to rig a human anchor, backed up by a temporary nut placement to rap the drop on the true left in order to scout the pool for jumping.
Toine seems happy to be out of the main slot: Celebration leap!
Once clear of the true bedrock slot section, the river turns back into boulder garden rapids, but the stream walls are still very steep and usually inescapable. The walls here on the true left are actually slightly overhanging the stream!
Carefully crossing the rapid above the 25m drop.
Inspecting the pool below the 25m drop
Chucky on Rappel. It doesn't look like much water from this angle,
so check out the angle below...
From the pool below the drop, you get an impression of how much water there is in this canyon! The waterfall was so powerful that it was creating 2 foot high waves in the pool beneath it. Definately a tricky and intimidating swim, to avoid the huge eddy that would quite like to keep you in the canyon...
Once clear of the main drop, it was just a fun boulder hop/swim down to the ocean, still keeping a careful awareness of logs and snags. Like Nic says, the return track starts on the true right, about 100m before the Ocean. it is directly opposite the very last significant (20m tall) stone bluff on the true left of the river. We found the track pretty straight forward to follow until it flattened out. We kept moving in the direction of the previous track accross the short plateau (60m) until we hit the base of a small bluff, which we followed round to the left to where the track markers begin again.
About a 4 hour round trip, though certainly NOT a trip for beginners or those without developed white water skills and awareness.