Classic Canterbury braided river, with some nice huts and options for tramping side trips. Easily done as a day trip, you could spend many days exploring the upper catchment before floating back down to your car.
Waimakariri Valley: Carrington Hut Route
The Waimakariri Valley is a major route featuring in a number of classic Arthurs Pass tramping trips. Often it’s the start or end of a more adventurous trip, so often gets unlovlingly refered to as a ‘gravel slog’. However, it does have some nice scenery, as well as being a great starting point for lots of adventures.
The Carrington Hut Route guide on the DOC website has excellent information about access options in the valley.
Essentially, when the river is low, you hike up the river bed, when high, you use the sidle track. About 4hrs from the road to Carrington Hut (36 bunks).
Waimakariri River (I-II) from Carrington Hut to Klondyke Corner
The ‘Waimak’ is a classic braided river: Some slightly harder class II rapids up higher (near Carrington hut), followed by multiple braids. You’ll need to pick your braid carefully to avoid having to walk the shallow sections.
Waimakariri River at Esk.
Needs a bit of water to make it floatable. 0.5m would be the bare minimum, otherwise you’d be walking more than floating. Even at 0.6m, Sam Newton reported several portages due to too little water.