The Ngaruroa River is large and travel in the riverbed is likely to be realistic only in low flows. A route leads upriver to Omarukokere Biv, and can be traveled almost entirely on the valleysides - but at least 1 crossing will be required, and 5 crossings are preferred. If the river is not crossable at Rocks Ahead, it will probably be impassible at Omarukokere too.
From Rocks Ahead Hut, head up the track towards Venison Tops on the eastern (true right) valleyside. About 50m above the river the steepness of the slope lessens and good deer trails (2014) lead along the valleyside upriver. These can be followed 1.5km to the first major bend where it is necessary to drop to the valley floor to cross the sidestream. It is possible to remain on the eastern bank round this bend, but a slip means that a a climb/scramble is required. If the river is low, 2 crossings avoid this.
The riverbed becomes broad shingle, and travel on the valleyfloor is possible for much of the remainder of the trip, with bush-bashing on banks required in places. Good crossings to the western bank exist at the biv, or 300m downriver at the downriver side of the 1st major bend. If on the western bank, a tape-marked side is necessary to avoid bluffs and marsh just below the hut.
Note: Described in the reverse direction to your journey
From Omarukokere Biv, travel downriver to Rocks Ahead is via an unmarked river route. Travel in the riverbed is likely to be possible only in low flows. Travel on the valleyside is possible if the river is high - but at least 1 crossing is required to the eastern bank (the western bank is impassible due to slips near Rocks Ahead). If the river is too high, the alternative route up the spur west of the bivvy should be considered.
The best crossings to the eastern bank are at the bivvy, or 300m downriver at the first bend., If these are nit possible then this route should not be attempted. For the first 2km of winding valley, there are frequent shingle flats, and travel on the valleyfloor is often possible with brief bush-bashes (on the eastern valleyside) necessary where the valley tightens. Downriver of the last bend (at pt773) a slip cuts the eastern valleyside upriver of the sidestream, and 2 crossings are preferred to bypass it. Alternatively a scramble could get over it if the river is up.
Downstream of the confluence at pt773, the eastern valleyside is normally the only option (the western face is steep and cut by slips). Though the face is steep and tangle, reasonable deer trails and gentler slopes exists 20m-50m above the river, and make for slow but 'doable' travel downstream. The Rocks Ahead - Venison Tops track cuts down the spur and by sidling you will eventually hit this track which you can follow to Rocks Ahead Hut.
The sidestream above the hut is bridged.