The route down from Hinerua to Smiths Stream is badly shown on maps, and is a route, not a track.
From Hinerua Hut, head west along the track towards the tops for 100m to a signposted track junction - the turnoff the Smiths Stream Hut. Here a track drops north, sidles round the top of a slip on the eastern valleyside, and then descends steeply to the stream on short grass / loose dirt of an old slip. By this time the track is a poorly marked route. Once in the stream, the route follows the stream down, with occasional marked detours round tricky sections. The route reaches Smiths Stream at the forks shown.
Smiths Stream is knee deep in normal flows, but would be difficult after rain. Steep valleysides mean that sidling to avoid a crossing is not an option.
From here, head up Smiths Stream in the riverbed. The banks are solid scrub, and the riverbed is on large rounded stones - so it is slow going. Pass the forks below Smiths Stream Hut, taking the western fork. 100m beyond, grassy flats finally open on the northern bank. Exit the riverbed here onto these flats, and nose around for the marked DOC track climbing the face behind. Smiths Stream hut is 20m above the river on a small terrace.