DEPARTMENT of Conservation (DOC) staff have assessed two hut sites on the western side of the Egmont National Park after rivers changed their course and banks collapsed during recent storms.
A long-standing hunter's bivvy near the Taungatara Track was left perched on the edge of an island after flood waters rushed
past the hut on each side The bivvy was, solid but the stream was too close for comfort and the hut was airlifted out last week.
The popular Waiaua Gorge Hut is another under scrutiny. It was built in 1984 after flood danger saw the Oaonui Hut dismantled.
"We built a new hut well away from the stream," said Dave Rogers, DOC Taranaki's asset manager. "But in 1998 the stream followed us to the new site."
That year a massive lahar saw the Oaonui stream jump into a dry river bed and cut its own course to a depth of one metre. The stream has stayed there gradually deepening year by year. The original Oaonui Stream took the overflow at times, but after this year's rain, there is a three-metre lip between the two river beds.
"Erosion seems to have accelerated as the river bed has deepened," said Dave.
"The pure volume of water churning through is undermining the bank and walls are collapsing. This creates a dam and when that lets go the real damage is done."
Part of this stream is subject to a geologists report because it runs behind the Waiaua Gorge Hut. The closest point is 75 metres away so the hut is safe, but the geologist's report will help identify just how far the gorge walls are retreating. This helps with risk management decisions and determines whether the hut has five, 10 or 15 more years' life left and whether to rebuild on a new site.
Six to eight metres of rain falls in this spot over a year. "That's a lot of rain," said Dave. "But it's not unusual. Big changes seem to have happened every five years, but perhaps they are happening more frequently. It pays to watch these things closely."
