Finding soft alluvial soil under one end of a future cycleway bridge is delaying the start of its construction, Whanganui District Council senior roading engineer Rui Leitao says.
A foot and cycle bridge is to be built, linking Upokongaro to Papaiti Rd. It will fill in a "missing link" of the Mountains to Sea/Ngā Ara Tuhono cycleway.
That section of the cycleway has been closed since 2015, because biking on SH4 is too dangerous.
After crossing the Whanganui River south of Upokongaro the cycleway will instead head to the Whanganui town limit along a new path on the riverbank, joining Somme Pde near Flemington Rd.
The whole project is to cost $2.5 million, with $600,000 from Whanganui ratepayers. Emmetts Civil Construction was to have started bridge construction in May, but a rethink is needed because ground on the Papaiti side is softer than expected.
"During the geotechnical process, Emmetts Civil Construction investigated the ground conditions and determined additional work is required to strengthen the design," Leitao said.
Engineers may need to change the materials used, the pile depth and the bank stabilisation. The bridge is being redesigned by Emmetts with the help of Holmes Consulting, and is now not due to be finished until April next year.
Emmetts is also to build the cycle path to the town limit, with earthwork done by B Bullock. That's to start in September, Leitao said.
The path will run close to Papaiti Rd, along the riverbank, and no other bridges will be needed.
Whanganui & Partners destination marketing strategic lead Paul Chaplow said the bridge will grow Whanganui's cycling culture.
"The bridge will be a real asset to Whanganui, not only because it improves the Mountains to Sea cycle route but because it creates more cycling options with an easily accessible, flat, cycle-friendly day ride to Upokongaro."