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The bike park committee held a soft opening for the Achil St loops in March, but saved the official event for when the Olympic silver medallist could attend.
President Pierre Leyser said it was "absolutely fantastic" Walker had agreed to open the park.
"The committee has been working hard to get her here."
It was "touch and go" whether she would be able to ride on the day because of a shoulder injury she received in May, he said.
There will be children’s bike races and a jump park demonstration from 10.30am to noon, followed by an unofficial BMX meet.
The park has five different loops of varying difficulties, from a paved learn-to-ride area with street signs and intersections up to a jump loop.
The opening would be "low key", Mr Leyser said.
The bike park was well-used, even by adults, he said.
"It’s the kind of track where you can really learn how to ride.
"It’s getting even more use now with daylight saving."
Since the soft opening in March, the committee has planted grass and installed two retaining walls and a picnic table.
The park was built using $400,000 from grants and fundraising.
Some labour and equipment was donated by the firstname.lastname@example.org