mt white rd hawdon river bypass bridge - reaaa
TRANSCRIPT
Mt White Road – Hawdon River
Bypass Bridge
Mark Chamberlain – Selwyn District Council
20191
Mt White Road - Hawdon River Bypass Bridge
Off SH73 approximately 23 km south of Arthur’s Pass.
Bridge crosses Waimakariri River.
Then a ford crosses a low flow braid of the Hawdon River with a bypass bridge when the ford is not able to be crossed.
Those familiar with multisport may be aware that this is the transition from bike to kayak for the Coast to Coast.
Mt White Rd provides access to Mt White Station (25 km from SH73) and DoC walking tracks.
Mt White Rd - Hawdon River Bypass Bridge
A heavy rain event on 8 November 2018 had 330 mm of rain including 110 mm in a four hour period caused a heavy flood down the Hawdon River.
This washed out the upstream Groyne protection and the ford bypass bridge.
The Groyne protection kept the main Hawdon River flow away from the bridge over the Waimakariri.
This has been successful since the late 1980’s when that bridge was upgraded.
Note the well vegetated river bed between the Groyne and ford.
The old timber bypass bridge was in poor condition but served it’s purpose.
Gabion Groyne
and gravel bund
Bypass Bridge
Ford
Mt White Rd - Hawdon River Bypass Bridge
Aerial showing the increased flow path after the Groyne washed out.
Mt White Rd - Hawdon River Bypass Bridge
The result was access restricted to Mt White Station and DoC tracks when river is flowing.
Proposed reinstatement of river controls upstream and replace bridge with concrete box culvert.
Design by HEB through road maintenance contract.
Consultation with DoC, Mt White Station, Ecan and NZTA.
NZTA approved emergency works funding.
Ecan approved the Groyne reinstatement as it is like for like.
Ecan resource consent required for the box culvert replacement of the timber bridge.
Work delayed awaiting consent decision.
Groyne
Bypass Bridge
Ford
Mt White Rd - Hawdon River Bypass Bridge
View from Mt White Rd Bridge over the Waimakariri.
Bridge FordGroyne
Mt White Rd - Hawdon River Bypass Bridge
Flooded ford
12 November 2018
Mt White Rd - Hawdon River Bypass Bridge
Reinstated ford
20 November 2018
Mt White Rd - Hawdon River Bypass Bridge
Flow at the bypass bridge
12 November 2018
Mt White Rd - Hawdon River Bypass Bridge
Damaged bridge
20 November 2018
Mt White Rd - Hawdon River Bypass Bridge
Above Groyne location with flow along east bank.
Bund constructed to redirect the flow and provide protection during Groyne reinstatement.
20 November 2018
Mt White Rd - Hawdon River Bypass Bridge
Looking downstream (from the bund) at Groyne location where the flow followed the east bank.
20 November 2018
Bridge
Mt White Rd - Hawdon River Bypass Bridge
Looking downstream at the Groyne location from further bund formation.
Bund to provide protection for the gabion Groyne construction.
Bridge
Remains of old gabion Groyne
Mt White Rd - Hawdon River Bypass Bridge
Gabion Groyne reinstatement.
Gabion baskets (75m of 2m high, 2m wide, ‘pyramid’ style), and 75m gabion mattresses.
September 2019
Bund material will then moved to cover the Groyne construction.
Mt White Rd - Hawdon River Bypass Bridge
Gabion Groyne reinstatement
September 2019
Mt White Rd - Hawdon River Bypass Bridge
Gabion Groyne reinstatement
September 2019
Mt White Rd - Hawdon River Bypass Bridge
Gabion Groyne reinstatement
September 2019
Mt White Rd - Hawdon River Bypass Bridge
Triple box culvert design
Consent granted by Ecan September 2019
Construction planned for November 2019
Emergency work one year after the rain event!
Mt White Rd - Hawdon River Bypass Bridge
Any questions!