Pinehaven Stream Improvements

Phase 1 works are expected to be completed in October 2023.

Phase 2 stream improvements will begin 25 August 2023 in the Willow Park area immediately downstream of the Phase 1 works and will include:

• Widening the section of the stream through Willow Park from Sunbrae Drive to Blue Mountains Road.
• Building new retaining walls immediately downstream of the Sunbrae culvert.
• Widening the stream banks (without retaining walls) further downstream, where there is more space available.
• Removing the existing pedestrian bridge over Pinehaven Stream at Willow Park and replacing it with a new pedestrian and cycle bridge linking to 4 Sunbrae Drive.
• Improving the pedestrian path through Willow Park.
• New and replacement planting of native trees and plants.

Works will take around 12 months to complete, with hours of work generally 7am to 5pm Monday to Saturday. No works are scheduled for public holidays.

The project works will be focused on key flooding areas around Blue Mountains Road, Sunbrae Drive, Whitemans Road, Pinehaven Road, Birch Grove, Pinehaven Reserve, and Chichester Drive, Upper Hutt.

By making the stream wider and deeper, the goal is to provide capacity in the stream for a 1 in 25-year return period flood event. So, property owners can expect the capacity of the stream to be five times greater than now.

Pinehaven has a long history of regular flooding events, with 1976 being the largest; Whitemans Road bore the brunt of the floodwaters.

The following year, GWRC and UHCC agreed to jointly administer the Pinehaven Stream with the Watercourses Agreement. However, it became apparent that the flooding issues were closely integrated with the piped stormwater reticulation system. The catchment is also quite contained in nature, within a built environment.

GWRC expressed a desire to transfer responsibility for the Pinehaven Stream to UHCC. The trouble was that the District Plan objectives, policies and rules did not recognise the identified Flood Hazard Extent and associated risk to development for either the Mangaroa River or the Pinehaven Stream. Quite clearly, there was a need to sort out structures that were impeding the flow of water during heavy rain events and improve the capacity of the Pinehaven Stream.

In 2012, GWRC and UHCC worked towards this with Plan Change 15 – Mangaroa River Flood Hazard Assessment. But, there was some discomfort with the flooding modelling results and Plan Change 15 expired over an extended review period. Next, with the Pinehaven Floodplain Management Plan (PFMP) in hand, both councils committed to Plan Change 42 and splitting the Pinehaven Stream Structural Improvements project cost 50/50.

On 27 March 2018, the Upper Hutt City Council (UHCC) unanimously approved Plan Change 42 (PC42). This moment was the culmination of decades of work by Greater Wellington Regional Council (GWRC) and UHCC to address the vexing issue of flood management for Pinehaven community. Two appeals were then lodged with the Environment Court; one relating to matters not affecting the project and the second by Save Our Hills – appealing the entirety of PC42. Experts’ conferencing was completed on 8 April and 9 April 2019. At the May mediation session, Save Our Hills advised that they had withdrawn their appeal. Other parties who joined the appeal continue to work with GWRC. 

Phase 2 stream improvements, funded for $5 million, will begin in July/August 2023 in the Willow Park area immediately downstream of the Phase 1 works and will include:

• Widening the section of stream through Willow Park from Sunbrae Drive to Blue Mountains Road.
• Building new retaining walls immediately downstream of the Sunbrae culvert.
• Widening the stream banks (without retaining walls) further downstream, where there is more space available.
• Removing the existing pedestrian bridge over Pinehaven Stream at Willow Park and replacing it with a new pedestrian and cycle bridge linking to 4 Sunbrae Drive.
• Improving the pedestrian path through Willow Park.
• New and replacement planting of native trees and plants.
• Upgrading the junction where Pinehaven Stream joins Hulls Creek (by the Silverstream Railway Station) to make it easier for fish and eels to travel between the two watercourses

915 metres of channel	14 domestic bridges, 2 road bridges	321 metres of retaining wall	Reinstatement of landscaping in approximately 41 private properties

There will be significant improvements in flood protection for over 50 vulnerable properties and improvements for 179 properties affected by secondary stormwater flow paths. To achieve this, the open channel will need to be widened and deepened, there will be some roading changes, new retaining structures, new residential access bridges and quite a lot of reinstatement of private property.

Plan Change 42:

Addresses-the risk from flooding within the Mangaroa and Pinehaven stream catchments for the 1:100 year flood event. The proposed provisions seek to avoid development in the high hazard area and avoid and mitigate the risk of flooding in the lower hazard areas. A range of structural and non-structural measures are to be put in place, to reduce flood risk to the community.

Complements- the physical stream improvements works by seeking to reduce stormwater generation and the exposure of third parties to flood risk. It also includes some elements that enable the stream improvement works to be carried out.

Introduces- new objectives, policies, rules and other methods to address flooding risks associated with the Pinehaven Stream and Mangaroa River catchments. These new tools provide for certain developments and activities to be avoided with specified (high-risk) areas, and require mitigation and avoidance within other (lower risk) specified areas.