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Options for managing Piha flood risk

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About the options for managing Piha flood risk

The Piha Stream, which runs along Glenesk Road in Piha, is subject to flash flooding. 

The location of buildings, bridges, and roads in the floodplain means that there is a high safety risk in some areas.

In February and April 2018, high levels of rainfall led to significant flooding, which resulted in emergency evacuations on Glenesk, Seaview, and Beach Valley roads. 

After these events, we undertook flood modelling to better understand the risks and impacts of flooding along Glenesk Road.

We have come up with a list of options to address and manage the risk of flooding in the area.

Read detailed explanations of each of the options on the consultation documents page

Options for managing flood risks

Option one: local responses to minimise the impact of storm events (status quo)

We will continue to improve the ways we already respond to flooding in Piha. This includes installing new equipment and signage, and planning Piha-wide emergency management. 

Option two: increase flood warning time

This option would involve installing an enhanced warning system that uses specialist weather forecast modelling and stream monitoring, rather than just rainfall.

Option three: enhance ways of warning people about floods

This option would look to boost cell phone coverage in Piha, in order to increase the effectiveness of our warning services. 

We would also introduce a recorded voice warning system as a part of this option.

Option four: raise Glenesk Road

This option would mean raising the height of Glenesk Road by approximately one metre, which would allow the road to be used for evacuation and for emergency services during a flood event. 

This would involve replacing culverts and a bridge, and upgrading around 30 driveways. It would also involve building new vehicle bays to prevent vehicles from floating away in a flood. 

Option five: build a dam to contain floodwater

This option would involve major engineering works to build a dam to store floodwaters and reduce peak flows during heavy rain. 

There are four options: 

  • Single dam: Piha tributary
  • Single dam: Glenesk tributary
  • Two dams: one on each tributary
  • Single dam: where the Glenesk and Piha tributaries meet.

Option six: build a tunnel to divert floodwater

This option involves constructing a tunnel to divert flood waters away from Piha Stream.

The tunnel would be 1.4km long, four to five metres wide, and would stretch from Piha Stream to Whekatahi Creek. 

Option seven: widen the stream to increase water flow

This option would mean widening and lowering Piha Stream in order to allow floodwaters to drain quickly into the sea. 

We have looked at two options:

  • to manage frequent smaller floods (two-year storm events)
  • to manage larger, less frequent floods (ten-year storm events). 

Option eight: dredge the stream from Seaview Road Bridge to increase water flows

This option involves making Piha Stream larger and deeper from the Seaview Road Bridge.

It would also involve removing the sandbar and sediment build-up in the lagoon. 

The stream would need ongoing excavation and dredging to be effective. 

When you can have your say

You can have your say from 29 March to 30 April 2019.

You can provide your feedback using the online form, by email, or at the public meeting on Sunday 14 April. See the Ways to have your say page for more details