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Piako River Scheme - service level review

TR 2018/06

Report: TR 2018/06

Author: Murray Mulholland

About this report

The Piako River flood protection scheme provides protections to Ngatea and Pipiroa townships, farmland, and several roads of national significance. A key Level of Service of the scheme is that it is designed to control the effect of a flood event, up to a specific size. The objective of this study was to review whether the actual level for all the stopbanks and spillways of the scheme meet the current service levels.

Tidal zone stopbanks
Performance of the Piako River Scheme main tidal zone stopbanks is generally acceptable under the current climate scenario, although 9% (9.7 km) are currently graded as being 4 or 5. These elements require topping up. In general adequate capacity is available for the Awaiti Canal stopbanks to provide protection against a 3m 100 year ARI high tide event with 0.5m freeboard, except for a 0.78 km section on the left bank.

River zone stopbanks
The River Zone stopbanks currently have 1.6 km (16%) graded as being 4 or 5. The Kerepehi Block No 2 Cutoff stopbank is the highest priority as it overtopped during the April 2017 flood event.

In general the ponding zone spillways need to be raised at low points to prevent frequent overtopping. An exercise to prioritise spillway upgrades will be completed to provide a forward works programme.

Read or download the report

Piako River scheme: Service level review [PDF, 3.6 MB]


  Executive summary
1 Introduction
2 Scope of Scheme Review
2.1 Exclusions
3 Drivers for Activities
4 Service Requirements
5 Performance Measures
5.1 Stopbanks
5.2 Spillways
5.3 Performance Expectations
6 Performance Grades
6.1 Stopbanks
6.2 Spillways
7 Service Level Options
7.1 Status Quo
7.2 Ponding Zone Spillways Protected to Full 50 Year ARI Standard
7.3 Climate Change to 2090
8 Performance Assessment
8.1 Hydrological and Hydraulic Assessment
9 Results
9.1 Stopbank and Spillway Level of Service
9.2 Main Tidal Zone Stopbanks
9.3 River Zone Stopbanks
9.4 Scheme Ponding Zones (Spillways)
9.4.1 First Emergency Ponding Zone
9.4.2 Second Emergency Ponding Zone
10 Conclusions