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Waiomu Flood Protection Interim Report

Report: TR 2006/26
Author: Ghassan Basheer

Abstract

Following the severe floods generated by the “weather bomb 2002” on the Thames coast, Environment Waikato and Thames Coromandel District Council have jointly worked to address the flooding issues along the Thames Coast. The work included risk assessment, technical investigations, a business case to Central Government, community consultation and establishment of a funding system to provide for undertaking flood mitigation works.

Waiomu is one of the five priority communities identified as having a very high risk to life and property, requiring actions that address these risks.  A critical area of risk within the Waiomu community is the Waiomu Bay Holiday Park.

The initial investigations into the flooding of the Waiomu settlement is set out in Environment Waikato Technical Report 2003/10 dated 13 August 2003, and community meetings, identified the issues causing and exacerbating flood risks and proposed solutions for these. The issues included:

  • catchment stability
  • lack of channel maintenance
  • inappropriate development within the floodplain
  • State Highway 25 and the bridge waterway capacity
  • local drainage network.

In addressing these issues both councils have jointly adopted a whole catchment approach and strategically engaged with central government to ensure that the issues are addressed sustainably in the long term. The main tasks undertaken following the initial technical investigations included the following:

  • risk assessment
  • business case to central government
  • community consultation.

The Peninsula Project was initiated in 2002 and formally adopted in 2004 to address river and catchment issues across the Coromandel Peninsula. This umbrella project identified the river and catchment services needs over the whole peninsula area, established a long term works programme to meet these needs and a funding system that supports implementation of these programmes and maintaining their benefits in the long term. The programme within the Waiomu catchment included the following:

  • establishment of the channel maintenance programme
  • establishment of a catchment management programme including soil conservation and animal pest control in conjunction with the Department of Conservation
  • establishment of the flood protection and channel improvements capital works programme.

The success of the business case provided different levels of central government contributions to implement the proposed capital works programmes. However, upgrading the State Highway 25 bridge could not be included in the Transit NZ 10-year plan. This meant that a staged approach needed to be taken in providing flood protection within the Waiomu community.

Since July 2004, detailed surveys and conceptual design reviews have been undertaken to ensure that flood risks are addressed sustainably in the long term. The results of the review provided that the initial conceptual design didn’t provide adequate floodway to accommodate current and future flood flows. A significant part of the campground area needed to be retired as a floodway. Negotiations with the landowners were concluded with the purchase of the whole campground and No. 2 Waiomu Valley Road properties.

This report provides the results of the design review, the proposed flood protection and control works and future management strategy to ensure that flood risks within the Waiomu community are addressed in a sustainable manner.

Waiomu Flood Protection Interim Report
(979 kb, 139 seconds to download, 56k modem)

Table of contents

Introduction  1
2 Conceptual design review  2
2.1 Background  2
2.2 Scope of hazards  2
2.3 Original design  3
2.4 New design concept  5
3 Design parameters 10
3.1 Floodway parameters 12
3.2 Remainder of campground 12
3.3 Right bank stopbank 14
3.4 Stream bank stabilisation 15
4 Implementation 15
4.1 Stage I 15
4.2 Stage II 16
5 Planning controls 17
5.1     Greater than design flood events        17
5.2 Debris flood events 17
5.3 Climate change 17