Structural Assessment of Integrity of Rangitaiki River Stopbanks

Draft Job brief

Introduction

This brief is written in response to some stopbank seepage and slight heaving that occurred during the flood of 11-14 July 1998. The intent is to get a quick understanding of the risks (if any) of stopbank failure and interpretation of various warning indicators. Ultimately design solutions may be requested, although this does not limit providing design advice on fast temporary solutions.

Principal

Environment BOP

Consultant

OPUS International Consultants Ltd

Required Outputs

Part I:

A broadscale assessment of identified seepage areas – in particular the two areas where some temporary toe loading is being constructed. These areas are:

 Miro Street (toe-loading largely complete)  Hydro Road at Transpower facility (toe loading underway)  Hydro Road at rail underpass  Anchor Products (two or three areas)  Ngaio Place  College Road (various seeps plus two flood-walls)  Other identified

Provide advice on what the various warning indicators are likely to mean in terms of both imminent (minutes) and longer-term (hours) stability. This advice must be in a format that field staff can readily understand.

Part II

Provide an in-depth stability assessment with factors of safety for the following identified potentially weak areas:

 Miro Street  Hydro Road at Transpower facility  Anchor Products ??  Ngaio Place  Other(s) identified in Part I

This assessment is to include soils testing of stopbank and subsoils, seepage analysis and slope stability analysis. This will include calculating factors of safety under the following two design cases:

Case A: Water level at stopbank crest level.

Case B: Water level 0.25 metres below stopbank crest level (representing water level at half freeboard level).

Payment

Part I: Fees and Disbursements Part II: Requires a detailed estimate of costs

Client Inputs

Previous reports on stopbank design for Rangitaiki and Tarawera Rivers. (To be identified in final brief )

Peter Blackwood Manager technical Services