St Helens Major Drainage Upgrade

Client: Break O’Day Council
Location: Cecilia Street, St Helens, Tasmania
Period: Pre-2013 flood response delivery phase
Collective Consulting Services: Superintendent services, contract administration, local engineering support, tender evaluation, stakeholder coordination and construction-phase engineering
Completion: 2014

Project Overview

Following a significant flood event in St Helens that inundated several commercial properties within the central business district, Break O’Day Council initiated a major flood mitigation and drainage infrastructure upgrade for the township.

The flooding particularly impacted low-lying commercial areas near the bayside retail precinct, including the hardware and retail sector, highlighting that the existing drainage infrastructure was inadequate and had evolved over time without an integrated long-term strategy.

Council engaged an interstate flood engineering consultant to undertake a flood study and identify a long-term mitigation solution. The adopted solution involved the construction of a new major drainage spine extending approximately 1.1 kilometres through Cecilia Street, from the southern to northern end of the township.

Drainage Infrastructure Solution

The project involved construction of a major underground drainage network designed to collect and rationalise numerous smaller drainage systems throughout the township into one coordinated flood mitigation system.

The primary infrastructure included:

• Approximately 1.1 km of major drainage infrastructure
• 1400mm x 1400mm precast concrete box culverts through the majority of the alignment
• 900mm diameter pipeline systems through remaining sections
• Major junction pits and property connection points
• Drainage discharge infrastructure to Medeas Cove and the bay system
• New road pavements, kerb and channel and footpaths
• Groundwater and subsoil drainage improvements

The box culvert system was ultimately optimised during the tender and delivery phase using an inverted precast concrete culvert solution with in-situ concrete lids and pavement construction over the top. This methodology improved constructability, accelerated installation and enabled improved management of groundwater and pavement drainage.

Geofabric separation layers and blue metal drainage backfill were incorporated to improve constructability and allow the drainage system to act as both a stormwater network and a long-term subsoil drainage system for surrounding roads and commercial properties.

Stakeholder Coordination and Engineering Challenges

One of the project’s most significant challenges was the interaction between the new drainage infrastructure and existing underground services throughout the township.

The scale and depth of the new culvert system created clashes with:

• TasWater infrastructure
• TasNetworks services
• NBN and communications infrastructure
• Existing property connections
• Legacy and unidentified underground services

Collective acted as the local engineering consultant during delivery and provided rapid-response engineering support whenever unforeseen service conflicts or constructability challenges arose.

Solutions included:

• Service realignments
• Infrastructure deepening and relocation
• Temporary service arrangements
• Integration of existing services within the culvert system where feasible
• Rapid redesigns to avoid construction delays

Collective also assisted Council with stakeholder negotiations and coordination between utility authorities, contractors and local businesses to minimise disruption and maintain project momentum.

Contract Administration and Delivery

Collective undertook:

• Tender evaluation
• Superintendent services
• Contract administration
• Construction-phase engineering support
• Procurement coordination for precast concrete components

Council awarded the construction contract to Shaw Contracting, who developed an outstanding delivery methodology that significantly contributed to the success of the project.

Hudson Civil Products supplied the precast concrete culvert components directly to Council, with procurement coordinated to meet an accelerated winter construction program.