Gregory Highway 27B – LN1 Culverts Upgrade Planning (Business Case)


Department of Transport & Main Roads

Project value





Emerald, Qld



LN1 drain is a main channel within Selma irrigation system which extends from downstream of Fairbairn Dam and along the Western bank of the Nogoa river in the Emerald area. LN1 passes through the north-western section of Emerald and crosses Gregory Highway (Emerald – Clermont) (27B) at Ch 2.16km. LN1 drain also acts as a breakout channel from the Nogoa River during heavy flood events (regional flood events) and acts as open storm water drain for local flood events.

In 2008 and 2010/2011 Emerald experienced severe flooding. Various studies were conducted by the Central Highlands Regional Council (CHRC) to investigate potential options to mitigate flooding impacts, one of the recommendations was to increase the flow capacity in the LN1 drain.

Department Transport & Main Roads (DTMR) is planning to explore the options as listed in Section 4 of the brief and complete a Business Case for proposed upgrades of the culverts, under the provision that CHRC/Sunwater commit to upgrade the LN1 drainage channel downstream of the Gregory Highway crossing to mitigate impacts prior to funding being made available to upgrade the crossing.

Cardno have been engaged by DTMR to prepare a Type 3 business case and have engaged Bellwether to carry out the estimating services required as part of the business case.

Option 1: Add additional cells to the existing culvert structure to achieve the goal of widening the culverts while maintaining the existing road formation. Maintenance of existing road surface level is required.

Option 2: Replace existing culverts with double the number of culverts while maintaining the existing road surface level that is suitable for use by Type 2 Road Trains

What we delivered

Bellwether prepared a P50/P90 cost estimate (total project cost) for the selected option using estimated quantities and historical rates, in accordance with the DTMR current Project Cost Estimating Manual.


The estimates considered the following:

  • Preconstruction cost:
    • Design Development phase, and
    • Detail Design phase
    • Construction phase Costs:
    • Category 3 high level analysis of options estimates
    • Category 4 Concept Estimate of Cost (P50/P90 of selected option)
    • Category 4 Concept Estimate of Cost (P50/P90 of selected option)
    • Basis of Estimate report
    • A Contingencies allowance will be made based on risk analysis calculations.

Key outcomes

Carmichael Coal Mine & Rail Network
DTMR Henri Roberts Drive (in progress)
Blythe River Bridge Strengthening
North Brisbane Bikeway – Chalk Street to Price Street
Captain Cook Highway Smithfield Bypass
Tinaroo Falls Dam Raising
Nullinga Dam Detailed Business Case
Stony Creek & Lindenow Options
Warrego Highway / Mt Crosby Road Interchange Upgrade
Fairbairn Dam
Maturing the Infrastructure Pipeline Program (MIPP)
Land Street Bikeway Underpass Duplication
Morayfield Indoor Sports and Events Centre Expansion
Torbanlea – Pialba Road Floodway Replacements Business Case
Samford Road Options Analysis
Logan Motorway East Bound Drainage Improvements and Pavement Rehabilitation
Gold Coast Tourism Hub Project – Bundall Road Site
Greenbank Transport Corridor
South Burnett Regional Council Systems Review
Cannon Hill Shopping Centre Bus Facility – Bus Station Upgrade
Newell Highway Flood Immunity West Wyalong to Forbes
Mareeba-Dimbulah Road Widening and Roadside Safety Improvements
Calliope River Bridge and Anabranch Bridge: Engineering Analysis and Options Analysis
North Pine Hub Strategic Assessment
Gregory Highway 27B – LN1 Culverts Upgrade Planning (Business Case)
Barwon Heads Road, Black Rock Road and Staceys Road Roundabout
Pacific Highway Upgrade – Woolgoolga to Ballina
Easing Sydney’s Congestion – Pinch Point Program
Burdekin Falls Dam Improvement and Raising
M6 Early Works Construction
Warragamba Dam Expert Witness Report
South Batemans Bay Link Road
Gunns Gully Road Interchange
M1 Princes Motorway Improvements
Circular Quay Precinct Renewal
Wynnum Road Corridor Upgrade
Arrow Energy Dalby – Laydown Yard
MSC Charleville Industrial Estate
BSC Leans Creek Bridge & Richardsons Bridge Repairs
CHRC Springsure Landfill Rehabilitation
CHRC Capella Landfill Rehab & Transfer Station
MRC Whittle Street Drainage Upgrade
TRC South Street & Burton Street Intersection
Seqwater creek & pipe protection works
MRC Warland Street Drainage
MRC Mackay Bus Stop DDA Compliance Program
MRC Juliet Street Pavement Rehabilitation
NDRRA Flood Betterment Works
Retail First Brookside Shopping Centre Embankment Stabilisation & Car park extension
NSC Black Mountain Road Safety Improvements
TRC Toowoomba Waste Transfer Facilities (*3)
Australian Department of Defence – Kokoda Barracks
Australian Department of Defence – Enoggera Barracks
MRC Caping Road Bridge
DTMR Virginia Park ‘n’ Ride Upgrade
BRC Bruce HWY Upgrade & Streetscape, Gin Gin
MRC Milton Street & Archibald Street Intersection Upgrade
WDRC Warrego Highway Upgrade and Streetscape, Miles QLD
MBRC Aurthur Drewett Drive
WDRC Bundi Creek Bridge (in progress)
NSC Noosa Parade Upgrade