Department of Transport & Main Roads
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
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: