Geoff Helisma, Clarence Valley Independent
The cost of vital repairs to the rock gabion dam at the foot of the Shannon Creek Dam spillway has blown out from the awarded $1.145 million (ex GST) contract to a “foreshadowed variation” budget of “between $3.16 million and $4.13 million”.
At yesterday’s February 23 Clarence Valley Council (CVC) meeting, staff recommended that councillors “note” the variation, “due to adverse ground conditions”, and include “the final variation … in the [third quarter] budget adjustment”.
In July 2021, councillors awarded the $1.145 million contract, to repair “significant damage to an existing rock gabion structure, following a one per cent average exceedance probability (AEP) flood event in December 2018”.
However, at yesterday’s meeting it was revealed, “additional geotechnical investigation, undertaken by the contractor during the design phase of the contract, has shown that site subsurface conditions are significantly poorer than the information provided in the tender background information, and [that] the foundation options proposed in the tender will therefore not meet the specified design requirements”.
CVC’s dam safety consultant concurs, the report stated, and “the contractor has foreshadowed a variation to construct a foundation which addresses the subsurface conditions”.
Staff advised that the initial contract “only authorised variations [of] up to 15 per cent … [and that] the foreshadowed variation is reported to council for noting”.
Staff have taken the unusual step of seeking a “foreshadowed variation”, because a delay in adopting “a formal price variation” is likely to incur extra costs.
“The contractor has advised that the variation needs to be approved within five working days to avoid delay costs, and it is expected the variation will be received in the week commencing 28 February 2022,” the report to council stated.
“If the variation were reported to council after receipt, it is anticipated that there would be at least two weeks of delay costs, as a result of the CVC meeting cycle.
“Detailed design is currently being finalised and council’s dam safety consultant (Public Works Advisory) will need to concur with the preferred option.
“When concurrence to the detailed design is received, the contractor will be in a position to provide a formal price variation, which they estimate will take about one week to prepare.
“The remediation to the tailwater dam is necessary to avoid erosion of the creek downstream of the spillway.”
Coffs Harbour City Council (CHCC) will contribute 44 per cent of the cost of the remediation, as a result of the recent water supply agreement between the adjacent local governments. “Were the design as per the original tender [was] constructed, it is likely that it would fail in the future, due to the subsurface conditions,” staff advised.
This article appeared in the Clarence Valley Independent, 23 February 2022.
