VIC – Remedial works in Commissioners Creek Dam

Author: Aida Baharestani- North East Water.

North East Water is undertaking remedial works on Commissioners Creek dam in Yackandandah, Victoria.

Commissioners Creek dam is more than 100 years old and historically has supplied water to the Yackandandah Township. The dam was taken out of service several decades ago.

An accumulation of sediment has occurred within the reservoir since original construction. Based on a 2014 survey the storage capacity, before the remedial works commenced, was estimated at 20.5ML.  However, the original capacity would have been significantly greater than that.

Prior to remedial works, the consequence category of the dam was “Significant” and the risk of the dam sat above ANCOLD’s Limit of Tolerability.

The main contributors to this risk were insufficient spillway capacity and embankment instability.

The remedial works include lowering the spillway, lowering the water level and reducing the reservoir surface area. The alterations will reduce the consequence category from “Significant” to “Low” and also reduce the risk to an acceptable level. The excess material from excavation is being used to stabilise the embankment.

Figure 1- Commissioners Creek dam- Embankment

Figure 1- Commissioners Creek dam- Embankment

Figure 2- Original Spillway structure

Figure 2- Original Spillway structure

Figure 3- Spillway Channel

Figure 3- Spillway Channel

Figure 4- Post construction Spillway structure and channel

Figure 4- Post construction Spillway structure and channel

Following completion of the concept design, North East Water’s community engagement group consulted with neighbours and the Yackandandah community.

Detail design was undertaken to achieve the following:

  • Maintain the existing dam crest level;
  • Lower the FSL by 2.4m through:
  • Excavating the accumulated sediment and dense vegetation in the approach area;
  • Demolishing the existing concrete crest structure;
  • Excavating the initial portion of the spillway channel ;
  • Construct a new spillway crest sill and upstream apron with anchored, reinforced concrete slabs;
  • Construct a stability berm using the excavated material from the spillway works.

North East Water met with the residents to discuss any concerns and the plans for the Dam and subsequently hosted a Community Workshop on the future opportunities (including ownership) of the dam. It was determined at this meeting that North East Water would, on behalf of the community, investigate the various opportunities for community ownership of the dam, after the dam works are completed, and report back to the community.

The construction works commenced in the first week of February 2016 and were completed by the end of the month.