Cotter Dam Enlargement

The enlargement of Cotter Dam provides water security for Canberra.

Client: ACT Energy and Water

Services: Initially engaged during the development phase to provide cost and constructability advice for business case planning. Subsequently Project Support undertook independent estimates to support the Alliance Target Cost Estimate. we provided the following services;

  • Cost and constructability advice for business case planning.
  • Independent Estimator for Alliance
  • Construction phase project ‘Health’ checks over 4 years

Project Cost: $400 M

Time frame: 2009 – 2013


Water security for Canberra’s growing population during periods of droughts needed to be secured.  The enlarged Cotter Dam provides that security. It is a roller compacted concrete dam with a concrete spillway face built to replace the existing smaller Cotter Dam. The project was delivered through an Alliance and sourced over 1,000,000m3 of rock for crushing to produce aggregates, and sands for the 380,000m3 of RCC used in the wall. The expanded capacity went from 4 Gigaltires to approximately 78 Gigalitres. Total construction costs were in the order of $400M.


As ACT Energy and Water’s Independent Advisor we worked with Abigroup – John Holland joint venture and the engineering design team at GHD to add value, identify cost savings and mitigate risks.

Our role continued during the construction phase to verify any variation in costs and to provide interim project ‘Health” checks over a four year period.


The project was completed in 2013 with and excellent quality and safety record. The project won and Engineering Excellence Award (2013) ensuring our client got value for money achieved their project goals.