In response to critical water supply issues, the New South Wales (NSW) and federal governments announced a fast-tracked portfolio of drought relief and water security projects. Included in these projects is the proposed Mole River Dam, located in the Border Rivers region of northern NSW. The proposed dam site is situated on the Mole River, approximately 25km south-west of Tenterfield.  WaterNSW engaged SMEC Australia Pty Ltd (SMEC) to deliver a concept design for the Mole River Dam project to meet WaterNSW key project objectives, which were providing water security and improved environmental flows in the river system.  SMEC engaged Geological Consulting to assist with the dam geology, to support concept design development.

The concept design comprises:

• An approximately 70m high clay core rockfill dam, with a 440 m long crest length.
• A spillway located on the left abutment of the dam, comprising an approach channel, crest (control) structure, a chute, and a dissipator.  The spillway requires excavation of around 5 million cubic metres, with maximum excavation depths of around 75m.
• Diversion works, including upstream and downstream cofferdams, and a 10 m external diameter diversion tunnel of approximately 500m length.
• Outlet works including an approximately 60 m high intake tower, conduits passing through the diversion tunnel, and valve house.

Geological Consulting provided technical advice during the site investigations, developed the geological model for the site and characterised the dam foundation and potential construction materials.  Other tasks included providing geological assumptions for a high-level concept development of a Roller Compacted Concrete (RCC) alternative, Potential Failure Mode (PFM) assessment and investigation reporting.