Design and Performance of a 'Flow - Through' Spillway at Broderick Creek Waste Rock Dump - Savage River Mine

Australian Bulk Mineral's Savage River iron ore mine is located in rugged topography in the NW of Tasmania, a region with rainfall in excess of 2000mm per annum. Over its 30 years of operation to date, around 260 million m3 of waste rock has been generated and current mining plans allow potential for a further 160 million m3 over the next 20 years. Disposal of this material poses significant difficulties, not least of which is the practical placement of such large volumes of material. Erosion of early dumps placed in Broderick Creek was recognised as an environmental issue and led to a review of spillway options for the dump, which was effectively damming the valley. Lying parallel to and to the west of the northern deposits of the mine, Broderick Creek was a logical waste rock disposal site if stormwater flow could be properly managed. The review led to adoption of an innovative flow-through spillway, which utilised hard coarse waste rock as a drainage zone. Construction was successful and has led to extension of this concept for further major development of waste dumps at the site. Design of flow-through spillways in Tasmania was first looked at by the eminent Hydro Electric Commission engineer, the late John Wilkins. Wilkins used the concept successfully at Laughing Jack Dam and later at the North Slot Dam at Savage River. The paper describes the work of Wilkins and how this was used to design the Broderick Creek structure. Results of site flow monitoring are used to demonstrate the effectiveness of the design and actual permeability values achieved.