2011 – Blackman Dam Failure Emergency Management

Ben Hanslow and David Brett

The Blackman Dam is a 27 m high, zoned earthfill dam located upstream of the township of Tunbridge in the Tasmanian Midlands. The dam has an estimated storage capacity of 7300 ML and an assigned Hazard Rating of High C.

The Blackman Dam was constructed over the period November 2003 to September 2004. The dam supplies water for irrigation to farms in the area and potentially to the local towns of Tunbridge and Oatlands.

Filling of the Blackman Dam commenced in 2005. After substantial filling of the dam and following a heavy rain event, an area of seepage was noted on the far left abutment of the main embankment mid morning of Thursday 13th October 2005. The seepage was reported by the dam operators as being “garden hose flow”. By mid afternoon of that day, this had increased to “100 mm pipe flow” and discoloured. The Dam Safety Emergency Plan was activated.

This paper discusses lessons learnt and provides details on the implementation of the Dam Safety Emergency Plan and emergency actions taken to successfully avoid a breach of the dam wall. The paper also provides details on the geotechnical investigations that were carried out and factors contributing to the piping failure. Embankment repairs were successfully completed by mid 2010 and first filling of the Blackman Dam occurred in 2011.