http://pandora.nla.gov.au/pan/96122/20090317-1643/www.bom.gov.au/lam/climate/levelthree/c20thc/flood3.html Northern Tasmania, April 1929] After rainfall of 125 mm in ninety minutes, the Briseis Dam gave way upstream of Derby, causing a torrent of water to rush down the narrow gorge of the Cascade River.