 ANCOLD lists Trevallyn Dam as having a dam wall height of 33 metres and the total volume of the wall as 61,000 cubic metres.The dam diverts water to the Trevallyn Power Station through a 3.2 km tunnel.Lake Trevallyn is the long, narrow lake created by the dam and extends as far as Hadspen where the first rapids begin at the junction of the Meander and South Esk Rivers.