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   …Wivenhoe has a clay core and an earthen wall which is lined on the outside with rocks. Unlike Somerset Dam which has a concrete wall, Wivenhoe has no structure which could withstand the force of water flowing over its wall. If over-topped by flood-water, the Wivenhoe wall would quickly erode and fail, releasing the contents of a full Wivenhoe to flow down the Brisbane River at torrential speed…