3/13. Severn Estuary to Aberystwyth. For thousands of years, the world's second greatest tidal range has had a huge impact on the inhabitants of the South Wales coast. Neil Oliver uncovers reaHife horror at the Smalls Lighthouse, Mark Horton explores the terrifying power of sand, Alice Roberts seeks out our Ice Age ancestor and Miranda Krestovnikoff reveals the secrets of rockpools. Plus a chance to witness a dramatic natural spectacle: the Severn Bore. INTERACTIVE: for details see Sunday at 9pm