They're made of solid oak, weigh almost 4-tonnes, and can withstand the pressure of thousands of gallons of water for up to 30-years. But this winter, a set of lock gates on the Kennet and Avon canal in Berkshire are getting some much needed repairs. And there's an extra challenge - the gates need to be physically lifted out of the canal. As David Allard reports, it's a project which balances careful conservation with the forces of nature. | BBC Hampshire & Isle of Wight