Nick Crane explores the wealth of wildlife and industry that are attracted to
the Firth of Forth, the mighty estuary that feeds Edinburgh. To reveal the
secrets that made this coastline famous for salt production Nick must answer a
deceptively tricky question that intrigues children and baffles adults: Why is
the sea salty? Nick also investigates a remarkable natural phenomenon
discovered accidentally on this coast in 1834. First seen in the water of a
canal near Edinburgh and dubbed the 'Soliton', it's a rare type of wave that
appears to travel endlessly, without losing energy and without breaking up,
even when it collides with another Soliton wave. Now engineers have created
tiny Soliton light waves, which could revolutionise the next generation of
fibre-optic communication by transmitting messages effortlessly between
continents.

Miranda Krestovnikoff witnesses the extraordinary transformation that salmon
must make to their bodies to avoid death by dehydration as they migrate from
freshwater to saltwater. This complex lifecycle made farming salmon practically
impossible. So how, in 1971, did Scottish fish farmers discover the secret of
managing salmon in captivity? Scotland's pioneering efforts created a business
worth around half a billion pounds a year, making the noble salmon Britain's
favourite fish dish.

It's a dirty job, but someone's got to do it; Tessa Dunlop reveals how the
Victorian zeal for cleanliness turned the Thames into a giant self-flushing
toilet bowl. It was an ingenious system that relied on the power of the tide to
wash the capital's sewage out to sea, a visionary scheme that ended in triumph
- and tragedy. The sewage tunnels themselves are still used, but in 1878 the
tragic deaths of 600 day-trippers aboard the SS Princess Alice, a pleasure ship
wrecked in the Thames, caused such outrage that London's twice-daily tidal
flush was abandoned. The unfortunate victims had plunged into a toxic soup of
raw sewage, where they perished. London's mighty 'Tidal Flush' was replaced by
a fleet of purpose-built ships, carrying human waste from the capital out to
the North Sea. Known to locals as 'the Bovril boats' these unsung heroes
continued with their vital daily task right up until 1998.

Mark Horton discovers the astonishing struggle to build a rail tunnel deep
under the Severn estuary between England and Wales, a challenge that was
finally accomplished in 1886. Commuters on the 450 trains that now use it each
day are unaware that a vast spring of underground water still pours
continuously into the tunnel. Construction was halted for years as Victorian
engineers tried to stem the underground spring, but they failed. Even today the
rail link is only kept dry by powerful pumps that stop the rising waters.

And multi-award winning folk-singer, June Tabor, returns to Coast to conjure up
the haunting 'Brean Lament'. June explores the superstitions surrounding the
burial of shipwrecked sailors at the Somerset village of Brean, sited at the
mouth of the mighty River Severn - where rivers and seas collide.