The Bay: Episode 2

May 11th, 2005, 7:30 PM, RTÉ One

Holding Back the Tide

Episode Two tracks recent efforts to improve water quality in Dublin Bay, examining the contribution of the new waste treatment works in Ringsend and the impact it has had on ordinary Dubliners as they swim and dive in the Bay. The programme also looks at the development of the south and north walls, and "the greatest accident that ever happened in Dublin" - the Bull Island.

Further information:

Dublin owes a lot to the bay, but Dubliners have returned much more than the favour. As the population of Dublin doubled over the last 40 years, the dumping of raw sewage into the bay threatened to overwhelm it. In effect, Dublin Bay was drowning in filth.

There was a primary sewage treatment works in Ringsend, which catered for about two thirds of the greater Dublin area. It removed about 40% of the pollution from the waste water directed through the plant, but allowed the other 60% straight through the plant - and on into Dublin bay. The 40%, which was called sludge, was taken out in a sludge ship, the Sir Joseph Bazalgette, which sailed from Dublin port three times a week and dumped the sludge further out beyond the bay. So in effect up until a couple of years ago, all of the waste water from Dublin ended up either in Dublin bay or just beyond it in the Irish sea.

In 1999, Dublin stopped dumping waste on its doorstep. Dublin city council decided to build a single treatment works for the entire Dublin area, so as well as building a waste water treatment works at Ringsend, it also built a pumping station in Sutton, which now pumps all of the waste water from the north Dublin area, and a massive submarine pipeline, 11.5kms long, connecting Sutton to the plant at Ringsend.

The Ringsend works is a tertiary treatment centre, ensuring that all water is filtered, aerated and exposed to UV light before entering the bay. Instead of dumping sludge at sea, the plant is now producing a granular fertilizer. The main effect of all of this is that Dublin Bay is clean for the first time in a couple of hundred years, and as project engineer Battie White puts it, "it means that the people of Dublin can use the bay in full confidence that they're dealing with clean water". Not all Dubliners are delighted with the results, however. Continuing problems with smells from the new treatment plant have left local residents holding their noses.

If you could create Dublin Bay all over again, you wouldn't make it like this. For the entrance to a busy port, it's far too shallow. Big ships need deep water, and Dublin has always had precious little of it.

So the city set out to adapt the bay to its own ends. Almost three centuries ago, the project to control the bay's shifting sands began - and the results have marked it ever since.

Just beyond this the Ringsend treatment plant is the Great South Wall, a spectacular structure stretching out into the bay but which goes almost unnoticed by the majority of the city's population.

The wall was an ambitious - and daring - project. From the harbour at Ringsend, a sea wall - the world's longest at the time - was built. The idea was to narrow the flow of the Liffey, thereby concentrating its power, and prevent sand from the south side beaches from clogging up the port shipping channel.

But impressive as it is, the great south wall didn't clear the sand from the mouth of the Liffey. Enter Captain William Bligh, famous for being thrown off his ship The HMS Bounty in the south Pacific. In 1800... 13 years after the mutiny... he was sent to Dublin to conduct the first detailed survey of the bay, and to suggest ways of improving it. Bligh believed that the south wall was only part of the solution.

He proposed building a second wall from the northern shore, in an effort to further concentrate the flow of the Liffey. Squeezing out between the two walls, the river would dig into the bed and cast the sand and mud out into the bay. The construction of the Bull Wall began in 1819 and was completed in five years.

The north bull wall, and the tidal scour that it produced, was a remarkable success. The force of the water pulled the mud out into the bay from the river's mouth, increasing the depth at low water from 6 to 16 feet. Finally, ships could get into the port at all stages of the tide.

But the North Bull Wall would do far more than open up the port. In the greatest accident that ever happened in Dublin, Bligh's wall created an island behind it - the Bull Island. The steady stream of mud and sand carried by the Liffey waters - which previously had moved out into the bay - was now deposited on the bay's northern shores, just behind the North Bull Wall. And so grew the Bull Island, which now measures 300 hectares and continues to grow.

The island is designated a UN biosphere reserve, and a steady stream of students are attracted to it each year to examine its plant life. The island so accidentally created by Captain Bligh is an internationally important bird habitat. The main attractions are the Brent Geese, which come in large numbers to spend winter here.

But it's not just the wildlife that fascinates on Bull Island. There are two 18-hole golf courses here too, along with a row of cottages that house Dublin's only islanders, and the beach where half of the city has learned to drive - Dollymount.

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