What makes Dublin Bay so murky?

 

Sir, – Further to Peadar Farrell’s letter (May 8th) regarding dumping of dredging spoil on the Burford Bank and the rebuttal by Eamonn O’Reilly of the Dublin Port Company (May10th), I wish to state some pertinent facts.

Mr O’Reilly states that dredging has been a feature in Dublin Port since the early 20th century. This is so, but much dumping of obnoxious waste has also been taking place in Dublin Bay during the same period.

From 1877, the Rathmines and Pembroke sewer was discharging raw sewage into the Liffey, and hence to Dublin Bay, at the outfall on the South wall. The completion of the greater Dublin main drainage system in 1906 brought much of Dublin’s sewage to new settling pans that had been built in the old Pigeonhouse Harbour at Ringsend. This gave a rudimentary treatment to the sewage with the overflow passing directly to the Liffey.

The remaining sludge from the settling pans was put into specially built vessels, which included two named ‘Shamrock’, and the ‘Sir Joseph Bazalgette’. The site where this material was dumped by these vessels was just off the Bailey Lighthouse at Howth Head, technically just outside Dublin Bay, which was defined as being inside a line drawn from the Bailey to Sorrento Point at Killiney.

During an underwater survey that was carried out by myself and some diving colleagues of the wreck of the paddle steamer Queen Victoria near the Bailey some years ago, we had just finished diving when the Sir Joseph Bazalgette arrived on the scene and proceeded to discharge a vile maelstrom of filth into the water before steaming back to port. Until quite recently the sewage of much of North County Dublin was discharged from an outlet on the seaward side of Howth Head. Sewage from the Dún Laoghaire- Rathdown area was discharged from an outlet on the Bay side of the West Pier. These outlets have all been connected to the new sewage works at Ringsend, but all are still capable of being opened whenever heavy rainfall affects the working of the Ringsend plant.

A great many interested parties once made submissions to a survey as to how Dublin Bay and environs could best be managed. One of the suggestions made inter alia by my diving group, and a great many more parties, was that dumping of sewage sludge at the Bailey should cease, and if dumping were to continue, that it should be done outside the Kish Bank in deeper water, where the strong north-south tidal flows would ensure greater dispersal. Thankfully this suggestion was acted upon, and it might well serve as a model for today’s dumping.

Until recently, there was much comment and debate about what caused the dreadful stench that emanated from the Liffey in central Dublin, much of which ignored the obvious. A glance at a tidal atlas for Dublin Bay is enough to convince one that much of anything that gets dumped near the mouth of the Bay will get washed back in by the strong tidal currents. This can surely be described as the maritime equivalent of defecating on your own doorstep.

The Burford Bank straddles the mouth of Dublin Bay. It is an area of some very shallow depths. Part of the tidal streams run obliquely across the bank at various stages of the tide resulting in an increase in the rate of tidal flow. The depths here have found their own level over millenniums. Dredging spoil containing estuarine mud and fluvial silt is not going to remain in toto on the top of this bank. Ariel views have been taken in calm weather of the dark staining of much of the surrounding water that has been emanating from this dumpsite, and recently it has been possible to see this from the summit of Howth head.

A great many people are concerned about the possible detrimental effects of such pollution upon the flora and fauna of Dublin Bay. Sports scuba divers are among the most environmentally aware people in the country when it comes to matters concerning marine ecosystems. They are in a unique position to observe and monitor detrimental changes in the underwater environment. There are several such groups at present observing the situation in Dublin Bay, and they have expressed grave concerns about this matter.

Dublin Port management are to be greatly praised for the development of the Port into such a great commercial success. They are also to be admired for their policy of inclusivity with civic and sporting groups who use the Port and the Bay area. Few would deny the need for further expansion and improvement and this of necessity must include dredging operations.

However, all such development should not be to the detriment in any way of the precious and fragile facility with which we in Dublin are blessed.

Dublin Bay has been recognised by UNESCO as a unique environmental Biosphere. Long let it remain so. – Yours, etc,

CORMAC F LOWTH,

Member of the Maritime Institute of Ireland,

Dublin 24.