Sir, - The idea of a Millennium commemoration barrage/ weir below the Matt Talbot Bridge, to provide a constant level Liffey Pond effect along the centre of the capital city, appears to have evoked a certain amount of interest.
However, a constant level Liffey Pond would be a such a change from the ages old normality of two tidal scours of the river bed each day, that one has to be very wary of the possible consequences. These would result from a drastic alteration of the natural river routine used by our city predecessors during centuries past, to save themselves from poisoning by self pollution.
in brief, it can be said that the river on every ebb tide scours out the huge volume of foul water (with its content nowadays, from an expanding population, of liquid rubbish production, and the silts associated therewith) which is fed continuously into the river by at least 16 tributaries from Islandbridge down to Matt Talbot Bridge. The continuous existence of a constantly high water level would cause these, mostly under ground, tributaries to back up and silt up, unless relieved daily by the ebbing tides.
Also, the main sewage system is such that in the event of a very heavy downpour of rain (especially if the tide is full in) the sewers have to be used as a dump of quite big capacity. This takes the surplus rainwater until the tide goes out, when the unusual and abnormal load of foul and rainwater can be dumped into the ebbing river through the very essential, if rarely used, ugly looking holes low down on the quay walls (at street ends approximately).
Such overloads occur rarely I understand, but must be dumped in Anna Livia as the last resort. Otherwise some of those lovely new underground car parks could be quickly back filled and nice new cars be found floating around in you know what! Perhaps consideration could be given to emptying the pool every night - with the necessary regard to the tidal positions and times - and thus scouring and evacuating the backed up tributaries contents, as well as removing any main sewer random flooding.
Again, in the event of an unusual and enormous downpour - such as the four inches of rain that fell in the city in one hour in 1962 - the authorities would have to empty the pool at top speed - bearing in mind the danger of water erosion of the barrage itself.
With these provisos - and there may be more - I Del that the idea of a beautiful pool in the city centre may be feasible, so as to welcome in the new Millennium. - Yours, etc.,
Rathdown Avenue,
Dublin 6.