Flood!

A Long History of Flooding in Cork

Since the last glaciation ended, 11,600 years ago, the continuous flooding, which has been typical of the River Lee, is one of the key factors that has caused thick fluvial deposits to accumulate in the Lee valley. Engineering boreholes demonstrate that a thickness of at least 40m is present in the deepest part of the valley at Cork.  Another key factor is the progressive rise in sea level that has occurred during the postglacial period because this change forced a similar increase in water table level.

South Channel of the River Lee, The Gearagh, near Macroom, Co. Cork. Photograph: Anthony Beese.
South Channel of the River Lee, The Gearagh, Macroom, Co. Cork. Photograph: Anthony Beese.

Initially, periodic flooding with huge volumes of melt water generated the mixed deposits of sand, gravel, cobbles and boulders that have been encountered at depth. As the valley became infilled, and as water levels rose, the coarse outwash from the melting glacier was replaced by sand- and gravel-rich sediment deposited initially, in fast-flowing braided streams, and then, by a branching river that flowed down a shallow gradient; also known as an anastomosing river.  Thus, in the Late Mesolithic, the valley at Cork may have been similar to the unique, forested floodplain that is preserved at The Gearagh, near Macroom, further upstream. Unfortunately, much the unique environment was drowned in the 1950s, when two dams were built  on the River Lee as part of the ESB hydroelectric scheme, so that now only oak stumps and half-submerged channels remain (see featured image).  Some idea of the impassable woodland in the upper part of The Gearagh does, however, survive and is shown in the image on the left.

The fish trap discovered by archaeologists on Victoria Quay. Image: Diageo and TheJournal.ie
The fish trap discovered by archaeologists at Victoria Quay, Dublin.  Image: Diageo Ireland.  See TheJournal.ie

Thus, it seems likely, that about 6,200 years ago (Beese 2013), fishermen in small boats navigated through a network of channels and set fish traps like those recently discovered in Dublin (see image), which are also thought to date to the late Mesolithic (McQuade 2007, Halpin 2013). Eventually, the sea, which had already transgressed into Cork Harbour, spread the estuary as far as the locus of Cork.

However, even though rising sea levels had begun to stabilize, the periodic flooding continued. The different factors, which are complexly interrelated, include not only climate change, as yet not properly determined, but also the peculiar fluvial and marine topography at Cork and the large catchment of the River Lee (1,151 km2).  In addition, the major changes in land use both upstream and at Cork itself must also play a significant part.  Indeed, many of the factors that generated high water levels along the Thames valley last winter are probably also applicable to Cork (see appraisal by Robert Van de Noort 2014).

In summary, the long history of flooding made life difficult for the city’s first inhabitants and continues to cause problems for those that live there now. For Cork lies in a narrow valley and is in the way of both river and sea; being caught between the opposing flows of the River Lee.