This PowerPoint lecture will provide you with a quick introduction to Cork Harbour

Transcription

1 This PowerPoint lecture will provide you with a quick introduction to Cork Harbour

2 Cork Harbour is arguably one of the biggest natural harbours in the world. It provides access to the sea for the historic port city of Cork and contains a busy container port (see picture). The town of Cobh was the departure point for penal exiles and emigrants in former years, famously the last port of call for the ill fated Titanic. The harbour, with its dredged channel, still provides access to cruise liners (see picture), oil tankers and container ships. Haulbowline Island is the base for the Irish Naval Service and home port to the naval fleet. The Harbour used to support a fisheries both for fish and oysters. It is the focus of major local industry including pharmaceutical plants, and oil terminal and refinery, power station and formerly steel plant and fertiliser plant 2

3 Cork Harbour is a flooded river valley (or ria) as a result of post-glacial sea level rise. The surrounding topography is geologically controlled (see next slide) with a anticline core sandstones forming uplands and softer limestone dominating the syncline cores forming east-west trending valleys. In the harbour channels cut inland northwards crosscutting the geology with expansive harbour areas adjacent to the lowlying areas and narrower channels cutting through the uplands. These narrow channels and the harbour mouth follow north-south faults and maybe relics of a former Cenozoic north-south drainage system (the modern Munster drainage network largely running east-west entrained within the synclinal valleys). The Harbour is fed principally by the River Lee (flowing through Cork City) and the much smaller R. Owenacurra that flows through Midleton and the R. Owenabue that flows through Crosshaven. The freshwater influence from the Owenabue can be picked up in the Harbour Mouth. Several islands exist in the Harbour, the largest being Great Island which hosts Cobh. Despite the areal extent of water in the harbour, most of the harbour is shallows of only a few metres deep. A deep navigable channel runs from the Harbour Mouth north to east of Cobh where it turns abruptly infront to Great Island heading west to Monkstown before turning again north through Passage West and on up to the City. The Owenabue is also navigable to moderate sized craft. The River Lee is tidal to the western edge of the city. 3

4 The Geological Map (GSI) shows the east-west striking bedrock geology displaced by north-south faults. The north-south channels making up the harbour excavate the weaknesses of the faults. Large flooding areas are underlain by the purple and blue coded lithologies which are softer limestones. The lithologies are folded into anticlines and syncline (during the Hercynian orogeny), the erosion of which reveals a north-south repetition of geology. Blue and purple coded limestones for the cores of synclines and green and brown coded sandstones form the cores of anticlines. The lithologies are (from north to south): BS (brown) Upper Devonian): Ballytrasna Fm Purple mudstones with some sandstone GY (green) Upper Devonian: Gyleen Fm Sandstone with mudstone & siltstone KN (green/blue) Carboniferous : Kinsale Fm Grey mudstone with subordinate sandstone BA (blue) Carboniferous: Ballysteen Fm Fossiliferous dark-grey muddy limestone WA (purple) Carboniferous: Waulsortian Limestones - Massive unbedded fine-grained limestones CK (red) Carboniferous: Cork Red Marble Fm Red brecciated calilutite limestone LI (blue) Carboniferous: Little Island Fm Massive and crinoidal limestone CV (blue) Carboniferous: Clashavodig Fm Oolitic, peloidal, cherty fine limestone 4

5 Despite the areal extent of the harbour. Most of it is shallow being nearly exposures a lowest tides. Navigation at low tide, and for all sizable vessels, is confided to the channels which wind through the estuary. The main channel is dredged to allow access to large cargo ships reaching depth of 10-15m. The harbour mouth contains a submerged rock near the middle of the channel which is a navigation hazard to large vessels only.

6 Transitional waters mapped in Cork Harbour as defined by the EPA 6

7 Cork Harbour is a mosaic of sediment types. Small changes in sediment type can result in very different benthic communities being present. Each of the stations marked are to some degree gravelly muddy sand and the resultant fauna as you can see from the pictures is very different with brittle stars dominating the first station, large errant polychaetes (Nephtys species) the second and a more diverse fauna with a variety of polychaete species occupying the third sample. 7

8 Multibeam bathymetry outside the harbour mouth (Infomar) shows that most of the area is dominated by exposed rock on the seabed. Nearer the harbour mouth a large expand of sand, gravel and shell hash is found. As one moves offshore this is confined to gullies in the rock. The old submerged palaeo-channel of the River Lee can be seen heading straight out

9 A close up of the River Lee palaeo-channel. The east-west strike of the bedding is clearly visible in the rock and different lithologies revealing different seabed morphologies. Unconsolidated sediment in the palaeo-channel is heaped into drifts The straight line running down the channel is a gas pipeline going to the Kinsale Gas Field

10 Cork Harbour is strongly tidal all the way to the western edge of Cork City. The main harbour is brackish and a mixing zone for sea water and river water. Stratification occurs in the harbour with the more buoyant freshwater river water flowing over the more saline seawater coming in the with tide through the harbour mouth. The bottom image shows salinity. The incoming seawater (red) flows under the river water but also backs it up as the tide pushes up estuary. In winter with strong river flood, the river water can flow all the way over the saltwater wedge and out to sea. It is possible to get surface water flowing seaward at the same time as more brackish benthic water flow up-channel. The top image is temperature and was taken in November. Here the river water is colder than the sea. The opposite is the case in summer.

11 Cork Harbour is a major industrial port as well as a focus for recreational activity and urbanisation. Urban developments all feeding into the harbour include Cork City, Midleton, Cobh and Carrigaline as well as lesser developments. These all have an impact on water quality although less so than in the past. Industrial developments and associated discharges include Whitegate oil refinery, ESB power station and a number of pharmaceutical plants. Former major industries include a fertiliser plant and metal works which is a controversial source of alleged toxic pollution. The Harbour has deep berths for ferries and cruise ships as well as a busy container port. Sailing is popular in the harbour. Being a busy confined estuary, water quality is under pressure. A major sewage treatment plant for Cork City and area has significant improved water quality. The area supports important habitats especially for wading birds. The harbour used to support an oyster, shellfish and fin fishery which has largely collapsed

12 Protected Areas (SAC, SPA, pnha) within Cork Harbour Cork Harbour hosts a number of Natura 2000 sites including the Great Island Channel SAC andcork Harbour SPA 12