River Liffey
(Ireland)
The river
Liffey is one of the most important rivers in Ireland, it accounts for 60% of
Dublin’s fresh water. It flows through three counties, Wicklow, Kildare and
Dublin and stretches over 82 miles long. At its source, the Liffey is only 12
miles from the ocean, but as we know gravity guides water and adds an extra 70
miles to its journey from the mountains to the ocean. Upon first seeing the
Liffey the first thing you notice is the dark brown color of the river. This
signifies a rough ride from the source to the mouth of the river.
The Liffey starts at its headwaters
in the Wicklow mountains at an elevation of 1,600 feet between the Kippure and
Tonduff mountains. The terrain is rough and full of large granite rocks
deposited from glaciers. Not an easy hike, and comfortable shoes are needed.
The Wicklow mountains are known for their heavy rain fall and this causes a lot
of sediment production.
The sediment production is extremely corrosive,
as the rain fall in this mountain range is continuously year long and can
become extremely powerful in the wet winter months. This makes the Liffey a
perennial river as the large rainfalls keeps the river in constant motion. At its
source, the water has a turbulent flow which can quickly change and sculpture
the path of the river and the terrain.
The terrain that surrounds these mountains is mainly consisting of granite
with a top level of mud and clay. The bed of the river in this region is
bedrock with very little dirt, which makes the river’s water clear. The banks
of the river are surrounded by rough pointy granite, in which the river has eroded
the top level of soil exposing the granite. This makes the terrain extremely
vulnerable against large volumes of rain fall and has resulted in the formation
of a V-shaped valley that flows between the Kippure and Tonduff mountains. This
V-shaped valley is where its major tributaries include the River
Dodder, the River Poddle and the River Camac flow into one to make the
Liffey. Flooding in this area is highly unlikely as the gradient slopes down to
the lowlands.
As the river makes its way down
from the mountains, we find its path has brought it to County Kildare. When it
reaches this area, the river reaches its Sediment transport area. Here the
rivers discharge slows down, and the erosion is not as damaging as the sediment
production stage. This is where the Liffey water starts to darken as the runoff
from the Sediment production slows down to produce a dark murky water.
Dendritic pattern is the most
prevalent drainage pattern on the Liffey’s path. This is due to the slope of
the land. The Liffey starts at the top of a mountain and works its way down to
the ocean. But a funny fact about the Liffey is that at its source it is only
12 miles from the ocean, but because water is influenced by gravity, it slopes
away from the ocean and heads back into mainland Ireland. This region is mainly limestone and this
sediment rock is weak against the corrosive powers of the river. The gradient
in this area is almost flat, but the powerful force of the rivers flow velocity
from its source helps the river carve its way through this region. This causes
the river to meander through the flat lands of Kildare (Known for its flat and
fertile agricultural land). Due to its geographical location, Kildare is
considered a flood plain and usually floods after a heavy week of rain. Although
both sides of the river have natural levees, they are unable to hold the
overflow in heavy rain conditions. Both sides of the riverbed are surrounded by
back swamp, which indicates that floods are very present in this area. Luckily most of the land that surrounds the
river is agricultural land and does not cause a mass concern for large
populated towns in the region.
This has caused the formation of
many Oxbow lakes along the rivers path, shortening the gap to the ocean. Most
of these Oxbow lakes have dried up but in some ephemeral cases at high water
levels some of these Oxbow lakes can become part of the river again until the
water levels retreat.
As the river reaches the graded
conditions downcutting becomes less dominant. The meandering pattern causes the
energy of the river to erode the sides or banks of the river, resulting in the
valley widening. At its heaviest turbulent flow, the Liffey is measured at 25
feet wide, but once it reaches its graded conditions the river can widen up to
70 feet wide.
Sediment Deposition is where a
river meets the ocean, for the Liffey this happens in the heart of Dublin City.
In the Gaelic language Dublin is known as Baile Atha Cliath, translated into
English it means the Black River. This is due to the large discharge of water
slowing down and turning into a laminar flow as it approaches the ocean. This
murky water is a result of sediment deposition as the river loses power the
sediment is deposited at the mouth of the river, resulting in a dark sediment
depository consisting of mud clay and sand particles. Most of these sediments are washed out to
sea, but the Irish government does have to dredge the riverbed every couple of
years. This is due to the fact that Dublin Port sits on the river’s mouth, and
for hundreds of years this was a major port for trading importing and exporting
goods. So, to keep this trade route open for business the delta which once sat
at the rivers mouth has long being dredged so larger boats can enter the port.
As the river enters Dublin city, it
is surrounded by large walls that act as levees. These levees have a 20-foot
clearing from its water level. This is to prevent floods within the city, as
history shows floods were not unusual until the building of these manmade
levees. In the last century, Dublin city only flooded once since the levees
were put in. So, this is a good indication that the city of Dublin is well
protected from flooding.
One interesting fact about the
Liffey is that it runs most of its course over limestone. This sedimentary rock
formed millions of years ago beneath the sea. This has an important impact on
the river as limestone is more alkaline, creating more conducive conditions for
fish such as trout to thrive. This one of the main reasons Dublin became a
settlement for its fresh water and unlimited fish.
The
Nazca Plate is an oceanic tectonic plate in the eastern Pacific Ocean basin off
the west coast of South America. The ongoing subduction, along the Peru-Chile
Trench is greatly responsible for the Andean orogeny. The Nazca Plate is
bounded on the west by the Pacific Plate and to the south by the Antartic Plate
through the East Pacific Rise and the Chile Rise. Its movement has created some
volcanic islands, as well as east-west running seamount chains that
subduct under South America. It is a relatively young plate both in terms of
the age of its rocks and its existence as an independent plate having been
formed from the break-up of the Farallon Plate about 23 million years ago.
