NB: When answering questions on River features, always remember to use the F.E.E.D. system. (Feature, Explanation, Example, Diagram)
Definitions of main features
Source– Where a river begins.
Tributary– Smaller rivers/streams that join the main river.
Confluence– The point where two rivers join.
Estuary– The part of the river (mouth) which is tidal.
Mouth– Where the river enters the sea/lake.
Watershed– The area of high land that separates two basins.
Course– The route taken by a river between its source
and its mouth.
River Basin– The total area drained by a river and its
Activities of a River
Four types of Erosion
Hydraulic Action- The force of the water.
Abrasion– The load hitting the bed and the banks.
Attrition– Load hitting against load and eroding.
Solution– Some rocks such as Limestone can dissolve due to acids in the water.
Rolling- Larger rocks and boulders.
Bouncing- Smaller rocks.
Suspension- Light particles are carried in the water.
Solution- Some rocks are dissolved in water.
(Loss of energy = has not got the energy to carry the load so it has to drop it)
– Loses speed and hasn’t the energy to carry the load.
– When the river meets resistance when trying to enter the sea or lake.
3 Stages of a River
YOUTHFUL STAGE (UPPER COURSE)
– V- Shaped Valley > Erosion
– Interlocking Spurs > Erosion
– Waterfalls > Erosion
– Potholes > Erosion
MATURE STAGE (MIDDLE COURSE)
– Meanders > Erosion and Deposition
OLD AGE STAGE (LOWER COURSE)
– Floodplains > Deposition
– Ox-Bow Lakes > Erosion and Deposition
– Deltas > Deposition
– Levees > Deposition
The Young Stage
The river is usually small and flows down steep slopes with lots of energy. The features found in the youthful stage of a river are all formed by the processes of Erosion.
The river will erode downwards in its youthful stage. This is called vertical erosion. This leaves steep sides which are exposed to weathering which in turn loosens and eventually breaks up the rock and soil. This loose material will then fall into the river and be transported downstream. The result is a valley with steep sides and very narrow floors which looks like a “V”.
EXAMPLE: Upper course of the River Finn at Glenfin, Co. Donegal.
In its youthful stage the river has very little power to erode. As a result, when it meets with obstacles of hard rock it is unable to cut through them and so has to flow around them. This leaves interlocking spurs of high ground jutting out on both sides of the valley.
EXAMPLE: Upper course of River Finn at Glenfin, Co. Donegal.
Waterfalls are found where there are different types of bedrock i.e. where soft and hard rock lie side by side. While the river is able to erode the soft rock, it is unable to erode the hard rock. As a result of this a difference in height begins to form and a waterfall is created as the water drops from one level to the other. The force of the water and the debris carried by the river down the slope creates what is known as a plunge pool at the base of the waterfall.
EXAMPLE: Glencar Waterfall, Co. Leitrim.
(Glencar Waterfall, Co. Leitrim)
Potholes are formed from hollows in a rivers bed. Water and its load (pebbles) flow into the hollow and the force of the current and the swirling action of the pebbles causes the hollow to become wider and deeper to form a pothole.
Eg. Upper course of River Finn, near Glenfin.
The Mature Stage
In the mature stage of a river the slope becomes gentler and the river becomes much wider as it is joined by many tributaries. The river is also carrying a load now that has been eroded from further upstream.
Meanders are bends or curves which are found in the mature stage (middle course) of a river. As the land is much flatter than it was in the youthful stage the river tends to swing from side to side. As it does so the current will be stronger on the outside of the bend and so Erosion will take place, while on the inside of the bend the current flows more slowly so Deposition will take place.
EXAMPLE: Middle course of River Finn at Ballybofey, Co.Donegal.
A Meander on the River Finn
The Old Stage
At the Old age stage the river is usually at it’s widest. The land is also at its flattest. This means that the river has to work very hard to make its way to the sea. The main agent at work now is Deposition.
Ox-Bow lakes are Horse-Shoe shaped lakes which are found near the end of a rivers course (Old Age Stage). During times of flooding there will be an increase in the speed and volume of a river. Therefore when a river comes to a tight meander that it cannot go around it simply bursts its banks and cuts through the bend. The water which flows around the bend will now be flowing slowly and so deposition will take place. Over time the meander will become cut off from the main river because of deposition. The cut off meander is then called an Ox-Bow lake.
EXAMPLE: River Moy, near Foxford, Co.Mayo.
Floodplains are almost flat plains of land which lie at the sides of rivers that are in their old stage. During times of heavy rain the river may rise until it breaks its banks and floods the surrounding flat land. When the floods eventually subside, thin layers of Alluvium are deposited on the land. When the river has flooded many times the layers build up into a thick fertile covering over the floodplain.
The River Finn flooding at Dreenan, Ballybofey
Levees are long narrow ridges of Alluvium which are found along the banks of many old rivers. They are formed as a result of flooding. Each time the river floods it will carry its load out to the floodplain as it has a great deal of energy. However, when the flood subsides it does not have the energy to carry the load back into the channel and so deposits it. After numerous floodings these deposits build up to form Levees.
EXAMPLE: The old age stage of the River Finn outside Ballybofey.
A Delta is a triangular area of land which has been formed by a river depositing its load as it enters the sea or a lake. A delta will only form if a river has been carrying a large load of Alluvium and the alluvium is being dropped off at a faster rate than the tides/currents can carry it away.
The streams that a river divides up into to make its way around the deposited material are called Distributaries.
EXAMPLE: The Mouth of the River Nile, Egypt.
Uses and Advantages of Rivers
- Dams may be built on rivers to produce Hydro-Electric Power HEP ( A cheap, renewable source of electricity
- Leisure/Sport/Recreation……… Fishing, Canoeing, cruising. Fishing attracts tourists, freshwater cruising on the Shannon.
- Irrigation (Artificial watering of crops) eg: Plain of Lombardy, Italy. Very important for agriculture. River Po and its tributaries used to water crops.
- Scenic Attraction.
- Boundaries between Countries and Counties.
- Provides Fertile land
- Flooding – Damage to property, land, animals and homes. Valuable crops destroyed, Loss of Life, Famine or food shortage.
- Carry pollutants. From factories and farmland which can harm livestock fish and other animals.
- Carry diseases. Helps to spread deadly diseases in Third World countries.
Dam building in Ireland
Hydro-Electric power stations which use rushing water to generate electricity have been built on the rivers throughout Ireland. As part of the schemes a dam is built across the river valley. Behind the dam, trapped water rises to form an artificial lake.
- They enable Hydro-Electric Power to be generated.
- Artificial Lakes can be used as reservoirs for Urban water supplies.
- Artificial Lakes can be used for Fishing and other water sports.
- Artificial Lakes flood settlements and valuable farmland.
- The survival of Salmon and other river creatures may be threatened.
- It is difficult and expensive to dam a river.
Cathleen’s Falls H.E.P. station in Ballyshannon.