Rivers

Common River Terms • • • •

Source

– The place where a river begins.

Course

– The route the river takes to the sea

Tributary

– A small river that joins a larger river.

Confluence

– The point where the tributary joins the river.

Common River Terms • • • •

Mouth

the sea.

– The point where the river enters

Estuary

– The part of the mouth that is tidal.

Basin

– The area of land drained by a river.

Watershed

– The high ground separating one river basin from another.

The River’s Journey • • Rivers usually begin in the mountains. They flow downhill onto flat land and into the sea.

The Shannon’s Journey • The River Shannon is Ireland’s longest river.

• It flows from the Cuilcagh Mountains in Co. Leitrim to the Atlantic Ocean on the west coast of Ireland.

The Stages of a River’s Journey • As the river flows from it’s source to the sea it goes through 3 stages. These are, • • • The Upper or Youthful Stage The Middle or Mature Stage The Lower or Old Stage

The Youthful River • The youthful river has a small amount of water but it travels very quickly down the steep mountain slope.

• Most of its energy is used to erode (wear away) the landscape.

• This erosion (wearing away) occurs in 4 ways.

4 Processes of River Erosion •

Hydraulic Action

– The force of the moving water wears away the banks and bed of the river.

•

Abrasion

– Small stones carried by the river wear away at the the banks and bed of the river.

4 Processes of River Erosion •

Attrition

– The small stones in the river are worn down and broken up as they hit off each other.

•

Solution

– Rocks and soil are dissolved by acids in the water.

Landforms of the Youthful Stage • All of the erosion by the river creates features or landforms on the landscape. Three features created in the youthful stage are, 1.

2.

3.

V-shaped Valleys Interlocking Spurs Waterfalls

V-Shaped Valleys • V-shaped valleys get their name from their shape. The river erodes the landscape and creates a valley in the shape of a V.

• This occurs because of Vertical Erosion. The river cuts down into the river bed, making it deeper. It creates a narrow deep valley. Mechanical weathering and mass movement create the V shape. See Diagram.

V-Shaped Valleys

Interlocking Spurs • As the rivers flows it meets areas of hard rock. It cannot erode these so it flows around them.

• This creates a zigzag course. See Diagram.

Waterfalls • Waterfalls are formed when rivers flow over areas of hard and soft rock.

• The river erodes the soft rock but cannot erode the hard rock. This creates a step which the water starts to fall over.

• The falling water erodes deeper into the bed. The rivers load creates a Plunge Pool as it falls. See Diagram.

Waterfalls

The Mature Stage • We now know that during the youthful stage the river is mainly eroding the landscape.

• Erosion breaks off particles of rock and soil from the bed and banks of the river. They are carried along by the river and are known as the

Load.

• The load is carried from upland to lowland areas. This process is called

River Transportation.

River Transportation All rivers carry material in them. This material is carried by the river as it flows along.

Rivers can carry large stones, small stones, sand, and other dissolved minerals.

All of this material in the river is called the river’s

Load

When the river moves its load we call this

River Transportation

River Transportation • Transportation occurs in 4 ways.

• • • • 1. Rolling 2. Bouncing 3. Suspension 4. Solution

River Transportation Suspension Rolling Solution Bouncing

Rolling •

Rolling

– The large stones are rolled along the bed of the river.

Rolling

Bouncing

Bouncing

– The smaller pebbles are bounced along the bed of the river.

Bouncing

Suspension

Suspension

– Light material like sand and silt are carried along (floating) in the water.

Solution 4.

Solution

– Dissolved materials are carried along by the river.

Solution

Landforms of the Mature Stage In the Mature Stage the river begins to slow down, and so it begins to deposit some of its load. It creates the following features.

1.

2.

3.

Wide river valley Meanders Flood plain

Landforms of the Mature Stage Wider River Valley In the mature stage the river moves from side to side and the valley becomes wide and flat. Weathering and Mass Movement continue to wear away at the sides of the valley. See diagram.

Landforms of the Mature Stage Meanders Meanders are bends or curves along the river. They are formed by erosion and deposition. Erosion occurs on one side of the river while deposition occurs on the opposite side. This continues, making the bends sharper. See diagrams.

Meanders

Landforms of the Mature Stage

Flood Plain

A flood plain is the flat area of land on either side of the river. After heavy rain the river sometimes floods. The water spreads out over the land on either side of the river. When the river retreats it leaves behind a thin layer of

alluvium

. After many floods a thick layer of alluvium is created. This is very fertile soil.

The Old Stage • In the Old Stage the river is carrying lots of sand and silt. It is now flowing over flat land and so it is moving slowly. Therefore it begins to drop off its load. This is called deposition. Like erosion in the Youthful Stage, deposition also creates many features or landforms.

Landforms of the Old Stage The following features or landforms are created by river deposition in the Old Stage.

1.

2.

3.

Ox-Bow Lakes Levees Delta

Landforms of the Old Stage Ox-Bow Lakes An ox-bow lake is a horseshoe shaped lake found beside a river. Ox-bow lakes are formed when continued erosion and deposition create very pronounced meanders.

Eventually the river cuts through the neck of the meander.

Deposition then occurs which leaves the ox-bow lake separated from the river.

How an Ox-Bow Lake is Made

Landforms of the Old Stage Levees Levees are raised banks of deposited material found along the banks of the river. When the river floods and spreads out over the floodplain, the heaviest material is deposited close to the river.

Over time and after many periods of flooding this deposited material forms levees along the banks of the river.

Levees – Raised Banks

Landforms of the Old Stage Delta A Delta is a triangular shaped piece of land which is formed at the mouth of the river. As the river enters the sea it drops off all the remaining material it is carrying. This material builds up to form new land. The river is forced to break up into smaller channels called distributaries.

Rivers and People Rivers have always been important for people. In the past, people settled near a river as it provided them with food, water, defence, and an easy method of transport.

Nowadays, people try to control rivers to prevent flooding, for irrigation, to create electricity (HEP), and to create improved transport links.

Rivers are also important for tourism and leisure.

Hydro-Electric Power (HEP) Engineers build dams across the river. They can then control the flow of water in the river.

They release the water and use it’s power to turn large turbines.

Turning these turbines creates power which is used to generate electricity.