HideShow resource information
  • Created by: Hannah
  • Created on: 02-04-13 15:07


Corrasion- River picks up materail and rubs it against bed and banks. Most effective during times of flood.

Attrition- Boulders collide and break into smaller peices. Over time, rocks become more rounded.

Hydraulic Action- The force of water that hits river banks and pushes its way into cracks. Air becomes comprssed, preasure increases and river bank may collapse.

Solution- The result of chemical composition on the water.

1 of 15


Suspention- Very small particles of clay as silt are carried in the water. the higher the velocity, the more paticles it can pick up.

Solution- The acids in the water can dissolve bedrock.

Slaltation- Pepples, sand and gravel are lifted up by the current and bounce along the bed.

Traction- Larger boulders roll along the river bed as they are too heavy to be liften. Happens in times of great flood.


Sediment may be deposited because of low rainfall, shallow water, river entering sea/lake, increased load and rivers overflowing its banks, therefore depositing material on the flood plain.

2 of 15


V-Shaped Valleys and Interlocking Spurs

  • In the upper part of a river, vertical erosion is common creating a steep sided river valley.
  • Interlocking spurs form as the river has to take a winding course due to the highland areas that jut out.


  • Waterfalls form as a result of a river that has flowed over hard rock and meets a band of soft rock.
  • The velocity increases as the water nears the edge of the fall because of a decrease in friction as the water is no longer in contact with the river bed
  • the soft rock is worn away and over time, the hard rock is undercut and may collapse.
  • Plunge pools are common at the base of waterfalls.
3 of 15



  • If the gradient of a river increases quickly or flows over gently dipping areas of harder rock rapids will result.

Flood Plains

  • This land more likely to experience flooding.
  • If a river floods, silt is deposited on the land increasing its fertility and the height of the flood plain increases.
  • The flood plain can be made wider by the lateral erosion of meanders.
  • The edge of a flood plain is marked by a clear slope called a bluff line.


  • At some times of the year, due to snowmelt, rivers  may carry a very highload in comparison to their velocity and the channel can therefore become full of sediment.
4 of 15



  • If a river floods, material is deposited on the banks. The material that is dropped first is the coarsest and creates a natural embankment.
  • When the amount of water in the river is low deposition takes place, the bed of the river rises and flooding is likely.
  • in some countries, artificial levees are put in place to reduce the flood risk


  • These are made of fine sediment and occur when a river has a decrease in energy as it enters the lake or the sea.

Pools and Riffles

  • These occur due to both erosion and deposition. Pools are areas of deeper water and riffles are areas of shallow water. A pool has more erosion than a riffle and is caused by turbulance.
5 of 15



  • Meanders form where alternating pools and riffles develop at equally spaced intervals.
  • The river has more erosive power and greater energy in the deep pools.
  • Energy is lost as the river flows over a riffle because of friction.
  • Turbulence increases in and around pools as the water speeds up, causing the flow of water to begin to twist and coil.
  • This causes corkscrew-like currents in the river called helicoidal flow, which spiral from bank to bank between pools.
  • The helicoidal flow causes more erosion and deepening of the pools. It also causes eroded material to be deposited on the inside of the next bend, where the river loses energy.
  • The combination of erosion and deposition exaggerates the bends until large meanders are formed.
6 of 15


Oxbow Lakes

  • Oxbow lakes are formed when the neck of the loop of a meander is broken through, often during flooding.
  • Deposition dams off the loop, leaving an oxbow lake.
7 of 15

The Graded River and Base Level

Changes in Base Level

Base Level: The lowest point to which erosion by running water can occur. For rivers, the base level (limit) is usually the sea.

Causes of a Change in Base Level

Climatic Change- Glaciations and changes in rainfall.

Tectonic- Where land is uplifted after plate movement or volcanic activity. Changes can be positive (sea level rises in relation to the land) or negative (sea level fall in relation to the land).


If land emerges from the sea following a negative change in base level, the potential energy of a river for erosion is rivived and a re-grading of the river can occur.

8 of 15

The Graded River and Base Level

River Terraces

River terraces are the remains of former flood plains that lie far above the extent of present day flooding as a result of vertical erosion caused by rejuvenation.

Incised Meanders

If land is uplifted for a considerable period of time, a river may cut downwards anf form incised meanders. The 2 types of incised meanders are:

Entrenched meanders- Symmetrical cross section, and occur if valley sides are resistant to erosion, or rapid incision by the river.

Ingrown meanders- Less rapid uplift of land, allowing river to shift laterally across floodplain.

9 of 15

River Flooding

Causes of Flooding:

  • Basin size
  • Precipitation
  • Temperature
  • Land use
  • Geology
  • Soil type
  • Drainage density
  • Tides
  • Urbanisation
10 of 15

River Flooding- Case Study

River Ouse Flood, Yorkshire, 1982


  • Initial snowfall from deep depressions
  • Subsequent warmer temperatures, heavy rainfall and rapid snow melt
  • Smaller rivers unable to cope with amount of water
  • Infiltration capacities exceeded resulted in much overland flow
  • Increased overland flow in urbanised areas


  • Destuction of communications and buildings
  • Loss of life and property and destruction of crops
  • Drainage problems
  • Spread of disease and impacts on the economy
11 of 15

River Flooding- Case Study


  • 800 properties were flooded
  • 19,000 hectares of agricultural land under water
  • Military assistance was needed to distribute food and protect property in York, Selby and Boroughbridge
  • Commercial properties were flooded with water to a depth of about 1 metre.


Regulate Land Use

Aim: Promote wise use of land, to reduce flooding and limit building

Advantages: Cheap, immediate effect, long term, provide for most suitable use of land

Disadvantages: Doesn't prevent floods, not always applied well or to existing land uses

12 of 15

River Flooding- Case Study

Dams and Reservoirs

Aim: Protect existing land uses, limit flooding, promote recreation

Advantages: Protects existing land uses, controls water flow, allows recreation

Disadvantages: Costly, lengthy construction, maintenance needed, wildlife destoyed, communities disrupted, sedimentation

Land Treatment

Aim: Promote soil and water conservation, reduce flood levels

Advantages: Cheap, attacks flood problem at source

Disadvantages: Not always relevant, limited effect

13 of 15

River Flooding- Case Study

Acquire Flood Plain Land for Public Use

Aim: Reduce losses from floods

Advantages: Permanent, numerous benefits

Disadvantages: Costly, sites not always suitable for other uses, land shortage may result

Insure Against Floods

Aim: Promote flood regulations

Advantages: Spreads cost of flood losses

Disadvantages: Can be costly


14 of 15

River Flooding- Case Study

Install Warning Systems

Aim: Warn property owners of threats, allow for evacuation

Advantages: Allows people to adjust to the flood threat

Disadvantes: Requires education, systems must be carefully maintained

15 of 15


No comments have yet been made

Similar Geography resources:

See all Geography resources »See all Rivers and fluvial processes resources »