RIVER PROCESSES

Key Terms

The Hydrological Cycle

Evaporation is where water turns into water vapour and rises to form clouds.
Transpiration is water vapour released from plants, particularly from forests, which rises up into the atmosphere.
Precipitation is where condensed water vapour falls from the sky as rain, snow, hail, or sleet.
Interception is where precipitation hits trees or urban areas rather than getting directly to the ground.
Infiltration is where water seeps into the soil.
Percolation is where water seeps from the soil down into permeable rock below.
Throughflow is where water flows through the soil layer.
Groundwater Flow is where water flows through cracks in permeable rock.
Surface Run-off is where water flows overground (but not through streams/rivers).
Channel flow is where water flows in a stream or river.

River Systems

The drainage basin is the area from which the water flows into a single river.
The watershed is the edge of a drainage basin, boredering other drainage basins.
The source is the start point of a river where water flows out of the ground.
Tributaries are smaller streams that flow into the main river.
A confluence is where a trubutary meets the main river.

Hydrographs and Flooding

The discharge of a river is the amount of water flowing past a single point of a river at a singe point in time.
Hydrographs are graphs showing the discharge of a river over time after rainfall.
The lag time is the time between peak rainfall and peak discharge.
Flashy hydrographs are steep-sided with a high peak, and mean an area is far more likely to flood.
Subdued hydrographs are shallow with a low peak, and mean an area is much less likely to flood.

Erosion, Transportation and Deposition

Erosion is where material is removed from the sides/bottom of a river by the force of the water (either directly or by moving rocks).
Sand and stones scraping away at the riverbanks as they are moved by the river is called abrasion.
Rocks and stons wear and knock at each other. This process is called attrition.
Water can force itself into cracks into the bank. This process, hydraulic action, widens the cracks and breaks and erodes the bank over time.
Some minerals can be dissolved in the water - this creates a solution. Dissolved material is not carried by any of the below transportation process, as it is dissolved in the water.
Transportation is the transport of material down a river.
Small particles of soil and rock, in suspension, are carried along with the river.
Small stone bounce along the riverbed. This process is called saltation.
Larger stones roll along the riverbed, which is known as traction.
The bedload is the heavier material, carried along the bottom of the river.
Deposition is where material is dropped onto the bed of a river. Heavier material is deposited first, lighter material later.
Sediment is any material laid down through deposition.

Formation of River Landforms

Meanders are formed where a bend in the river increases over time. on the inside of the ben, the river is slower and so material is deposited, whereas on the outside and bottom the flow is faster and so material is eroded.

More Information on River Processes

Causes of Flashy Hydrographs

Case Studies

Boscastle, UK (Aug 2004)

Mozambique (Feb 2000)

Floods: Comparison Table

Factor Boscastle Mozambique
When 16 August 2004 February 2000
Deaths 0 Thousands
Rivers Valency, Jordan Zambezi, Save, Limpopo


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