Rivers

Water cycle definition

The continous circulation of water between land, sea and air

Drainage basin definition

an area of land drained by a river and all of its tributaries

precipitation definition

a form of moisture in the atmosphere such as rainfall, sleet, snow and fog falling into the drainage basin

interception definition

the process whereby precipitiation is prevented from falling onto the ground by plants. It slows run0off and reduces the risk of flash flooding.

throughflow definition

water which is moving throug the soil

percolation definition

the movement of water from the soil into the bedwork

surface runoff / overland flow

water which is moving over the surface of the land

groundwater flow

water which is moving horizontally through the bedrock toward s a river or sea

evapotranspiration

the process by which water is transferred from the land to the atmosphere by evaporation from the surfaces e.g lakes , and by transpiration from plants

watershed

the boundary between drainage basins, it is often a ridge of high land

source

the starting point of a river it may be a lake , glacier or marsh

tributary

a stream which flows into a large river

confluence point

the point where two rivers meet

river mouth

the end of a river where it meets the sea, ocean or lake

gradient

the slope over which the river loses height

Why does gradient decrease with distance from source

In the upper course the river is eroding its channel vertically which produces a steep gradient. In the lower course the river is eroding laterally (sidewards) which creates a gentler gradient.

velocity with distance form the source

Increases

Reason why velocity increases with distance from the source

At the source the river is flowing slowly even though the land is steep. This is because the discharge is low and large angular boulders in the river bed create a lot of friction. At the mouth, the river flows much faster than at the source even though the land is more gently sloping. This is because each of the tributaries have now added their water (high discharge) and the bed load is small and rounded so little energy is lost by friction.

Velocity may be unusually high where:

• A tributary joins and discharge increases suddenly

• Slabs of smooth rock on section of river bed create little friction

• Large angular stones have been removed from river bed (reduce flooding build walls)

  • Steep gradient

Velocity may be unusually low where

• discharge is reduced- permeable rocks absorb water

• Obstructions in river - trees, bridges

• Bedload is large and angular

• Gentle gradient

Discharge with distance from the source

Increases

Why does discharge increase from source

As tributaries join the main channel, their water flows into the river. At the mouth all the tributaries have added their water so discharge is at its highest. With more water in the channel, there is less friction so the water flows faster.

discharge may be unusually high due to

• Land drainage by farmers brings water from the land to the river

• Impermeable rock surfaces - water moves quickly to the river by surface runoff

• Tributary joining main river - a large tributary brings a lot of water to the river

Discharge may be unusually low due to

• Mature Forest - trees intercept water, infiltration, loss of water as trees suck up the water - a small amount of water moves slowly to river by throughflow

• Permeable rocks - soak up and store water

Width with distance from source

Increases

Reason why width increases from source

At the source the river has very little energy as discharge is low and there is a lot of friction with the large, angular bedload. With distance downstream, there is more water in the channel and little energy is lost due to friction as the bedload is small and rounded. The river has lots of energy so erodes its banks (lateral erosion) by hydraulic action and abrasion to create a wide channel

Depth with distance from the source

Increaes

depth

the distance from the surface

width

the measurement from one river bank tot he other across a river channel

load

the sediment carried by a river

river discharge

the amount of water in a river which is passing a certain point in a certain time. it is measured in cubic metres per second,

how to calculate river discharge

multply cross sectional area ( depth x width) by velocity

erosion

wearing away of the landscape by the action of ice, water and wind

deposition

when a river drops the load that its carrying. This can be because the river has slowed down and has less energy. The largest material is dropped first.