AS levels - physical geography

Drainage Basin

Drainage Basin

Area of land drained by a river and its tributaries

Watershed

Dividing line separating two adjacent drainage basins

Mouth

End point of a river where it meets the sea

Tributary

A smaller river which joins a bigger river

Source

Where a river begins, usually in an upland area (may be from a spring or glacier or in a swampy area)

Confluence

Where a tributary meets the main river

Interception

When water does not reach the ground as it is trapped by trees

Stemflow

When water flows down the tree trunks or stems of plants

Surface storage

When water is held in lakes or puddles on the surface as it cannot be infiltrated into the soil

Infiltration

Process where water moves downwards through tiny pores in the soil

Soil moisture storage

Is when water is stored in the soil

Percolation

When water moves vertically down through the rock

Groundwater storage

When water is stored at depth in the rock

Transpiration

When water is removed from leaves into the atmosphere

Evaporation

Loss of moisture directly from rivers or lakes to the atmosphere

Surface run-off (overland flow)

When water does not infiltrate into the soil as it is too saturated and then moves if the surface

Throughflow

When water moves sideways through the soil

Groundwater flow

Slowest form of water transfer. When water moves sideways through the rock.

Phreatic zones

Permanently saturated zone within solid rocks and sediments

Water table

Upper limit of phreatic zone

Aeration zones/ vadose zones

Zone which is seasonally wetted and seasonally dries out

Aquifers

Layers of permeable rock containing significant quantities of water

Aquicludes/aquifuge

Large impermeable rocks which prevent large-scale storage and transmission of water

(A rock which won’t hold water)

Discharge

The volume/flow of water passing a river measuring station(gauging station) at a particular time

Flooding

An overflow of water from a water store onto land that is normally dry

Erosion

The breaking down of rock over time

Hydraulic action

The sheer force of water pounding into the bed and banks. Air is forced into cracks and compressed then expand explosively

Abrasion (corrasion)

Moving water throws particles it is carrying against the banks and bed which dislodges material.

Attrition

Particles being carries downstream knock against each other, wearing each other down, which results in smallerm rounder particles downstream.

Corrosion (solution)

Some rocks forming the banks and bed of a river are dissolved by acids in the water

Cavitation

Air bubbles trapped in the water are compressed into small spaces like cracks in the river’s banks. The bubbles eventually implode creating a small shockwave the weakens the rocks.

Traction

The heaviest particles are rolled along the bed. Such particles may only be moved when the river has a large volume of water in it.

Saltation

Heavier particles may not be held in the flow all the time but may be bounced along the bed.

Suspension

When particles are carried along in the flow and are not in contact with the river bed (often about 90% of load carried by stream)

Solution

Some minerals (particularly in limestone areas) dissolve easily in water and aren’t visible to the naked eye.

Competence (in terms of a river)

The largest particle a river can transport

Capacity (in terms of a river)

The total quantity of sediment a river can carry.