GEOMORPHOLOGY
,CHAPTER 1: DRAINAGE SYSTEMS IN SOUTH AFRICA
KEY TERMS:
Catchment area: an area where the river gets its source of water – total area that provides water to the
drainage basin. The water comes from rainwater, which flows down the slope, and from underground
water, which seeps into the river.
Drainage basin: area drained by a river system
Drainage density: the total length of streams per unit area of a drainage basin – high surface runoff = high
drainage density
River system: the main river and its tributaries and channels
Drainage pattern: surface pattern formed by a river and its tributaries
Base level: the lowest level to which can erode
Source: place where a river begins (headwaters)
Mouth: where the river ends - flows into the sea or a lake
Surface runoff (overland flow): rainwater flowing over the ground surface. (happens during heavy rain or
when soil is already saturated)
Watershed: high ground separating two drainage basins (high-lying land separating two river valleys)
Stream or river network: individual streams and rivers that are connected
Tributaries: individual river channels that feed into the main channel and form the stream network
Distributaries: small streams that break away from the main river when it enters an ocean or sea
Confluence: point where two rivers meet
Interfluves: ridges of high ground between individual channels (a.k.a spurs)
Overland flow: rainwater flowing over the surface
Channel flow: water flowing in a river channel
Through flow: water flowing through the soil
,Groundwater: water that is found underground in the pores and cracks of rocks
Groundwater flow: water flowing through underground rocks
Permeable rocks: soft or porous rocks that allow water to seep through
Impermeable rocks: hard rock that does not let water penetrate or pass through
Water table: upper level of the underground water. Below the water table the rock is satuarted
Base flow: groundwater that seeps into a river
Exotic river: area supplied with water where the river rises but very little water is added as they flow
towards the sea – the river originates in a high rainfall area and passes through arid or dessert area
Permanent/perennial river: flows all year round
Seasonal/non-perennial river: flows only during rainy season
Superimposed stream: a river that is younger than the underlying rock structure on which it flows
Antecedent stream: a river that is older than the underlying rock structure on which it flows
Rejuvenation: a river that gains energy and erodes vertically or deeper
Head waters: a tributary stream of a river close to or forming part of its source
River capture/stream piracy: a process where one river robs another river of its headwaters
Radial patterns: develops in a dome where streams flow outwards and downhill
Trellis pattern: forms on inclined strata that are unequally resistant to erosion, or in areas where there are
parallel fold mountains
Strata: rock layers
Rectangular pattern: forms on igneous rock that has joints and cracks; the streams develop right-angled
bends where joints meet
Centripetal pattern: streams flow into a central pan or low-lying area
Dendritic pattern: has a tree-like appearance; forms on rocks of similar hardness in an area with a similar
gradient
, Parallel pattern: develops on a surface that slopes uniformly but is fairly steep; the river and its tributaries
flow downslope nearly parallel to one another
Deranged pattern: no apparent drainage pattern
Stream order: the category of a stream in a network determined by the order of the streams feeding into it
Discharge: the amount of water flowing in a river channel past a point in a given time – volume of water
flowing through a river channel per unit of time.
Laminar flow: water flowing in sheets/layers; it does not change levels
Turbulent flow: water flowing in a bubbling motion; it changes levels – characterized by chaotic changes in
pressure and flow velocity
,CHAPTER 1: DRAINAGE SYSTEMS IN SOUTH AFRICA
KEY TERMS:
Catchment area: an area where the river gets its source of water – total area that provides water to the
drainage basin. The water comes from rainwater, which flows down the slope, and from underground
water, which seeps into the river.
Drainage basin: area drained by a river system
Drainage density: the total length of streams per unit area of a drainage basin – high surface runoff = high
drainage density
River system: the main river and its tributaries and channels
Drainage pattern: surface pattern formed by a river and its tributaries
Base level: the lowest level to which can erode
Source: place where a river begins (headwaters)
Mouth: where the river ends - flows into the sea or a lake
Surface runoff (overland flow): rainwater flowing over the ground surface. (happens during heavy rain or
when soil is already saturated)
Watershed: high ground separating two drainage basins (high-lying land separating two river valleys)
Stream or river network: individual streams and rivers that are connected
Tributaries: individual river channels that feed into the main channel and form the stream network
Distributaries: small streams that break away from the main river when it enters an ocean or sea
Confluence: point where two rivers meet
Interfluves: ridges of high ground between individual channels (a.k.a spurs)
Overland flow: rainwater flowing over the surface
Channel flow: water flowing in a river channel
Through flow: water flowing through the soil
,Groundwater: water that is found underground in the pores and cracks of rocks
Groundwater flow: water flowing through underground rocks
Permeable rocks: soft or porous rocks that allow water to seep through
Impermeable rocks: hard rock that does not let water penetrate or pass through
Water table: upper level of the underground water. Below the water table the rock is satuarted
Base flow: groundwater that seeps into a river
Exotic river: area supplied with water where the river rises but very little water is added as they flow
towards the sea – the river originates in a high rainfall area and passes through arid or dessert area
Permanent/perennial river: flows all year round
Seasonal/non-perennial river: flows only during rainy season
Superimposed stream: a river that is younger than the underlying rock structure on which it flows
Antecedent stream: a river that is older than the underlying rock structure on which it flows
Rejuvenation: a river that gains energy and erodes vertically or deeper
Head waters: a tributary stream of a river close to or forming part of its source
River capture/stream piracy: a process where one river robs another river of its headwaters
Radial patterns: develops in a dome where streams flow outwards and downhill
Trellis pattern: forms on inclined strata that are unequally resistant to erosion, or in areas where there are
parallel fold mountains
Strata: rock layers
Rectangular pattern: forms on igneous rock that has joints and cracks; the streams develop right-angled
bends where joints meet
Centripetal pattern: streams flow into a central pan or low-lying area
Dendritic pattern: has a tree-like appearance; forms on rocks of similar hardness in an area with a similar
gradient
, Parallel pattern: develops on a surface that slopes uniformly but is fairly steep; the river and its tributaries
flow downslope nearly parallel to one another
Deranged pattern: no apparent drainage pattern
Stream order: the category of a stream in a network determined by the order of the streams feeding into it
Discharge: the amount of water flowing in a river channel past a point in a given time – volume of water
flowing through a river channel per unit of time.
Laminar flow: water flowing in sheets/layers; it does not change levels
Turbulent flow: water flowing in a bubbling motion; it changes levels – characterized by chaotic changes in
pressure and flow velocity
