GEOMORPHOLOGY
CHAPTER 1: DRAINAGE SYSTEMS IN SOUTH AFRICA
IMPORTANT CONCEPTS
Drainage basin – entire area drained by a river and its tributaries
Watersheds – ridge of high land that separates two drainage basins
Interfluves – the area of higher ground separating tributaries
Catchment area – refers to all water in the drainage basin: both ground and
surface water
Tributaries – smaller rivers joining main river
Confluence point – point where the tributary joins the main river
Porosity – number of holes in rock
Permeability – ability of rock to allow water to pass through
Source – start of the river
o high mountainous area
o may develop at a spring
o may be result of meltwater
o may be the point furthest away from where it joins another river
Mouth – end of the river
o Point where river enters sea or other large body of water
o Deposition
o Delta or estuary
Water table – the upper level of groundwater
Surface water:
o Flows on the earth’s surface
o Remains after losses through evaporation, infiltration and surface retention
o Initially flows as sheetwash/sheet flow
o Direct runoff
Ground water:
o Infiltrates into earth’s surface
o Occurs in rocks that allow water infiltration aquifers
o Collects in cracks and pores of the earth’s crust
o Gravity forces water deeper into crust
o Indirect runoff
o Soil water – water that infiltrates soil
o Zone of intermittent saturation – pore space is filled up with both air
and water
o Zone of intermittent saturation – all pore space is filled with water
Water table will:
o Rise after high rainfall & drop in drought
o May intersect with earth’s surface at bottom of river baseflow
o May intersect with earth’s surface on side of hill spring
Factors influencing infiltration:
o Precipitation – greater rain and or soft soaking rain greater infiltration
o Evaporation – dry, hot and windy more evaporation lesser
infiltration
o Gradient – steeper rapid runoff lesser infiltration
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, o Vegetation – runoff is trapped by vegetation/shade (less evap.)
infiltration decreased
o Moisture in soil – saturated soil cannot absorb water lesser infiltration
o Porosity & permeability – if rock is both porous and permeable
greater infiltration
2|Page
CHAPTER 1: DRAINAGE SYSTEMS IN SOUTH AFRICA
IMPORTANT CONCEPTS
Drainage basin – entire area drained by a river and its tributaries
Watersheds – ridge of high land that separates two drainage basins
Interfluves – the area of higher ground separating tributaries
Catchment area – refers to all water in the drainage basin: both ground and
surface water
Tributaries – smaller rivers joining main river
Confluence point – point where the tributary joins the main river
Porosity – number of holes in rock
Permeability – ability of rock to allow water to pass through
Source – start of the river
o high mountainous area
o may develop at a spring
o may be result of meltwater
o may be the point furthest away from where it joins another river
Mouth – end of the river
o Point where river enters sea or other large body of water
o Deposition
o Delta or estuary
Water table – the upper level of groundwater
Surface water:
o Flows on the earth’s surface
o Remains after losses through evaporation, infiltration and surface retention
o Initially flows as sheetwash/sheet flow
o Direct runoff
Ground water:
o Infiltrates into earth’s surface
o Occurs in rocks that allow water infiltration aquifers
o Collects in cracks and pores of the earth’s crust
o Gravity forces water deeper into crust
o Indirect runoff
o Soil water – water that infiltrates soil
o Zone of intermittent saturation – pore space is filled up with both air
and water
o Zone of intermittent saturation – all pore space is filled with water
Water table will:
o Rise after high rainfall & drop in drought
o May intersect with earth’s surface at bottom of river baseflow
o May intersect with earth’s surface on side of hill spring
Factors influencing infiltration:
o Precipitation – greater rain and or soft soaking rain greater infiltration
o Evaporation – dry, hot and windy more evaporation lesser
infiltration
o Gradient – steeper rapid runoff lesser infiltration
1|Page
, o Vegetation – runoff is trapped by vegetation/shade (less evap.)
infiltration decreased
o Moisture in soil – saturated soil cannot absorb water lesser infiltration
o Porosity & permeability – if rock is both porous and permeable
greater infiltration
2|Page
