Geomorphology
River systems
- Drainage systems
- a number of small streams and rivers join to form a river system
- a river - body of water flowing down slope in a defined channel from a source
to mouth
Drainage basin and catchment area
- Drainage basin - area drained by a river system or stream network
- catchment area - drainage area that supplies water to a river
- Catchment area supplies underground water that seeps into the river
- catchment area - not always same size as drainage basin, it is determined
by the origin of underground water
Precipitation in drainage basin
- Drainage basin - an open system of input, stores, close and outputs
- Drainage basin - collects precipitation, allows water to infiltrate or seep
underground to become groundwater, stores water in lakes, in Wetlands and
Underground.
- rainwater that does not infiltrate underground flows over surface as surface
runoff
- runoff flows into streams that join main river that flow out of Basin
- eventually water flows into ocean when the river reaches level
- precipitation that does not infiltrate underground or floods over surface may
evaporate, intercepted by vegetation or be transpired as water vapour.
Features of drainage basin - watershed, tributary, river mouth, source &
confluence
- drainage basin has several features
- high ground separating one drainage basin from adjacent drainage
basin is called watershed
- within the drainage basin, individual streams and river channels join
together to form stream or river network
- individual river channels that form the stream network are called
tributaries
- the confluence is the point where one river in the River network joins
another
- interfluve or Spurs are ridges of high ground between individual
channels of the stream network
- the place where a stream or river begins is called the source…
usually in mountainous terrain where the precipitation flowing over land
erodes a small channel
, Vocab
- Surface runoff - rainwater flowing over the surface
- Watershed - high ground separating one drainage basin from the adjacent
drainage basin
- Stream or river network - individual streams and river channels forming the
stream network
- Tributaries - individual river channels forming the stream network
- Confluence - point where one river in the network joins another
- Interfluves - ridges of high ground between individuals
Important watersheds in South Africa
- Drakensberg mountains : the high ground that separates the rivers that flow
down eastern plateau slopes into the Indian ocean from the orange river.
- Witwatersrand : the high ground separating the limpopo river system, flows
northwards and then eastwards
Surface runoff and groundwater
- Large amounts of rainwater may flow over the surface as surface runoff or
overland flow.
- Surface runoff erodes small streams that eventually join together forming
wider, deeper channels in which water flows as channel flow
- Rainwater may also infiltrate and flow through the soil as throughflow.
, - Water may percolate into permeable rocks underground and become
groundwater (or underground water), which flows through these underground
rocks as groundwater flow.
Factors that influence amount of water that enters the drainage basin will
become surface runoff, how much will infiltrate underground
- Relief : more surface runoff if gradient = steep, water flows down steep
gradient quickly, there is less time for water to infiltrate
- Soil type : there will be greater amounts of surface runoff if the soil is thin and
not porous, as no water will be able to infiltrate the soil
- Rock type : there will be greater amounts of surface runoff if the rock is
impermeable, no water will be able to infiltrate and percolate through the
rocks
- Soil moisture : there will be greater amounts of surface runoff if the soil is
saturated and cannot absorb any more water
- Vegetation : greater surface runoff = where little vegetation, veg intercepts
precipitation and allows infiltration
- Rainfall : heavy storms = more surface runoff, water flows quickly over land
- Land use : there is much runoff in urban areas, concrete + tar surface =
impermeable
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