This presentation includes about the rivers and drainage basins.

1. 1
D.G. Nishavi Kaushalya Ranasinghe
B.A. (Hons) Geography
Department of Geography and Environmental Management
Sabaragamuwa University of Sri Lanka

2.  Rivers
 Water cycle
 Drainage basin
 Drainage basin characteristics

3. River
• What is a river?
– A river is a natural flowing watercourse, usually
freshwater, flowing towards an ocean, a lake, a sea,
or another river.
– Small rivers called by several names. Such as,
• Stream
• Creek
• Brook
• Rivulet
• Rill

4. • Rivers receive water from precipitation.
• Precipitation may receive as, rain, hail, snow
and sleet.
Rain Sleet
Hail Snow

5.  There are 04 types of elementary process in a river .
Such as,
◦ From rain water Ex: Mahaweli river
◦ From a spring Ex: Thames river
◦ Melting glaciers Ex: Seine river
◦ From a lake Ex: The Nile river
 Relationship between precipitation and the amount of
water in a river, known as discharge.

6. Stages of River Development
• According to the William Morris Davis (1850 –
1934),
– Flowing water of a river = Life cycle of human
• Mainly there are 03 stages of river
development. As,
1. Youth stage
2. Mature stage
3. Old stage

7. Profile of a river
Long - profile Cross - profile

8. Long – profile of a river

9. River terminology
Characteristic Definition
Width The distance of bank to bank of the surface water of the river
Depth How deep the water in the river.
Velocity The speed at which the river is flowing. This varies with depth
and width.
Wetted perimeter Length of the wet part of the channel cross – section containing
flowing water.
Cross – section
area
Area of the flowing water when measured from bank to bank
Discharge The amount of water flowing in a channel.

10. River A River B

11. The Hydrological Cycle

12. • The hydrological cycle also known as water cycle or H2O
cycle.
• It describes the continuous movement of water on, above
and below the surface of the Earth, contribution of solar
energy.
• The main components of the water cycle can describes
as,
– Evaporation/ Transpiration
– Condensation
– Precipitation
– Run – off
– Infiltration

13. Ways of people change the water cycle
• Deforestation
• Hydroelectricity
• Irrigation
• Urbanization
• Greenhouse effect
• Combustion of fossil fuels
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14. Drainage Basin
• A drainage basin is the catchment area from which a river system
obtains its water.
• It also called catchment, catchment area, catchment basin,
drainage area, river basin and water basin.
• All water that falls on the land flows into one river.
• It can flow directly into the river or go through tributaries first.
• A watershed is a line separating two drainage areas. Also known
as divide.
• What is a drainage basin?

15. • The watershed is usually on the tops of hills and mountains or
high ground.
• Example for drainage basins,
Columbia River drainage basin, the Colorado River basin,
Mississippi River drainage basin in US, Amazon basin

16. Drainage basin features
 Source: the beginning of the river. River
may have multiple sources. The source of
the river is normally found in upland
mountainous area.
 Mouth: the end of the river.
 Tributary: a small river that flows into a
large river.
 Confluence: where two rivers meet.
 Watershed: the boarder between two
drainage basins.
 Channel: the physical confines of the river,
encompassing two banks and a bed.

17. Drainage basin characteristics
1) Drainage patterns
Land is drained by rivers in verity of ways. There are 06 types of
drainage patterns.
 Sub parallel
 Dendritic
 Trellis
 Radial
 Centripetal
 Derranged
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18. 2) Drainage density
this relates to the number of streams in a particular drainage
basin. Can be measured by,
Drainage density (D)=
𝑇𝑜𝑡𝑎𝑙 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑎𝑙𝑙 𝑠𝑡𝑟𝑎𝑚𝑠 𝑖𝑛 𝑏𝑎𝑠𝑖𝑛 (𝐿)
𝐵𝑎𝑠𝑖𝑛 𝑎𝑟𝑒𝑎 (𝐴)
D =
𝐿
𝐴
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19. 3) Stream ordering
With the drainage density in a drainage basin can identify
stream order. As,
1 st order stream
Original source tributaries.
 2 nd order stream
the joining of first two
order streams.
 3 rd order stream
the merging of two second
order streams.
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20. 4) Vegetation factor
These are depended wholly or in part on the vegetation,
natural or cultivated, growing within the drainage – basin.
5) Climatic hydrologic factors.
This include temperature, humidity, rainfall and
evaporation. Hydrologic factors depended on the
operation of the hydrological cycle as well as run off
and underground water.
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