Option A: Freshwater — Drainage basins 3
A.1 Drainage basin hydrology & geomorphology 3
The drainage basin 3
Definitions 3
Flows: 3
Stores: 4
River discharge 5
The main types of erosion: 5
Factors affecting erosion: 5
Transportation: 5
Theory of channel load: 6
Temporal variations in processes: River landforms 6
River regime 6
Deposition 6
Floodplains 6
Levees 6
Waterfalls 7
Meanders 7
Deltas 7
A.2 Flooding & flood mitigation 8
Hydrographs 8
Land-use change and flood risk 9
Urbanisation 9
Deforestation 9
Channel modifications 10
Flood prediction and mitigation 10
Flood warnings and preparation 10
Floodplain zoning 11
Flood control - protective measures along flood channels 11
Dams and reservoirs 11
River straightening and dredging 12
Embankments 12
Flood relief channels 12
Two contrasting detailed examples of flood mitigation of drainage basins 13
Flood mitigation in Pakistan: 13
Flood mitigation in Queensland, Australia: 13
A.3 Water scarcity & water quality 13
Water scarcity 13
Environmental impacts of agricultural activities 15
Case study: Jordan Lake — US 15
Human pressures on lakes and aquifers 16
Internationally shared water resources 16
A source of conflict: 16
1
, The Grand Ethiopian Renaissance Dam 16
A.4 Water management futures 17
Increased dam building 17
Case study: The Three Gorges Dam — China 17
Integrated drainage basin management (IDBM) 18
Example: Costa Rica 19
Wetlands 19
Ramsar convention 19
The value of wetlands 19
Loss & degradation 20
Case study: Changing river management - the Kissimmee River (Florida) 20
Community participation 21
Water supply 21
Sustainable Water Management 21
Case Study: Singapore 22
2
, Option A: Freshwater — Drainage basins
A.1 Drainage basin hydrology & geomorphology
The drainage basin
Hydrology: the study of water
→ water cycle, water resources, and environmental watershed sustainability.
Geomorphology: the study of the earth
→ Geomorphologists seek to understand why landscapes look the way they do, to
understand landform and terrain history and dynamics and to predict changes.
Definitions
→ has inputs, stores, processes and outputs
● inputs and outputs cross the boundary of the drainage basin → open system
● main input of the system:
○ Precipitation: Any moisture that falls from the sky e.g. rain or snow
● outputs include: evaporation ✗ transpiration
○ Evaporation: liquid water from surface stores and rivers turning into water
vapour
○ Transpiration: liquid water evaporating from vegetation
○ Evapotranspiration: combined loss of water from vegetation and water
surfaces to the atmosphere
Open System: is a system that transfers
energy, but not matter across its boundary to
the surrounding environment.
Closed system: is a system that transfers
both matter and energy across its boundary
to the surrounding environment.
Drainage Basin: an area that is drained by a
river and its tributaries
Flows:
Infiltration: When water travels from the surface of the earth into the ground beneath.
Throughflow: The movement of water through unsaturated ground.
Surface run-off (overland flow): When water travels across the surface of the earth
Percolation: When water travels from unsaturated ground into saturated ground.
River discharge: Eventually most rivers enter the sea and discharge the river's flow into the
3
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