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2 Changing urban systems
106
3 Urban environmental and social stresses
110
4 Building sustainable urban systems for the future 114
OPTION A FRESHWATER – DRAINAGE BASINS
1
DRAINAGE BASIN HYDROLOGY AND GEOMORPHOLOGY
The drainage basin
Evaporation is the physical process by which a liquid
becomes a gas. It is a function of:
The drainage basin is an area that is drained by a river
• vapour pressure
and its tributaries. Drainage basins have inputs, stores,
• air temperature
processes and outputs. The inputs and outputs cross the
• wind
boundary of the drainage basin, hence the drainage basin
• rock surface, for example, bare soils and rocks have
is an open system. The main input is precipitation, which is
high rates of evaporation compared with surfaces
regulated by various means of storage. The outputs include
which have a protective tilth where rates are low.
evaporation and transpiration. Flows include in ltration,
through ow, overland ow and base ow, and stores
Transpiration is the loss of water from vegetation.
include vegetation, soil, aquifers and the cryosphere (snow Evapotranspiration is the combined loss of water
and ice).
from vegetation and water surfaces to the atmosphere.
Drainage basin hydrology
Potential evapotranspiration is the rate of water loss
from an area if there were no shortage of water.
PRECIPITATION
DEFINITIONS
Channel
precipitation
Interception
FLOWS
1.VEGETATION
Stemflow &
throughfall
Floods
5. CH
STOR
2. SURFACE
Overland flow
In ltration is the process by which water sinks into the
ground. In ltration capacity refers to the amount of
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