ENVS10001 Lecture 11: Lecture 11 Notes ENVS 10001
17 May 2018
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WATER CYCLE – CLIMATE AND CATCHMENTS
• Water: critical for people – drink, food production (agriculture), health
o Originally people dependent on seasonal cycles for food production
o 50% world’s fresh water used by hydroelectric plants, which loose 10% of what they
process
• Global precipitation ! 1m depth/year, only 75% falls on land
• Water Budget: closed cycle, amount of water on Earth not changing
o Steady state system ! inputs = outputs = 0
Global Stores of Water
• Big stores have long residence time, and
low/slow variability
• Small stores have short residence time, and
high/fast variability
• Groundwater, lakes + rivers ! form our water
supply
Catchment Hydrology
• Catchment: topographically defined area of land in which water flowing over the surface flows
into a particulars stream + eventually through a single point or outlet on that stream/river
• Catchment boundaries determined by contours, streams + catchment outlet
• Amount of water in catchment fluctuates in humid catchments
• Catchments provide runoff via a mix of pathways that have varying response times
Baseflow
• Results from slow seepage of groundwater into a stream ! how flow is maintained in stream
between rainfall events
• Typically reduces overtime as groundwater stores reduce, then increase as groundwater is
replenished during rainfall events
Hillslope Runoff Process
• Infiltration Excess Runoff
o Occurs when rain falls at a rate higher than the rate which soil can absorb the water
" Water not infiltrated becomes runoff
o Controlled by soil surface properties + rainfall intensity
• Saturation Excess Runoff
o Occurs: water table forms in soil + rises to surface, preventing rainfall from infiltration
o Only occurs in wet catchments
• Subsurface Storm Flow
o Occurs under wet conditions on moderate to steep flow, where soil profile has
capacity to deliver high flow rates to the stream
Impacts of Land Use
• Changes catchment surface conditions ! changes infiltration rates
• Changes vegetation ! amount of water evapotranspired
• Changes water supply by irrigation for growing crops
