GEOL102.24p-Topic4_Surface_Water.pdf

Kakabeka Falls near Thunder Bay, Ontario. Source: Joyce McBeth (2008) CC BY 4.0 Topic 4: The Hydrologic Cycle - Surface Water Why is Water Important?
covers ~70% of Earth’s surface
essential to life on Earth
key role in Earth's climate system: heat regulation, distribution...

Kakabeka Falls near Thunder Bay, Ontario. Source: Joyce McBeth (2008) CC BY 4.0 Topic 4: The Hydrologic Cycle - Surface Water Why is Water Important?
covers ~70% of Earth’s surface
essential to life on Earth
key role in Earth's climate system: heat regulation, distribution
critical to society: used in industry, agriculture, domestic use, etc.
it is a renewable resource Source: NASA, http://visibleearth.nasa.gov/  Water on Earth
97% in oceans, 3% fresh water
only 1% of fresh water is easily accessible (i.e. surface water) - most is tied up in glaciers, groundwater
only ~50% of easily accessible fresh water is in lakes and rivers Source: www.australianenvironmentaleducation.com
Canada has ~6.6% of world's fresh water reserves (ranked 3rd globally) Hydrologic Cycle
water at Earth’s surface can exist in any of the three states of matter: - liquid (water) - solid (ice) - gas (water vapour)
transformations between these: - drives fluxes between reservoirs (e.g. ocean and atmosphere) - are temperature-dependent (e.g. evaporation rates of water are faster at higher temperatures) "flux" = flow rate, rate of transfer between reservoirs Hydrologic Cycle Precipitation runs off Excess falls on land into lakes, streams, Flux in and flux out over as precipitation and oceans… oceans is almost balanced …or infiltrates into soil and rock, where it moves as groundwater Units: 103 km3/year Precipitation
water vapour condenses into droplets
droplets coalesce into larger droplets and fall (as rain or snow)
responsible for majority of fresh water on Earth Photo by CLS Research Office Major Water Reservoirs on Earth
most significant reservoirs: - oceans (97%) - glaciers (2.1%) - groundwater (0.9%) Source: Steven Earle (2015) CC BY 4.0, data from USGS Water Science School (2016) Residence Time
a reservoir: - contains a defined volume of water - water can be added or removed over time
the average length of time that a water molecule will remain in reservoir at or near a steady-state condition  



 
   
 
  

  

  
 
e.g. glass contains 300 mL of water  rate of removal or addition is 30 mL/s, so residence time is 10 s
unit conversion: 1 m3 = 1000 L Major Reservoirs - residence times
essential to consider long-term effects and impact of pollutants entering our water systems Influence of Dams
have many societal benefits  renewable energy supply, source of fresh water, flood protection, water security
also have environmental & societal impacts
dam & reservoir  flooding of large areas; higher evaporation rates; impacts fish migration; can displace human communities Source: Fletcher et al (2014) Intro. to Physical Geology, Wiley.
downstream of dam  river is deprived of sediment, erodes into its bed; river and lands may become less fertile
upstream of dam  river loses energy - sediment deposition and accumulation reduces reservoir volume - can reduce lifespan up to 50%  Fresh Water
small proportion of all water is accessible for human use - ~99% of all liquid water is seawater - much of it is not renewable on human timescales
desalination can produce small amounts of fresh water from sea water  BUT highly energy-intensive and very expensive at an industrial scale
unsustainable use of fresh water risks long-term water availability - excessive extraction for industrial use, domestic use, and irrigation - contamination of surface and groundwater  The majority of surface water in Canada drains to the Arctic, so is not available to most Canadians (85% of population lives within 300 km of U.S. border) a ad an C Data from www.woldwater.org 2011, drawing by Steven Earle Water Use by Sector
in Canada, most water is used for energy generation and industrial purposes Source: Fletcher et al (2014) Intro. to Physical Geology, Wiley.
usage can vary widely from country to country Freshwater Availability
to avoid stressing the water supply, water supply should be at least 10x the average use per day
"water stress"  when a region withdraws 25% or more of its renewable freshwater resources
"water scarcity"  demand for water exceeds available supply Global Water Scarcity
2/3 of the global population (~4 billion people) live under conditions of severe water scarcity at least 1 month of the year
half a billion people in the world face severe water scarcity all year round Data: 1995-2005. Source: Mekonnen et al (2016) Science Advances  "arid" = describes climate Droughts conditions with little to no rain, e.g. in deserts
prolonged shortage in water supply, e.g. precipitation substantially below normal for months to years - streams, wetlands, and lakes dry up - groundwater levels decline
arid regions most susceptible, but can occur in all climates - impacts availability of water for drinking and irrigation
recent / ongoing droughts: - Sahel region of Africa - western USA theconversation.com  Future of Water?
NASA satellite data over 15 years (2002 to 2017) show regions losing (red) or gaining (blue) fresh water
deeply troubling Source: Famiglietti (2019), www. - why? pewtrusts.org
global tropics are getting wetter, but mid-latitude regions getting drier ("wet getting wetter, and dry getting drier")
red hotspots: (1) melting glaciers and ice sheets, (2) places where groundwater being withdrawn (for irrigation) faster than it can be replenished (e.g. Bangladesh, India, China) (3) intensifying drought- stricken areas (e.g. Texas, Brazil, Caspian Sea) Summary – Surface Water
importance of water and water on earth
hydrologic cycle - major reservoirs and fluxes between them
residence time - avg. length of time a water molecule remains
influence of dams
fresh water - global resources, use by sector, availability (stress, scarcity), the future of water  Note: This course will not Suggested Readings cover all of the material in each chapter of the Textbook textbook. These reading recommendations highlight Chapter 14 material relevant to this course.
Introduction
Section 14.1: The hydrological cycle
Section 14.2: Drainage basins
Section 14.3: Stream erosion and deposition Workbook Chapter 14 - vocabulary and review questions Additional Materials: Surface Water Surface Water and Its Treatment - this short video discusses methods of storing surface water, the natural and human activity which can affect water quality, and what can be done to ensure we have a clean and safe source of fresh water.