Information about water

1. Chapter 9 Lecture
© 2015 Pearson Education, Inc.
Water
Resources
Geosystems
9th Edition

2. © 2015 Pearson Education, Inc.
Learning Objectives
• Illustrate the hydrologic cycle with a simple sketch, and
label it with definitions for each water pathway.
• Discuss water storage in lakes and wetlands
• Describe the nature of groundwater, and define the
elements of the groundwater environment.

3. © 2015 Pearson Education, Inc.
Hydrologic Cycle
• The hydrologic cycle has operated for billions of
years from the lower atmosphere to several
kilometers beneath Earth’s surface.
• It circulates through the lithosphere, biosphere,
hydrosphere and atmosphere.
• Video: The water cycle

4. © 2015 Pearson Education, Inc.
Hydrologic Cycle

5. © 2015 Pearson Education, Inc.
Hydrologic Cycle
• Water moves the hydrologic cycle in the following ways:
– Precipitation
– Evaporation
– Transpiration
– Evapotranspiration
– Interception
– Infiltration
– Overland flow
– Surface run-off
– Stream flow
– Percolation
– Soil moisture

6. © 2015 Pearson Education, Inc.
Water in the Atmosphere
• Evaporation
– The net movement of free water molecules away from
a wet surface into air that is less saturated
• Transpiration
– Plants release water to the atmosphere through small
openings called stomata in their leaves
• Evapotranspiration
– is a collective term (evaporation + transpiration) for all
the processes by which water in the liquid or solid
phase at or near the land surface becomes water
vapor.
• Stream flow
– Water joins streams and rivers

7. © 2015 Pearson Education, Inc.
Water at the surface
• Precipitation that reaches Earth’s surface as rain
follows two basic pathways:
– either flows overland or soaks into the soil.
– Precipitation can be in the form of a solid (snow, hail, sleet),
liquid (rain) and gas (water vapour, fog)
• Along the way interception also occurs, in which
precipitation lands on vegetation or other ground cover
before reaching the surface.
• Infiltration - When precipitation soaks into the soil and
percolates into the ground
• If the ground is impermeable, water will begin to flow
downslope as overland flow, or surface run-off. This
can also occur if the soil is saturated.

8. © 2015 Pearson Education, Inc.
Surface Water Resources
• Humans require a steady source of water, we rely on
large-scale management projects to redistribute or store
water until it is needed.
• Which large scale water projects do we find in South
Africa?
• Is our water management sufficient?
• Fresh water on the Earth’s surface is found primarily in
snow and ice, rivers, lakes and wetlands.
• Video: Water quality in SA

9. © 2015 Pearson Education, Inc.
Water storage
• Largest amount of freshwater is stored in glaciers,
permafrost and polar ice.
• Seasonal snow and glacial melt feed stream flow.
• Glaciers provide semi-permanent form of water storage.
• Glacial melt has been accelerated due to rising
temperatures associated with climate change.
• Surface runoff and base flow from groundwater move
across the Earth’s surface in rivers and streams.
• Freshwater lakes are fed by precipitation, streamflow,
and groundwater and store about 125 000 km² of
freshwater on Earth’s surface.
• Other than ice sheets and glaciers, the largest repository
of fresh water is located in groundwater.

10. © 2015 Pearson Education, Inc.
Surface Water

11. © 2015 Pearson Education, Inc.
Water in the subsurface
• Water that infiltrates into the subsurface moves
downward into soil or rock by percolation, the slow
passage of water through a porous substance.
• Soil moisture zone contains the volume of sub-surface
water stored in the soil that is accessible to plant roots.
• The soil moisture content indicates the amount of
water present in the soil.

12. © 2015 Pearson Education, Inc.
Types of Soil Moisture
• Hygroscopic water forms as a very thin film surrounding
soil particles and is generally not available to the plant.
– This type of soil water is bound so tightly to the soil by
adhesion properties that very little of it can be taken
up by plant roots.
• Capillary water is water held in the micropores of the
soil due to surface tension properties (cohesion and
adhesion are stronger than the force of gravity.
– It is the main water that is available to plants as it is trapped in
the soil solution right next to the roots if the plant
• Gravitational water is free water moving through soil by
the force of gravity. It is unavailable to plants as it drains
rapidly down the water table.

13. © 2015 Pearson Education, Inc.
Types of Soil Moisture

14. © 2015 Pearson Education, Inc.
Types of Soil Moisture
• Wilting point - If no additional water is supplied to the
soil, it gradually dries out.
– The soil water content at the stage where the plant dies, is called
wilting point. The soil still contains some water, but it is too
difficult for the roots to suck it from the soil
• Field capacity is the limit of available water for plants.
The moisture condition favours higher absorption of
water and nutrients by the plants.
• Saturation point is if all the soil pores are filled with
water. Plants need air and water in the soil. At
saturation, no air is present and the plant will suffer.
• Video: Soil moisture

15. © 2015 Pearson Education, Inc.
Wetlands
• A wetland is an area that is permanently or seasonally
saturated with water and characterized by vegetation
adapted to hydric soils (anaerobic or without O).
• The water can be freshwater or saltwater.
• Large wetlands are NB sources of freshwater and
recharge groundwater supplies.
• Wetlands mitigate flood damage as they absorb and
spread out floodwaters.
• Wetlands improve water quality by trapping sediment
and removing nutrients and pollutants.
• Video: Wetlands

16. © 2015 Pearson Education, Inc.
Groundwater Resources
• Groundwater is supplied by surface water
• 700 km3/year groundwater extracted by people
• Most used for irrigation and drinking water
• Clean
• Not affected by short-term drought
• Groundwater lies beneath the surface beyond the soil
moisture root zone.
• Excess surface water moves through the zone of
aeration, where soil is not saturated.
• Eventually, the water reaches the saturation zone.
• The upper limit of the water that collects in the
saturation zone is the water table

17. © 2015 Pearson Education, Inc.
Groundwater Resources (Aquifers)
• An aquifer is a rock layer that is permeable to
groundwater flow in usable amounts.
• An unconfined aquifer has a permeable layer on top
and an impermeable one beneath.
• A confined aquifer is bounded above and below by
impermeable layers of rock or unconsolidated material.
• A confined aquifer is bounded above and below by
impermeable layers (aquiclude).
• Aquiclude is an impermeable body of rock.
• An artesian aquifer (well), is a confined aquifer
containing groundwater that will flow upward through a
well without the need for pumping.
• Water table is the upper limit of the saturation zone.

18. © 2015 Pearson Education, Inc.
Unconfined Aquifer

19. © 2015 Pearson Education, Inc.
Groundwater Emerging at the Surface:
Springs
Groundwater
moves from areas
of higher pressure
and elevation
toward areas of
lower pressure
and elevation.

20. © 2015 Pearson Education, Inc.
Groundwater and Streamflow

21. © 2015 Pearson Education, Inc.
Groundwater and Streamflow
• Effluent conditions: Water table is higher than
the stream channel.
– Effluent streams tend to be perennial (all year).
• Influent conditions: Water table is lower than
the stream channel.
– Influent streams may be intermittent or ephemeral
(flow only part of the year).

22. © 2015 Pearson Education, Inc.

23. © 2015 Pearson Education, Inc.
• Over-pumping
• Collapsing aquifers
• Saltwater intrusion
Overuse of Groundwater

24. © 2015 Pearson Education, Inc.
Our Water Supply

25. © 2015 Pearson Education, Inc.
Summary of Chapter 9
• Water molecules came from within Earth over a period of billions of years in the
outgassing process. Water covers about 71% of Earth. Approximately 97% of it is
salty seawater, and the remaining 3% is freshwater—most of it frozen.
• The hydrologic cycle is a model of Earth’s water system, which has operated for
billions of years from the lower atmosphere to several kilometers beneath Earth’s
surface. Evaporation is the net movement of free water molecules away from a
wet surface into air. Transpiration is the movement of water through plants and
back into the atmosphere. Evaporation and transpiration are combined into one
term—evapotranspiration.
• A water budget can be established for any area of Earth’s surface by measuring
the precipitation input and the output of various water demands in the area
considered. If demands are met and extra water remains, a surplus occurs. If
demand exceeds supply, a deficit results.
• Groundwater lies beneath the surface beyond the soil moisture root zone. Excess
surface water moves through the zone of aeration, where soil is not saturated.
Eventually, the water reaches the saturation zone. The upper limit of the water
that collects in the saturation zone is the water table.
• An aquifer is a rock layer that is permeable to groundwater flow in usable
amounts. An unconfined aquifer has a permeable layer on top and an
impermeable one beneath. A confined aquifer is bounded above and below by
impermeable layers of rock or unconsolidated material.

26. © 2015 Pearson Education, Inc.
End of Chapter 9