GLG 110
Part 3
Chapter 10
Water: Process, Supply, and Use
Water
is the most important natural resource
70%
of water is used in agriculture
20%
of water is used in industry
10%
of water is used in residences
Water
resources are being diminished worldwide!
10.1
Water: A Brief Global Perspective
The hydrologic cycle illustrated the movement of water on
Earth (Fig. 10.1)
Globally, water is abundant, but locally, water shortages exist
99% of water is salt water in the oceans, unavailable to humans
Water use per capita in the
10.2
Water as a Unique Liquid
Unique liquid, without it life as we know it would be impossible
Covalent bonding of 2 hydrogen atoms and one oxygen atom
Hydrogen end on molecule is more positively charged than the oxygen side
(dipolar molecule)
Because of dipolar nature of water: cohesion of molecules (film of water) and
Adhesion (attraction to solid surfaces), and surface tension
Water is universal solvent
Water in its sold form (ice) is lighter than the liquid
Water’s triple point: exists on or near Earth surface (00 C)
Specific heat of water: 1.0 calorie/g (heat needed to raise temp. of one gram
one degree Celsius); water has great capacity to store and absorb heat
10.3
Surface Runoff and Sediment Yield
Runoff has important effects on erosion and transport of materials
Water moves materials in three ways:
Dissolved, suspended, or by bed load (rolling, jumping)
Flow of water is divided by watersheds (drainage basins) (Fig 10.3)
Factors
Affecting Runoff
Geologic Factors:
Rock and soil type, mineralogy, degree of weathering, structural
characteristics
Physiographic Factors:
Shape of the drainage basin, relief and slope, orientation of the stream
basin
Climatic Factors:
Type of precipitation, intensity of precipitation, duration of precipitation,
types of storms
Biologic Factors:
Vegetation, animals, and soil organisms
Runoff
Paths
Through flow: shallow subsurface flow above the groundwater level
Overland flow: runoff on the surface
Groundwater flow: see next section
Sediment
Yield (volume or mass of sediment per unit time)
Smaller basins tend to yield more sediment than larger basins
10.4
Groundwater (Fig. 10.6)
Vadose zone: formerly called the unsaturated zone (pore space not completely
filled with water)
Zone of saturation: groundwater with water flowing within it
Water table: upper surface of zone of saturation
Capillary fringe: just above the water table, water is drawn up by capillary
action
Aquifers:
zone of earth material capable of supplying groundwater at a useful rate from a
well (Fig. 10.7 b)
Aquiclude (aquitard): confining layer through which little water moves
Unconfined aquifer: aquifer without a confining layer above it
Confined aquifer: aquifer with confining layer above it; results in artesian
wells
Cone of depression: depression in the water table due to pumping from well
(Fig. 10.10)
Groundwater
Movement: dependent on gradient of water table and materials in ground
Porosity: percent of void space in soil or rock
Permeability: ability of material to transmit fluids
Interactions
Between Surface Water and Groundwater (Figs. 10.9 and 10.11)
Effluent river: groundwater seeps into channel, maintaining flow year round
Influent river: channel is above groundwater table, dry out in summer
Perceptions
About Groundwater:
Water is always available whenever we turn on the faucet
Groundwater is “Out of sight, out of mind”
Groundwater is not easily measured, we rely on estimates of probable reserves
10.5
Water Supply
Water supply depends on: precipitation, evaporation, stream flow, subsurface
flow
Here we will look at the
The
Water Budget:
The input, output, and storage of water
For the
The
Groundwater Supply:
Half of the population uses groundwater
20% of water withdrawn comes from groundwater
Over-pumping groundwater causes serious problems in some parts of the country
Desalination:
A very expensive way of obtaining water
Not feasible for most communities
10.6
Water Use
Offstream use: removal of water from its source
Uses include: irrigation, industry, public supply
Consumptive use: offstream use which does not return water to the stream or
groundwater (used by animals and plants, evaporation)
Instream use: water used but not withdrawn from source (e.g. navigation,
hydroelectric power, fish and wildlife, recreation)
Water use diagram see Fig. 10.15
Movement
of Water to People
Metro areas demand large quantities of water
Price of water is often kept low by government agencies
Ways to import water include large diversion projects (e.g. Central Valley
Project, CA;
Trends
in Water Use
Surface water withdrawal exceeds groundwater withdrawal
Water withdrawal increased until the 1980’s and has since leveled off
Better water conservation and management practices
Biggest users are thermoelectric industry and agriculture
Residential use of water has increased due to increase in population
Agricultural use of water has leveled off due to water conservation efforts
Water
Conservation
Practices include:
Covered canals for water transport
Computer monitoring and scheduling of water release from canals
More integrated use of surface water and groundwater
Night irrigation
Improved irrigation systems (e.g. sprinklers, drip irrigation)
Better land preparation for water application
10.7
Water management
Management is complex and includes: locating alternative supplies, better
managing existing supplies, and controlling growth
The
Future of Water Management
A new philosophy of water management is needed!
Water may be traded like oil or gas in the future
A
managed River: The Colorado
See Fig. 10.19 and Table 10.7
10.8
Dams, Reservoirs, and Canals
Many problems arise with construction of these water management devises
Dams
and Reservoirs
They are multipurpose structures (flood control, recreation, water supply,
hydroelectric power)
Canals
They tend to lose water by evaporation, infiltration (unlined canals), and may
be the breeding ground for diseases
10.9
Water and Ecosystems
Humans are degrading many ecosystems
Hydrology is an important part of many ecosystems
Study
questions are on page 290.