Hydrologic cycle
 The
hydrologic cycle is a summary of the circulation of
Earth’s water supply
 Processes involved in the hydrologic cycle
Precipitation
Evaporation
Infiltration
Runoff
Transpiration
Sources of Earth’s water
Running water
 Begins
as sheetflow
Infiltration
capacity is controlled by
 Intensity
and duration of rainfall
wetted condition of the soil
 Soil texture
 Slope of the land
 Nature of the vegetative cover
 Prior
Sheetflow
develops into tiny channels called rills
 Streamflow
Two
types of flow determined primarily by velocity
 Laminar
flow
flow
 Turbulent
 Streamflow
Factors
that determine velocity
 Gradient,
or slope (Rise/Run)
 Channel characteristics including shape, size, and roughness
 Discharge – the volume of water moving past a given point in a certain
amount of time
 Changes
from upstream to downstream
Profile
 Cross-sectional
view of a stream from the head (headwaters or source)
to the mouth of a stream
 Profile is a smooth curve
 Gradient decreases downstream
Longitudinal profile of a stream
Factors
that increase downstream
 Velocity
 Channel
size
 Discharge
Factors
that decrease downstream
 Gradient
 Channel

roughness
Base level and graded streams
 Base
 Two
level is the lowest point to which a stream can erode
general types of base level
 Ultimate
(sea level)
or temporary
 Local
 Changing
conditions causes readjustment of stream activities
 Raising
base level causes deposition
 Lowering base level causes erosion
Adjustment of base level to changing conditions
A waterfall is an example of a local base level
 Stream
erosion
Lifting
loosely consolidated particles by
 Abrasion
 Dissolution
Stronger
 Transport
currents lift particles more effectively
of sediment by streams
Transported
material is called the stream’s load
Types of load
 Dissolved
load
load
 Suspended
 Bed
load
Capacity
– the maximum load a stream can transport
 Competence
Indicates
the maximum particle size a stream can transport
Determined by the stream’s velocity
Increases as the square of velocity
 Deposition
Caused
of sediment by a stream
by a decrease in velocity
 Competence
 Sediment
Stream
is reduced
begins to drop out
sediments
 Generally
 Stream
 Deposition
well sorted
sediments are known as alluvium
of sediment by a stream
Channel
deposits
 Bars
 Braided
streams
 Deltas
Floodplain
deposits
levees – form parallel to the stream channel by successive
floods over many years
 Natural
A Braided Stream
Formation of natural levees by repeated flooding
 Deposition
of sediment by a stream
Floodplain
deposits
 Back
swamps
 Yazoo tributaries
Alluvial
fans
 Develop
where a high-gradient stream leaves a narrow valley
 Slopes outward in a broad arc
Alluvial Fans
 Deposition
of sediment by a stream
Deltas
 Forms
when a stream enters an ocean or lake
of three types of beds
 Foreset beds
 Topset beds
 Bottomset beds
 Consists
The Nile and Mississippi Rivers exhibit different types of deltas
Ancient Delta Foreset Beds
 Stream
valleys
The
most common landforms on Earth’s surface
Two general types of stream valleys
 Narrow
valleys
 V-shaped
 Downcutting
 Features
 Stream
toward base level
often include rapids and waterfalls
valleys
Two
general types of stream valleys
 Wide
valleys
 Stream is near base level
 Downward erosion is less dominant
 Stream
 Stream
energy is directed from side to side forming a floodplain
valleys
Features
of wide valleys often include
 Floodplains
 Erosional
floodplains
floodplains
 Depositional
 Meanders
 Cut
bank and point bar
 Cutoffs and oxbow lakes
Erosion and deposition along
a meandering stream
A Meandering Stream
 Incised
meanders and stream terraces
Incised
meanders
 Meanders
 Caused
in steep, narrow valleys
by a drop in base level or uplift of the region
Terraces
 Remnants
of a former floodplain
 River has adjusted to a relative drop in base level by downcutting
A meander loop on the Colorado River
 Floods
and flood control
Floods
are the most common and most destructive geologic
hazard
Causes of flooding
 Result
 Floods
from naturally occurring and human-induced factors
and flood control
Types
of floods
 Regional
floods
floods
 Ice-jam floods
 Dam failure
 Flash
Satellite view of the Missouri River flowing into the
Mississippi River near St. Louis
Same satellite view during flooding in 1993
 Floods
and flood control
Flood
control
 Engineering
efforts
 Artificial levees
 Flood-control Dams
 Channelization
 Nonstructural approach through sound floodplain management
New Orleans Post Katrina
 Drainage
networks
The
land area that contributes water to a stream is called the
drainage basin
Drainage pattern consists of the interconnected network of
streams in an area
Common drainage patterns
 Dendritic
 Radial
 Rectangular
 Trellis
The drainage basin of the Mississippi River
Drainage patterns
Groundwater Springs
Importance of groundwater
 Groundwater
is water found in the pores of soil and
sediment, plus narrow fractures in bedrock
 Groundwater is the largest reservoir of fresh water that is
readily available to humans
 Geological role of groundwater
As
an erosional agent, dissolving groundwater produces
 Sinkholes
 Caverns
Groundwater
serves as an equalizer of streamflow
Distribution of groundwater
of soil moisture – water held by molecular attraction on
soil particles in the near-surface zone
 Zone of saturation
 Belt
Formation
 Water
 Zone
not held as soil moisture percolates downward
of saturation
Formation
 Water
reaches a zone where all of the open spaces in sediment and rock
are completely filled with water
 Water within the pores is called groundwater
table – the upper limit of the zone of saturation
Water
 Capillary
fringe
Extends
upward from the water table
Groundwater is held by surface tension in tiny passages between
grains of soil or sediment
 Zone
of aeration
Area
above the water table
Includes the capillary fringe and the belt of soil moisture
Water cannot be pumped by wells
Features associated with subsurface water
The water table
 The
water table is the upper limit of the zone of saturation
 Variations in the water table
Depth
is highly variable
 Varies
Shape
seasonably and from year to year
is usually a subdued replica of the surface topography
 Variations
in the water table
Factors
that contribute to the irregular surface of the water
table
 Water
tends to “pile up” beneath high areas
 Variations in rainfall
 Variations in permeability from place to place
 Interaction
between groundwater and streams
Constitutes
a basic link in the hydrologic cycle
Three
types of interactions
or Gaining streams – gain water from the inflow of
groundwater through the streambed
 Influent or Losing streams – lose water to the ground-water system by
outflow through the stream-bed
 A combination of the first two – a stream gains in some sections and
loses in other areas
 Effluent
Gaining and losing streams
Movement of groundwater
 Darcy’s
Law
V = K h/l
gradient – the water table slope, determined by
dividing the vertical difference between the recharge and
discharge points by the length of flow between these points
Hydraulic head – the vertical difference between the recharge
and discharge points
Hydraulic
slow – typical rate of movement is a few
centimeters per day
 Energy for the movement is provided by the force of gravity
 Darcy’s Law – if permeability remains uniform, the velocity
of groundwater will increase as the slope of the water table
increases
 The movement of groundwater is measured directly using
 Exceedingly
Various
dyes
Carbon-14 (decay of naturally occurring C-14)
Factors influencing the storage and movement of
groundwater
– percentage of total volume of rock or sediment
that consists of pore spaces
 Porosity
Determines
how much groundwater can be stored
Variations can be considerable over short distances
 Permeability,
aquitards, and aquifers
– the ability of a material to transmit a fluid
Aquitard – an impermeable layer that hinders or prevents water
movement (such as clay)
Aquifer – permeable rock strata or sediment that transmits
groundwater freely (such as sands and gravels)
Permeability
Features associated with groundwater
 Springs
Occur
where the water table intersects Earth’s surface
Natural outflow of groundwater
Can be caused by an aquitard creating a localized zone of
saturation which is called a perched water table
Springs may result from a perched water table
Features associated with groundwater
 Wells
To
ensure a continuous supply of water, a well must penetrate
below the water table
Pumping of wells can cause
 Drawdown
 Cone
(lowering) of the water table
of depression in the water table
Formation of a cone of depression in the water table
Features associated with groundwater
well – a situation in which groundwater under
pressure rises above the level of the aquifer
 Artesian
Types
of artesian wells
– pressure surface is below ground level
– pressure surface is above the ground
 Nonflowing
 Flowing
Not
all artesian systems are wells, artesian springs also exist
An artesian well resulting from an inclined aquifer
Problems associated with groundwater withdrawal

Treating groundwater as a nonrenewable resource
In many places the water available to recharge the aquifer falls
significantly short of the amount being withdrawn (such as the
Ogallala Sandstone)
 Subsidence
Ground
sinks when water (or oil and water) is pumped from
wells faster than natural recharge processes can replace it (San
Joaquin Valley of California)
Groundwater contamination
 One
common source is sewage
Extremely
permeable aquifers, such as coarse gravel, have such
large openings that groundwater may travel long distances
without being cleaned
Sewage often becomes purified as it passes through a few dozen
meters of an aquifer composed of sand or permeable sandstone
 Sinking a well can lead to groundwater pollution problems
 Other sources and types of contamination include substances such as
 Highway
salt
 Fertilizers
 Pesticides
 Chemical and industrial materials
 Dairies from Los Angeles
Hot springs and geysers
 Hot
springs
is 6-9oC warmer than the mean annual air temperature of
the locality
The water for most hot springs is heated by cooling of igneous
rock
Water
 Geysers
Intermittent
hot springs
Water erupts with great force
Occur where extensive underground chambers exist within hot
igneous rock
Groundwater heats, expands, changes to steam, and erupts
Distribution of hot springs and geysers in the United
States
Old Faithful geyser in Yellowstone National Park
 Geysers
Chemical
sedimentary rock accumulates at the surface
 Siliceous
sinter (from dissolved silica)
 Travertine (from dissolved calcium car-bonate)
Geothermal energy
 Tapping
natural underground reservoirs of steam and hot
water
 Favorable geologic factors include
A
potent source of heat
Large and porous reservoirs with channels connected to the heat
source
A cap of low permeability rocks
 Geothermal
energy is not inexhaustible
The Geysers, a geothermal energy field in California
Geologic work of groundwater
Geologic work of groundwater
 Caverns
Most
caverns are created by acidic groundwater dissolving
soluble rock at or just below the surface in the zone of saturation
Features found within caverns
 They
form in the zone of aeration
 Caverns
Features
found within caverns
 Composed
of dripstone (travertine)
 Calcite deposited as dripping water evaporates
 Collectively, they are called speleothems
 Includes stalactites (hanging from the ceiling) and stalagmites (form
on the floor of a cavern)
Speleothems in Carlsbad Caverns National Park
“Soda straws” in Carlsbad Caverns National Park
Measuring a Cave
 Karst
topography
Landscapes
that to a large extent have been shaped by the
dissolving power of groundwater
Some common features include
 Irregular
terrain
or sinks (formed by groundwater slowly dissolving the
bedrock often accompanied by collapse)
 Striking lack of surface drainage (streams)
 Sinkhole
Development of karst topography
Key Terms Chapter 11
Evaporation, transpiration, condensation, precipitation, sublimation
Runoff, infiltration
Stream
Channel
Gradient
Stream profile
Discharge
Load
Floodplain
Alluvium
Drainage basin, divide
Flood
Groundwater
Water table
Porosity and permeability
Percolation
Recharge and discharge
Spring
Aquifer and aquitard (aquiclude)
Cave
Karst topography
Speleothems (stalactites and stalagmites)