Chapter Four: Running Water and Groundwater
Chapter Objective:
Chapter Outline
Hydrologic cycle
Illustrates the circulation of Earth's water supply
Processes involved in the cycle
Precipitation
Evaporation
Infiltration
Runoff
Transpiration
Cycle is balanced
Running water
Streamflow
Factors that determine velocity
Gradient, or slope
Channel characteristics
Shape
Size
Roughness
Discharge
Upstream-downstream changes
Profile
Cross-sectional view of a stream
From head (source) to mouth
Profile is a smooth curve
Gradient decreases from the head to the mouth
Factors that increase downstream
Velocity
Discharge
Channel size
Factors that decrease downstream
Gradient, or slope
Channel roughness
Base level
Lowest point a stream can erode to
Two general types
Ultimate
Temporary, or local
Changing causes readjustment of the stream
Work
of
streams
Erosion
Transportation
Transported material is called the stream's load
Types of load
Dissolved load
Suspended load
Bed load
Load is related to a stream's
Competence
Maximum particle size
Determined by velocity
Capacity
Maximum load
Related to discharge
Deposition
Caused by a decrease in velocity
Competence is reduced
Sediment begins to drop out
Stream sediments
Called alluvium
Well-sorted deposits
Features produced by deposition
DeltasExists in oceans or lakes
Disturbances often form in channel
Natural levees
Form parallel to the stream channel
Area behind the levees may contain
Back swamps
Yazoo tributaries
Stream valleys
Valley sides are shaped by
Weathering
Overland flow
Mass wasting
Characteristics of narrow valleys
V-shaped
Downcutting toward base level
Features often include
Rapids
Waterfalls
Characteristics of wide valleys
Stream is near base level
Downward erosion is less dominant
Stream energy is directed from side-to-side
Floodplain
Features often include
Meanders
Cutoffs
Oxbow lakes
Drainage basins and patterns
A divide separates drainage basins
Types of drainage patterns
Dendritic
Radial
Rectangular
Trellis
Stages of valley development
Youth
Rapids and waterfalls
V-shaped valleys
Vigorous downcutting
Steep gradient
Maturity
Downward erosion diminishes
Lateral erosion dominates
Floodplain beginning
Gradient lower than at youth
Old age
Large floodplain
Widespread shifting of the stream
Characteristic features
Natural levees
Backswamps
Yazoo tributaries
Rejuvenation
" Made young again "
Characteristic features
Entrenched meanders
Terraces
Water beneath the surface (groundwater)
Largest freshwater reservoir for humansGeological roles
As an erosional agent, dissolving by groundwater produces
Sinkholes
Caverns
An equalizer of streamflow
Distribution and movement of groundwater
Distribution of groundwater
Zone of saturation
All pore spaces in the material are filled with water
Water within the pores is groundwater
Water table - the upper limit of the zone of saturation
Zone aeration
Area above the water table
Pore spaces in the material are filled mainly with air
Movement of groundwater
Porosity
Percentage of pore spaces
Determines how much groundwater can be stored
Permeability
Ability to transmit water through connected pore spaces
Aquiclude - an impermeable layer of material
Aquifer - a permeable layer of material
Water features
Springs
Hot springs
Water is 6-9 degrees C warmer than the mean air temperature of the locality
Heated by cooling
of igneous rockGeysers
Intermittent hot springs
Water turns to steam and erupts
WELLS
Pumping can cause a drawdown (lowering)of the watertable
Pumping can form a cone of depression in the water table
Artesian wells
Water in the well rises higher than the initial groundwater level
Types of artesian wells
Non flowing
Flowing
Environmental problems associated with groundwater
Treating it as a nonrenewable resource
Land subsidence caused by its withdrawal
Contamination
Features produced by groundwater
Groundwater is often mildly acidic
Contains weak carbonic acid
Dissolves calcite in limestone
Caverns
Formed by dissolving rock beneath Earth's surface
Formed in the zone of saturation
Features found within caverns
Form in the zone of aeration
Composed of dripstone
Calcite deposited as dripping water evaporates
Common features
Stalactites hanging from the ceiling
Stalagmites developing on the cave floor
Karst topography
Formed by dissolving rock at, or near, Earth's surface
Common Features
Sinkholes
Surface depressions
Formed by
Dissolving bedrock
Cavern collapse
Cave and Caverns
Area lacks good surface drainage
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