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Earth Science, 11e Running Water and Groundwater Chapter 5
Earth as a system: the hydrologic cycle Illustrates the circulation of Earth's water supply Processes involved in the cycle Precipitation Evaporation Infiltration Runoff Transpiration
The hydrologic cycle Figure 5.2
Sources of Earth s water Figure 5.1
Running water Drainage basins Land area that contributes water to a river system A divide separates drainage basins
The drainage basin of the Mississippi River Figure 5.3
Running water Streamflow Factors that determine velocity Gradient, or slope Channel characteristics Shape Size Roughness Discharge volume of water flowing in the stream (generally expresses as cubic feet per second)
Running water 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
Running water Upstream-downstream changes Profile Factors that increase downstream Channel size Factors that decrease downstream Gradient, or slope Channel roughness
Longitudinal profile of a stream Figure 5.6
Running water The work of streams Erosion Transportation Transported material is called the stream's load Dissolved load Suspended load Bed load
Running water The work of streams Transportation Load is related to a stream's Competence - maximum particle size Capacity - maximum load Capacity is related to discharge
Running water The work of streams Transportation Deposition Caused by a decrease in velocity Competence is reduced Sediment begins to drop out Stream sediments Known as alluvium Well-sorted deposits
Running water The work of streams Transportation Features produced by deposition Deltas exist in ocean or lakes Natural levees - Form parallel to the stream channel Area behind the levees may contain back swamps or yazoo tributaries
Formation of natural levees by repeated flooding Figure 5.19
Running water Base level Lowest point a stream can erode to Two general types Ultimate sea level Temporary, or local Changing causes readjustment of the stream deposition or erosion
Adjustment of base level to changing conditions Figure 5.13
A waterfall is an example of a local base level
Running water Stream valleys Valley sides are shaped by Weathering Overland flow Mass Wasting Characteristics of narrow valleys V-shaped Downcutting toward base level
Running water Stream valleys Characteristics of narrow valleys 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
A narrow, V-shaped valley Figure 5.15 A
Continued erosion and deposition widens the valley Figure 5.15 B
The resulting wide stream valley is characterized by meandering on a well-developed floodplain Figure 5.15 C
Running water Stream valleys Characteristics of wide valleys Floodplain Features often include Meanders Cutoffs Oxbow lakes
Erosion and deposition along a meandering stream Figure 5.8
A meander loop on the Colorado River
Formation of a cutoff and oxbow lake Figure 5.9
Running water Drainage patterns Networks of streams that from distinctive patterns Types of drainage patterns Dendritic Radial Rectangular Trellis
Drainage patterns Figure 5.20
Running water Floods and flood control Floods are the most common geologic hazard Causes of floods Weather Human interference with the stream system
Running water Floods and flood control Engineering efforts Artificial levees Flood-control dams Channelization Nonstructural approach through sound floodplain management
Satellite view of the Missouri River flowing into the Mississippi River near St. Louis Figure 5.21
Same satellite view during flooding in 1993 Figure 5.21
Water beneath the surface (groundwater) Largest freshwater reservoir for humans Geological roles As an erosional agent, dissolving by groundwater produces Sinkholes Caverns An equalizer of stream flow
Water beneath the surface (groundwater) Distribution and movement of groundwater Distribution of groundwater Belt of soil moisture Zone of aeration Unsaturated zone Pore spaces in the material are filled mainly with air
Water beneath the surface (groundwater) 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
Features associated with subsurface water Figure 5.25
Water beneath the surface (groundwater) Distribution and movement of groundwater Distribution of groundwater Porosity Percentage of pore spaces Determines how much groundwater can be stored Permeability Ability to transmit water through connected pore spaces Aquitard an impermeable layer of material Aquifer a permeable layer of material
Water beneath the surface (groundwater) Features associated with groundwater Springs Hot springs Water is 6-9ºC warmer than the mean air temperature of the locality Heated by cooling of igneous rock Geysers Intermittent hot springs Water turns to steam and erupts
Old Faithful geyser in Yellowstone National Park
Water beneath the surface (groundwater) Features associated with groundwater Wells Pumping can cause a drawdown (lowering) of the water table Pumping can form a cone of depression in the water table Artesian wells Water in the well rises higher than the initial groundwater level
Formation of a cone of depression in the water table Figure 5.30
An artesian well resulting from an inclined aquifer Figure 5.31
Water beneath the surface (groundwater) Environmental problems associated with groundwater Treating it as a nonrenewable resource Land subsidence caused by its withdrawal Contamination
Water beneath the surface (groundwater) Geologic work of 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
Water beneath the surface (groundwater) Geologic work of groundwater Caverns Features found within caverns Form in the zone of aeration Composed of dripstone Calcite deposited as dripping water evaporates Common features include stalactites (hanging from the ceiling) and stalagmites (growing upward from the floor)
Dripstone formations in Carlsbad Caverns National Park
Water beneath the surface (groundwater) Geologic work of groundwater Karst topography Formed by dissolving rock at, or near, Earth's surface Common features Sinkholes surface depressions Sinkholes form by dissolving bedrock and cavern collapse Caves and caverns Area lacks good surface drainage
Features of karst topography Figure 5.37
Infrared image of karst topography in central Florida Figure 5.38 A
End of Chapter 5