Chapter 16: Running Water. Hydrologic cycle The hydrologic cycle is a summary of the circulation of...
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Transcript of Chapter 16: Running Water. Hydrologic cycle The hydrologic cycle is a summary of the circulation of...
![Page 1: Chapter 16: Running Water. Hydrologic cycle The hydrologic cycle is a summary of the circulation of Earth’s water supply Processes involved in the hydrologic.](https://reader034.fdocuments.us/reader034/viewer/2022051315/56649eb45503460f94bbbc31/html5/thumbnails/1.jpg)
Chapter 16:
Running Water
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Hydrologic cycle
The hydrologic cycle is a summary of the circulation of Earth’s water supplyProcesses involved in the hydrologic cycle
• Precipitation• Evaporation• Infiltration• Runoff• Transpiration
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The hydrologic cycle
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Sources of Earth’s water
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Running water
Begins as sheetflow• Infiltration capacity is controlled by
– Intensity and duration of rainfall– Prior wetted condition of the soil– Soil texture– Slope of the land– Nature of the vegetative cover
• Sheetflow develops into tiny channels called rills
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Running water
Streamflow• Two types of flow determined primarily
by velocity– Laminar flow– Turbulent flow
• Factors that determine velocity– Gradient, or slope– Channel characteristics including shape, size,
and roughness
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Running Water
Streamflow• Factors that determine velocity
– 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– Viewed from the head (headwaters or source)
to the mouth of a stream
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Running water
Changes from upstream to downstream• Profile
– Profile is a smooth curve
– Gradient decreases downstream
• Factors that increase downstream– Velocity
– Discharge
– Channel size
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Longitudinal profile of a stream
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Running water
Changes from upstream to downstream• Factors that decrease downstream
– Gradient
– Channel roughness
Base level and graded streams• Base level is the lowest point to which a
stream can erode
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Running water
Base level and graded streams• Two general types of base level
– Ultimate (sea level)
– Local or temporary
• Changing conditions causes readjustment of stream activities
– Raising base level causes deposition
– Lowering base level causes erosion
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Adjustment of base level to changing conditions
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Running water
Stream erosion• Lifting loosely consolidated particles by
– Abrasion
– Dissolution
• Stronger currents lift particles more effectively
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Active erosion by a stream
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Running water
Transport of sediment by streams• Transported material is called the
stream’s load• Types of load
– Dissolved load– Suspended load– Bed load
• Capacity – the maximum load a stream can transport
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Running water
Competence • Indicates the maximum particle size a
stream can transport• Determined by the stream’s velocity
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Running water
Deposition of sediment by a stream• Caused by a decrease in velocity
– Competence is reduced
– Sediment begins to drop out
• Stream sediments– Generally well sorted
– Stream sediments are known as alluvium
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Running waterDeposition of sediment by a stream
• Channel deposits– Bars
– Deltas
• Floodplain deposits– Natural levees – form parallel to the stream
channel by successive floods over many years
– Back swamps
– Yazoo tributaries
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Formation of natural levees by repeated flooding
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Running waterDeposition of sediment by a stream
• Alluvial fans– Develop where a high-gradient stream leaves
a narrow valley
– Slopes outward in a broad arc
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Running water
Deposition of sediment by a stream• Deltas
– Forms when a stream enters an ocean or lake
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The Nile and Mississippi Rivers exhibit different types of deltas
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Mississippi River Delta
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Running water
Stream valleys• The most common landforms on Earth’s
surface• Two general types of stream valleys
– Narrow valleys– V-shaped – Downcutting toward base level– Features often include rapids and
waterfalls
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Running water
Stream valleys• Two general types of stream valleys
– Wide valleys
– Stream is near base level
– Downward erosion is less dominant
– Stream energy is directed from side to side forming a floodplain
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Running water
Stream valleys• Features of wide valleys often include
– Floodplains
– Erosional floodplains
– Depositional floodplains
– Meanders
– Cut bank and point bar
– Cutoffs and oxbow lakes
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Erosion and deposition along a meandering stream
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Erosion and creation of the floodplain
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Running water
Incised meanders and stream terraces• Incised meanders
– Meanders in steep, narrow valleys
– Caused 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
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A meander loop on the Colorado River
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Incised river in western Colorado
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Running water
Drainage Patterns Drainage Basin - the land area that contributes water to a stream.
Drainage Divide - the topographic boundary that separates two drainage basins.
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Running water
Drainage networks• Pattern of the interconnected network of
streams in an area• Common drainage patterns
– Dendritic
– Radial
– Rectangular
– Trellis
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Drainage Patterns
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Running water
Floods and flood control• Floods are the most common and most
destructive geologic hazard• Causes of flooding
– Result from naturally occurring and human-induced factors
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Running water
Floods and flood control• Flood control
– Engineering efforts
– Artificial levees
– Flood-control Dams
– Channelization
– Nonstructural approach through sound floodplain management
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Hoover dam
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End of Chapter 10