© 2012 Pearson Education, Inc. Water. © 2012 Pearson Education, Inc. Hydrologic Cycle The...
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Transcript of © 2012 Pearson Education, Inc. Water. © 2012 Pearson Education, Inc. Hydrologic Cycle The...
© 2012 Pearson Education, Inc.
Hydrologic Cycle• The hydrologic cycle is a model that
describes the movement of water through the reservoirs of the Earth
• Processes involved in the hydrologic cycle
• Precipitation• Evaporation• Infiltration• Runoff• Transpiration
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Hydrologic CycleEvaporation: Water
changes from liquid to vapor
Transpiration: Water taken up by plants passes into the atmosphere
Condensation: Water changes from vapor to liquid
Precipitation: Water returns to the surface of the earth as rain or snow.
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Hydrologic Cycle
Surface Runoff: precipitation that drains over the land or in streams
Infiltration: Water works its way into the ground through small openings in the soil.
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Streamflow
• Surface Runoff begins as overland or sheet flow as precipitation moves downhill
• Sheet flow eventually becomes a stream - water that flows downslope along a clearly-defined natural pathway.
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Streamflow Characteristics• Stream gradient - steepness of the slope. The gradient is highest near the stream’s headwaters (source) and decreases as it moves downslope toward the ocean.
• Stream discharge - the amount of water passing any point during a unit of time (example: ft3/sec).
• Stream load – suspended and dissolved sediment carried by the stream.
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Types of Stream Channels - Straight
Straight Channel
– Usually occur only in short stretches
– Generally have a high gradient (near headwaters)
– Classic V-shaped valley (as opposed to glacial U-shaped valley)
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Types of Stream Channels- Braided
Braided Channel
– Low gradient
– Large, variable sediment load that varies seasonally (e.g. snowmelt, storm activity)
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Types of Stream Channels- Meandering
Meandering Channel
– Usually occur downstream, near the mouth
– Low gradient
– Cut bank erosion and point bar deposition
– May eventually form an oxbow lake
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Oxbow Lake– Form when the meanders get too close together.
– River cuts a new, direct channel between the meanders. Meandering Channel
– Oxbow lake will eventually become a swamp and dry up.
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Stream Deposits
Floodplain – Flat valley floor adjacent to the stream, which is inundated when the stream overflows its banks
Alluvium – unconsolidated sediment deposited by the stream
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Stream Deposits – Alluvial Fans• Rapid change from
high gradient to low gradient environment causes stream to slow down and drop its sediment load.
• Fan-shaped deposit as water escapes its channel.
• Often found in arid to semiarid environments with infrequent rainfall/flash flood conditions.
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Stream Deposits – Delta• Similar to an alluvial
fan, but found at the mouth of the stream
• Fan-shaped deposit as stream flows into ocean and slows down, dropping its sediment load.
• Distinctive fan-shape looks like the Greek letter delta: Δ
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Drainage Basins• Drainage Basin: The
total land area that contributes water to a stream. Also called a watershed, or catchment basin.
• The drainage pattern consists of the interconnected network of streams in an area
• A drainage basin of one stream is separated from the drainage basin of another by an imaginary line called a divide.
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Successive drainage basins: The Yellowstone, Missouri, and Mississippi
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Surface water resources
• Fresh water supply– Essential for
• Direct human consumption• Crop and livestock• Industry
– Scarcity of water resources
• Many populations around the world lack access to clean drinking water
• Cause of socio-political conflicts
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Water-related conflicts in California• Colorado River
• Colorado River Compact among 7 states• Dispute between Imperial County and San Diego.
• Effect of Los Angeles Aqueduct on Mono Lake, Owens Lake, Owens River Gorge
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Groundwater - Subsurface water contained in pore spaces in sediment and rock
• Zone of aeration (vadose zone): pore space mainly filled with air
• Saturated zone (phreatic zone): pore space filled with water
• Water Table: Top surface of the saturated zone
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Groundwater• Groundwater moves
through the interconnected pore spaces of rock and sediment from areas of higher pressure to areas of lower pressure
• Rock porosity– Relative amount of space in underground rock
• Rock permeability– Ease of flow through rock
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Groundwater
• Water table tends to mimic topography
• The water table comes up to the surface at streams, springs, and lakes
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Discharge and Recharge
• Water percolation - Process of water seepage through rocks and sediment
• Recharge - Replenishment of groundwater• Discharge – process of water moving from the
subsurface to the surface.
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Aquifers and Aquicludes
• Aquifer– Saturated rock or sediment that is porous and permeable, so able to be accessed by well.
• Aquiclude– Layer of impermeable rock or sediment from which water cannot be drawn
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Types of Aquifers• Unconfined aquifer
– Water table not protected from surface recharge
– Vulnerable to surface and near surface contamination
– Well water rises to water table and must be pumped to surface
• Confined aquifer– Protected from surface by aquiclude,
– Recharge area is often distant
– Water under pressure and rises above water table in well