11
Freshwater
Environments
+ Water
Resources
© Cengage Learning 2015
11.1 The Water Cycle
• Hydrologic cycle – movement of water
through the four spheres
– Moves energy
• Fate of precipitation
– Runoff
– Groundwater
– Transpiration
– Water cycles moves energy
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© Cengage Learning 2015
© Cengage Learning 2015
11.2 Streams
• Flowing water in a channel
– River – large stream fed by tributaries
• Stream flow and velocity
– Gradient – steepness
– Discharge – volume of water flowing/unit time
– Channel characteristics
• Bank
• Bed
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Streams
• Stream erosion and transport
– Competence – largest particles
– Capacity – maximum quantity of sediment
– Dissolved load – ions
– Suspended load – portion that remains
suspended
• Function of size and velocity
– Bed load – rolls, skips or bounces along the
bottom
© Cengage Learning 2015
Streams
• Downcutting and base level
– Downward erosion
• Function of discharge, gradient, bed composition
– Base level – as far as the stream can erode
• Sea level is ultimate base level
• Bed composition, etc., can interfere
– Graded stream
• When a stream reaches a base level over the
course of its gradient
© Cengage Learning 2015
© Cengage Learning 2015
© Cengage Learning 2015
© Cengage Learning 2015
Streams
• Sinuosity of stream channels
– Lateral erosion – sidewards erosion
• Common in low-gradient streams
– Meander – loops caused by lateral erosion
– Point bar – depositional area, usually on “inside”
of meander loop
– Oxbow lake – meander that gets pinched off
– Braided stream – network of interconnected
channels
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© Cengage Learning 2015
© Cengage Learning 2015
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Streams
• Drainage basins and drainage divides
– Drainage basin
• An area of land that feeds into a river or stream
• Contiguous land that is all “downhill”
– Drainage divides
• Separate drainage basins
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© Cengage Learning 2015
Streams
• Stream erosion and mountains
– Streams continuously erode towards base
level along their length
– At the same time, tectonics tend to uplift land
– Interplay in a dynamic equilibrium
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11.3 Stream Deposition
• Alluvial fan – deposition into dry terrain
• Delta – deposition into aqueous
environment
– Distributaries – fan of water channels in a
delta
– Submarine delta – deposition below the
water’s surface
• Avulsion
– Stream channel is abandoned
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© Cengage Learning 2015
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© Cengage Learning 2015
Ganges-Brahmaputra River Delta
From Landsat 7 WRS Path 137 Row 44, center: 23.12, 90.37. Image taken 2/28/2000
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11.4 Floods
• Flood – more water than a channel can
hold
– Hazardous natural system
– Flood dynamics are altered by human action
• Flood plain – low-lying land adjacent to a
stream channel
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Floods
• Flood control
– Artificial levees – constructed embankment
along stream channel
• Give adjacent populace a false sense of security
• Levees cause stream to deposit in the channel,
raising the base
– Artificial channels – dredging to straighten a
river to increase gradient and velocity
• Scours more sediment
© Cengage Learning 2015
© Cengage Learning 2015
Los Angeles River: 2005 Flood and Now
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© Cengage Learning 2015
© Cengage Learning 2015
Fluvial Processes and Landscapes
at Different Stream Stages
Stage
Landscape
Processes
Youthful
Steep hillsides,
drainage divides predominant,
V-shaped valleys
Headward erosion,
stream downcutting –
vertical erosion
Mature
Rounded hills,
valley walls predominant,
graded streams,
broad floodplains
Lateral erosion,
streams adjust to
discharge/load
Floodplains, ox-bow lakes,
deltas and alluvial plains,
very low relief
Deposition,
sluggish stream flow,
poor drainage
Old age
© Cengage Learning 2015
11.5 Lakes
• Large, inland body of standing water
occupying a surface depression
– Kettle lake – lakes caused initially by blocks of
remnant glacial ice
– Oxbow lake
– Volcanic crater lake
– Fault lakes
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Lakes
• Nutrient balances
– Oligotrophic – poorly nourished
• Blue, clear water
• Low productivity, limited organisms
– Eutrophic – high nutrient supply
• Often littered / green water
• High productivity, dense vegetation/algae
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© Cengage Learning 2015
© Cengage Learning 2015
Lakes
• Temperature layering and turnover
– Thermocline – boundary between warm and
cold layers
– Turnover – autumn cools top layers, water
sinks and displaces warmer, deep water
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© Cengage Learning 2015
11.6 Wetlands
• Areas that are:
– Wet part of the time
– Anaerobic soils
– Plants adapted to periodic flooding
• Types of wetlands
– Swamps
– Bogs
– Marshes
© Cengage Learning 2015
© Cengage Learning 2015
11.7 Ground Water
• Water that exists in sediment pores, or
cracks and fractures in rock
• Porosity – the proportional volume of
empty space
• Permeability – the ability for Earth
materials to transmit fluids (water)
© Cengage Learning 2015
Groundwater
• Water table and aquifers
– Zone of saturation – all pores filled with water
– Water table – top of the saturated zone
– Zone of aeration – pores above the water
table
– Recharge – water seeping into the saturated
zone
– Aquifer – body of porous Earth material that
can provide useful amounts of water
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© Cengage Learning 2015
Groundwater
• Movement – “shape” of ground water
mimics the surface, highs and lows
– Generally moves from high to low
• Spring – water table intersects land
surface
• Perched water table – impermeable layer
• Artesian aquifer – inclined and bounded by
impermeable layers
• Artesian well – pressurized well into an
artesian aquifer
© Cengage Learning 2015
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© Cengage Learning 2015
Groundwater
• Caverns, sinkholes and karst
– Cavern – cavity formed by water dissolving
soluble rock
– Sinkhole – roof of a cavern casing surface
collapse
– Karst topography – area underlain by soluble
rock that develops many sinkholes and
caverns
© Cengage Learning 2015
© Cengage Learning 2015
11.8 Hot Springs, Geysers, and Geothermal
Energy
• Hot spring – ground water heated by an
igneous heat source that is found at the
surface
• Geyser – a hot spring that explosively
releases pressure
• Geothermal energy – using Earth’s heat
for electricity or heating
© Cengage Learning 2015
© Cengage Learning 2015