and humid areas are fragile. . Soil gets eroded by wind and water. Productive land becomes degraded. Main culprits:. Overgrazing. Overplowing. . Human activity can stress . the ecosystem. . • Grazing. ID: 228645
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Transition zones between desertsand humid areas are fragileSlide4Slide5
Soil gets eroded by wind and water
Productive land becomes degraded
Human activity can stress the ecosystem
• Grazing• Cutting trees for charcoal• Some agricultureSlide8Slide9Slide10
Drainage BasinsDischargeSediment loadMeandering/Braided riversFloodplainsFlooding
+ 336 Runoff from land
+ 398 Precipitation over sea+ 434 Evaporation
+ 434 Evaporation– 398 Precipitation + 436 Excess to land via precipitation
+ 107 Precipitation– 371 Evaporation+ 436 Runoff to ocean
+ 107 Precipitation– 336 Runoff to ocean+ 471 Evaporation
Flux in and flux out over oceans is almost balanced.
Excess is moved toland and precipitates.
…or filters into soiland rock, where it moves as groundwater.
The precipitationruns off intolakes, streams,and oceans…Slide12
Rio Grande River basin includes:
Pecos (and all of its tributaries)
It doesn’t include the Gila, because it flows into Colorado
Continental Divide (in NM) separates:
Rio Grande drainage
Colorado River drainageSlide15
Rio Grande WatershedSlide17Slide18Slide19Slide20
Stream profile depends on locationSlide21
Q=VAQ is dischargeV is average velocity (m/s)A is cross-sectional area (m2)units of Q?
Sediment Load and Grain Size
Streams can be provided with particles of any size from mud to giant bouldersVolume and velocity of flow limit size and amount of sediment that stream can carrySlide25
Sediment Load and Grain SizeSlide26
Sediment Transport and FloodingSlide27
Meandering: low sediment content, gentle gradient, more vegetation
Braided: high sediment content, steep gradient, unstable channelsSlide28
Nenana River, Alaska
Green River, Utah
Size and shape of river meanders:Meander wavelength, width and arc lengthRatios are constant regardless of stream sizeSlide32
Erosion/deposition of meanders creates floodplainSlow water velocity forms natural levee Keeps small floods within channelSlide33Slide34Slide35Slide36Slide37Slide38
Low-velocity, low-sedimentstreams form meanders.
Meanders shift from side to
side in a snaking motion.
Sediments get deposited in
inside banks forming point
The bends grow closer and
the point bars bigger.
During a major flood, the
river cuts across the loop.
The current is faster at outside
banks, which are eroded.
The abandoned loop remains
as an oxbow lake.Slide39
Meanders in an Alaskan river
flow in channelSlide40
Multi-channel pathsOverloaded with sediment that is deposited in islandsPromoted by dry climate, glacier outwash, alluvial fansSlide42
Cook Inlet, AlaskaSlide43
Sandy braided River: Red River, Texas-OklahomaSlide44
Braided glacial outwash, Gulf of Alaska
Braided rivers are common near glaciersSlide45
Alluvial fans have braided streamsSlide46
Gravel delta at mouth of braided river, Cook Inlet, AlaskaSlide47
Delta reworked by wave action, Cook Inlet, Alaska