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Lecture 12

GLY-1103 Lecture Notes - Lecture 12: Aggradation, Thalweg, ProgradationPremium

2 pages52 viewsSpring 2017

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Brian Zimmer

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Streams and Flooding
Rivers only hold 0.0002% of all water
Drainage Basin (watershed)- the source region from which a stream draws its water
-Divide- ridge or crest that separates drainage basins from one another
-Runoff- precipitation that moves across the ground to enter streams
-Infiltration/Percolation- absorption and movement of precipitation or surface water into ground water
-Headwaters- where streams begin
-Base Level- endpoint of water or stream
Discharge- volume of water moving past a point in a stream in 1 second-- Q=WDV
Q= discharge W=width D=depth V=velocity
The fastest part of the stream is called the Thalweg
There is more friction in wider, shallower streams
Gradient= rise/run Percent Slope= rise/run x 100
The gradient is typically the steepest near the headwaters and the shallowest towards base level
Energy changes from source to base level
Affects sorting/ affects rate of downcutting or aggradation
Traction Load (Bed Load)- heavy debris rolled, pushed, or dragged across the stream floor
Suspended Load- material suspended by turbulence of the stream
Dissolved Load- material completely dissolved into the water
Shape of stream is also related to the type of material being cut into
Bedrock= steep sides
Soft Sediments= V-shaped
When river/stream velocity drops to zero, all remaining drops out and it forms a delta
Progradation- the river deposits sediments faster than the sea is able to remove them, so the delta
grows outward into the sea
Aggradation- the river deposits build up via overbank flooding accumulation of biotic remains etc., it
grows upward
Transgression- the retreat of the delta, usually by the loss of sediment caused by continued wave attack
or the reduction of nourishment soils
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