161.%20Rivers - Rivers Lecture 16 Rivers are Lecture 16...

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Unformatted text preview: Rivers Lecture 16 Rivers are: Lecture 16: Rivers Page 1 of 26 Lecture 16: Rivers Rivers are: Rivers are: Lecture 16: Rivers Page 2 of 26 Lecture 16: Rivers Rivers are: Rivers are: Lecture 16: Rivers Page 3 of 26 Lecture 16: Rivers Rivers are: Rivers are: Lecture 16: Rivers Page 4 of 26 Lecture 16: Rivers Drainage Basin The entire catchment The area for a river system Steep gradient in Steep headwaters becoming very flat at the delta Stream patterns and Stream sediment load change with position in the basin Stream Patterns Stream Reflect the geology Reflect Dendritic: no Dendritic: geological control Trellis: dipping beds Trellis: control Angular: fracture/fault Angular: control Radial: Dome/Cone Radial: controls Lecture 16: Rivers Page 5 of 26 Lecture 16: Rivers Stream Morphology Mountain Stream Steep gradient Steep Bed load dominated Bed Bedrock floor Bedrock Minimum flood plain Minimum Clear water flow Clear Features of a Braided Stream Steep gradient Bed load dominated Coarse grained sediment Narrow flood plain Clear water flow Lecture 16: Rivers Page 6 of 26 Lecture 16: Rivers Braided Stream Rock Flour Lecture 16: Rivers Page 7 of 26 Lecture 16: Rivers Transition Channel Lecture 16: Rivers Page 8 of 26 Lecture 16: Rivers Features of a Meandering River Moderate gradient Moderate Combined sediment Combined load (bed + suspended load) Single channel Single Large floodplain Large Often a “misfit” Often system Meandering River Lecture 16: Rivers Page 9 of 26 Lecture 16: Rivers Meander Cut-Off Accelerated erosion Accelerated along the outside of a meander Coupled meanders Coupled eventually merge Meander is cut-off Meander and river geometry is abruptly altered Cut-Off at the Bend Lecture 16: Rivers Page 10 of 26 Lecture 16: Rivers Lecture 16: Rivers Page 11 of 26 Lecture 16: Rivers Lecture 16: Rivers Page 12 of 26 Lecture 16: Rivers Features of a Delta Plain Very low gradient Very Suspended load Suspended transport Highly meandering Highly channel Single channel Single Broad wetland Broad dominated floodplain Delta Plain River Lecture 16: Rivers Page 13 of 26 Lecture 16: Rivers Floodplain/Delta Plain Swamps Wetland forest or Wetland grassland ecology Environmentally Environmentally sensitive Very low gradient Very Dominantly clay and Dominantly organic sediments Critical role in Critical pollution control River-Ocean Interface River Formation of a river mouth bar, a constant threat Formation to marine traffic Mechanism that creates the summer season Mechanism “Dead Zone” in the Gulf of Mexico Lecture 16: Rivers Page 14 of 26 Lecture 16: Rivers Channel Hydrodynamics Helical flow attacks the Helical outside of a bend and transports sediment to the inside of the bend – forming a point bar Helical flow is balanced Helical in the straight portion of the channel Knick-Points, Waterfalls Lecture 16: Rivers Page 15 of 26 Lecture 16: Rivers Knick-Point Erosion Knick-Point Erosion Mechanics Natural: Unvented Knick-Point Vented Knick-Point Lecture 16: Rivers Page 16 of 26 Lecture 16: Rivers Erosion Controlled by Stratigraphy Lecture 16: Rivers Page 17 of 26 Lecture 16: Rivers Canyon at Canyon Lake Lecture 16: Rivers Page 18 of 26 Lecture 16: Rivers River Sediment Transport Cohesive soils have high cohesion = high energy to erode Non-cohesive soils have low cohesion = erosion related to boundary shear/sediment size Combine Cohesion + Size Yields Lecture 16: Rivers Page 19 of 26 Lecture 16: Rivers Sediment Transport Lecture 16: Rivers Page 20 of 26 Lecture 16: Rivers Impact of Land Use Changes Undeveloped land: Minimum runoff and Maximum infiltration results in reduced runoff Urban Development: Decreases infiltration, Decreases Lag Time which Increases Runoff leading to Urban Flooding Lecture 16: Rivers Page 21 of 26 Lecture 16: Rivers Rational Equation Estimates Runoff based upon land use Lecture 16: Rivers Page 22 of 26 Lecture 16: Rivers Impact of Urbanization Climate Data Lecture 16: Rivers Page 23 of 26 Lecture 16: Rivers Recurrence Interval Precipitation Data Lecture 16: Rivers Page 24 of 26 Lecture 16: Rivers Determine Runoff for Pond River Erosion Control Rock, Rip Rap, used to stabilize cut bank Used water tanks create a reinforced bank Lecture 16: Rivers Page 25 of 26 Lecture 16: Rivers Break Lecture 16: Rivers Page 26 of 26 Lecture 16: Rivers ...
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