1. Flowing Water: Sediment Transport and Landforms

2. Medium-term Plan 10/27Lecture 13. The Sediment Factory: Source to Sink 11/01Lecture 14. Flowing Water: Sediment Transport and Landforms 11/03Lecture 15. Depositional Systems(HW #4 assigned) 11/08Lecture 16. Dating the Sedimentary Record (Thompson) (HW #4 due) 11/10Lecture 17. Ice Age Cycles (Thompson) (HW #5?) 11/15Lecture 18: Waves and Coastal Morphodynamics 11/17Lecture 19: Shorelines(HW #6 assigned) 11/22The Anthropocene: Humans as Geomorphic Agents

3. Reynolds number (laminar vs. turbulent flow) u=flow velocity; l=characteristic length (flow depth);  =kinematic viscosity (dynamic viscosity/fluid density) (water ~ 1.5x10 -6 m 2 /s) Turbulence is promoted by high flow velocities and flow depths, and low viscosities (Re>2000); laminar flow occurs at Re<500 Air and water are nearly always turbulent

4. River Transport Transport of sediment depends upon

5. Settling Velocity and Cohesion Play bdld.mov

6. Rivers: Sediment transport Three modes: Dissolved load/wash load (ions in solution - pollution) Suspended load –Fine particles (sand, silt & clay) –Turbulent eddies pick up, carry upward if vel. > settling vel. Bedload –On/near bed; rolling, bouncing (‘saltating’), etc. Suspended and bedload increase rapidly with flow strength (nonlinear relationship)

7. Rivers: Two main kinds Alluvial rivers; bed consists of sediment (‘alluvium’ = river-associated sediment) –Downstream reaches Bedrock rivers; part of the bed is bare rock, where river cutting down –generally in upper reaches of rivers

9. Bedrock Rivers Erosion rate depends on slope Presence of sediment (‘tools’) increases erosion

10. Photo by Duncan Heron Alluvial Rivers

11. Landform: Floodplain

13. Braided stream

15. Braided streams are bedload dominated Nonlinear sediment transport laws result in dynamic feedbacks

16. Meandering stream; Point Bar and Cut Bank

17. Photo by Duncan Heron Point Bars and Cutbanks along river meanders Santee River, SC

18. Neuse River, NC Note point bars Photo by Duncan Heron

19. Oxbow lake formation Play meander.mov, sm1.mov

20. Incised Meanders

21. Natural Levee formation

22. Photo by Duncan Heron

23. Artificial Levees

24. Levee Failures

25. Crevasse Splay Deposits, Mississippi River

26. Natural River - 1948

27. 1964

28. Drainage Basins

29. Graded Stream Profile Flow increases downstream (tributaries) Velocity Increases Equilibrium slope reduces as flow increases

30. Graded Stream Profile Each stretch of alluvial river tends to have slope adjusted to transport sediment delivered to it Slope too low, sediment piles up at upstream end -> slope increases Slope too high, erosion (less in than out) at upstream end -> slope decreases Need steeper slope with Less flow Larger grains

31. Base Level Changes

32. Dam cuts off sediment flux

33. Shelf Transport System

34. Gravity Flows Debris flows have a high (>50%) proportion of sediment to water and can be both subaerial and subaqueous Can occur on land or underwater (Pratson.mov) Turbidity currents have a higher proportion of water, are always subaqueous, and move due to density contrasts

35. Pore Pressure Debris flows have a high (>50%) proportion of sediment to water and can be both subaerial and subaqueous

36. Pore Pressure Debris flows have a high (>50%) proportion of sediment to water and can be both subaerial and subaqueous Terrestrial flows: initial sediment packing affects type of flow Pratson.mov Pdfmod (weak debris flow) Pdfst6.mov (Strong debris flow)

37. Gravity Flows Debris flows have a high (>50%) proportion of sediment to water and can be both subaerial and subaqueous Can occur on land or underwater (Pratson.mov) Turbidity currents have a higher proportion of water, are always subaqueous, and move due to density contrasts The presence of a dilute suspension of sediment in the water of a turbidity current renders it slightly heavier than the ambient water. This results in downslope movement of both the sediment and entrained water (or vice versa). Sediment suspension can be from: catastrophic event (earthquake) flow-generated turbulence (autosuspension). wave stirring

38. Turbidity Currents turbwg.mov (turbidity current) Undf.mov (unconfined tc)

39. Turbidity Currents Turbidity currents also create levees, but can overtop them frequently

40. TURBIDITY CURRENTS – constructional and erosional

41. Passive (NJ/NY) Shelf

42. Monterey Submarine Canyon