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Landform Geography

Landform Geography. Landforms of the Fluvial System. Stream Gradation. Streams evolve to carry just the amount of sediment produced by their drainage basin. Meandering Stream. Stream carrying mostly suspended load usually has deep channel curving side-to-side. Braided Stream.

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Landform Geography

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  1. Landform Geography Landforms of the Fluvial System

  2. Stream Gradation • Streams evolve to carry just the amount of sediment produced by their drainage basin

  3. Meandering Stream • Stream carrying mostly suspended load usually has deep channel curving side-to-side

  4. Braided Stream • Streams with mostly bed load will have braided appearance – wide, shallow channel

  5. Graded Stream • A stream with just enough discharge to carry its average sediment load – at equilibrium • Aggradation – deposition on the bed of the channel due to added load or decreased discharge • Degradation – erosion of channel bed due to increased discharge or decreased load

  6. Evolution of a Graded Stream Base Level – lowest level at which a stream can erode its channel bed – can rise & fall with changes in sea or land level

  7. Niagara Falls • Upstream (Lake Erie) 571 ft elev • Downstream (Lake Ontario) 243 ft elev • Has retreated almost 7 miles in past 12,000 yrs

  8. Stream Meandering

  9. Oxbow Lake

  10. Floodplain Features

  11. Drainage Basin Changes

  12. Alluvial Fans • Created by alluvial aggradation in areas of high relief where bedload-dominated streams flow out of mts onto plain – stream sweeps side to side over time, making fan shape – most common in desert climates

  13. Deltas • River water slows as it enters ocean, depositing large amts of sediment in triangular pattern called delta – smaller particles farther out in delta

  14. Mississippi River

  15. Human Interaction with Streams • Urbanization • More impervious surfaces • After heavy rain, shorter lag time, higher peak flow – more serious flooding

  16. Dams and Reservoirs • Dam – engineered obstruction across a river to control its flow – usu. holds back lake or reservoir • Why dams? • 1. Hydroelectric energy • 2. Flood control • 3. Enhance river navigation • 4. Surface water supply Hoover Dam

  17. Chattahoochee and Buford Dam

  18. Negatives of Dams • Expense • Refugees from areas flooded by dam • Loss of ecosystems & scenery • No floods/No soil replenishment in floodplain • Stop spawning fish from going upstream

  19. Overland Flow • Perennial Streams – water runs all year • Ephemeral Streams – water runs only part of year • Sources of stream water: • Groundwater • Melting Ice • Surface Runoff

  20. Drainage Basins • Drainage Basin – area contributing groundwater and runoff to a stream • Drainage basins are divided from each other by topographic barriers called watersheds • Drainage Divide – elevated terrain forming rim around a drainage basin • Drainage basins vary tremendously in size • Basins are nested, smaller within larger

  21. Small, Nested Drainage Basins

  22. Common Drainage Pattern Types

  23. Major US Watersheds

  24. Drainage Density Total length of all streams Drainage Density = Area of drainage basin

  25. Stream Ordering • Represents stream size • Smallest streams in basin order 1 – order rises when 2 streams of same order come together at confluence

  26. Hydraulic Geometry • Geometric attributes of river channels • Variables: • w = channel width • d = channel depth • v = velocity of water • s = slope (steepness) also called gradient • Q = discharge (amt of water flowing) • Q = w x d x v (units m3/s or ft3/s)

  27. Hydraulic Variables

  28. Stream Hydrograph • Graph showing fluctuation in stream discharge over time • Lag between storm event and highest discharge • Base flow – flow rate sustained by groundwater influx

  29. Flooding • Flood Stage – stream discharge increases so that water spills out of channel onto adjoining ground • Return Period – time between events of a given magnitude, e.g. annual flood, 50-year flood, 100-year flood • Larger floods occur less frequently

  30. Mississippi River Floods - 1993 • At least 100-year flood, perhaps a 500-year flood • Heavy winter rains saturated ground • Stationary high pressure in Southeast in summer, blocking mid-latitude jet stream over Midwest • Cool, dry air collided with warm, moist air along jet stream, creating constant precipitation • Precipitation ran off into stream channels & rivers

  31. Mississippi River Floods - 1993

  32. 2009 Carrollton Floods

  33. Fluvial Processes and Landforms • Running water is most important geomorphic (landform shaping) process on Earth’s surface • All landforms due to either erosion or deposition • Erosional landforms occur when sediment, soil, or rock is stripped away from land • Depositional landforms occur where sediment accumulates after being dropped

  34. Depositional vs. Erosional Landforms

  35. Hillslopes • Most active zones of fluvial erosion due to high relief creating fast-moving, powerful water Rills Gully

  36. Ravine Canyon

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