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Levees

Levees. Artificial levees prevent floods Usually made with fine-grained sediments that are easily eroded in floods Higher-quality levees mix coarse gravel or face with riprap to resist erosion. Levees. 1800. 12. Recurrence Intervals and Discharge.

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Levees

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  1. Levees • Artificial levees prevent floods • Usually made with fine-grained sediments that are easily eroded in floods • Higher-quality levees mix coarse gravel or face with riprap to resist erosion

  2. Levees

  3. 1800 12

  4. Recurrence Intervals and Discharge

  5. Floods are more intense when ground is saturated

  6. Floods are more intense in urban areas

  7. Floods occur in areas without storms

  8. Flash Flood

  9. Flash floods are common in deserts • Time is < 6 hours • Water is not absorbed • >50% fatalities occur in vehicles • Slot canyons are bad for hikers • Can occur via dam failure • Natural dams (ice, quake) • Constructed dams

  10. Levee Failure

  11. Liouzhou, China (1996)

  12. Summer ‘08 20 Levees failed on Mississippi River Mississippi flooding near Meyer, Illinois, 6/21/08

  13. Unintended Consequences of Levees • Levee reduces width of flood-flow part of river and raises water level during flooding • Levees act to: • Eliminate storage of floodplain • Constrict flow and raise upstream water levels • Increase flood levels upstream and downstream

  14. Case In Point Repeated Flooding in Spite of Levees: Mississippi River Basin Flood, 1993

  15. Case In Point

  16. Iowa 1993

  17. Iowa 1993

  18. Iowa 1993

  19. Summary • Drainage basins and divides • Meandering vs. Braided • Deltas and Alluvial fans • Discharge calculation • Natural/artificial levees • Flood recurrence intervals

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