1 / 11

Part 9

Part 9. LEVEES AND CREVASSES. Model levee design. The theory of levees proposed to confine the river’s mass in its main flow channel, encouraging scour during high flow. Natural crevasses beneath levees.

dominy
Download Presentation

Part 9

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Part 9 LEVEES AND CREVASSES

  2. Model levee design • The theory of levees proposed to confine the river’s mass in its main flow channel, encouraging scour during high flow.

  3. Natural crevasses beneath levees Crevasses are sand filled distributary channels that form at high flow, and lie beneath earthen levees like ticking time bombs, waiting to explode.

  4. Seepage crevasse exposed at the east levee of the IHNC breach in New Orleans after Hurricanes Katrina and Rita

  5. Permeability contrasts caused by clay filled oxbows create treacherous and contrasting foundation conditions beneath levees.

  6. The worst combination of foundation conditions is the ‘gore point’ formed between two infilled oxbows, as shown here.

  7. Clay filled oxbows consolidate under the load imposed by the earthen levees, causing these levees to settle and sink. Differential settlement is a major obstacle in maintaining levees.

  8. Raising Levees • The rising bed of the Mississippi River has necessitated the heightening of levees, beginning in the 1890s, as shown above. • Lower image shows dynamite charge being detonated on levee south of New Orleans in Plaquemines Parish during the Great 1927 flood.

  9. Levee Failures • Levees tend to fail during sustained high flow events because of underseepage problems, toe scour, and overtopping • This shows the 1999 Celotex levee failure in Louisiana, along the Mississippi River

  10. Most levees are compromised by underseepage. When a levee breaches, the sudden change in base level promotes rapid bed erosion, as shown here in the 1993 Missouri River flood.

More Related