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EARTH EROSION PROCESSES

EARTH EROSION PROCESSES. __________________________ SITES 2005 INTEGRATED DEVELOPMENT ENVIRONMENT for WATER RESOURCE SITE ANALYSIS. OBJECTIVE. Introduce erosion theory related to earthen auxiliary spillways. BASIC EROSION PROCESSES RELEVANT TO EARTHEN AUXILIARY SPILLWAYS.

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EARTH EROSION PROCESSES

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  1. EARTH EROSION PROCESSES __________________________ SITES 2005 INTEGRATED DEVELOPMENT ENVIRONMENT for WATER RESOURCE SITE ANALYSIS

  2. OBJECTIVE Introduce erosion theory related to earthen auxiliary spillways

  3. BASIC EROSION PROCESSES RELEVANT TO EARTHEN AUXILIARY SPILLWAYS • SURFACE DETACHMENT VEGETATED EARTH CHANNEL FLOW BARE EARTH CHANNEL FLOW IMPINGING JET FLOW • HEADCUT ADVANCE

  4. SURFACE DETACHMENT

  5. er tc te

  6. SURFACE DETACHMENT . r = kd (e - c)a . r = the rate of detachment kd = coefficient of detachment e = effective stress c = critical tractive stress a = exponent (~ 1)

  7. EFFECTIVE STRESS • VEGETATION • e= ds(1-Cf) (ns/n)2

  8. EFFECTIVE STRESS • BARE EARTH • e=ds

  9. EFFECTIVE STRESS • AT THE HEADCUT • e= dc 0.011(H/dc)0.582 dc H e

  10. APPLICATION OF DETACHMENT RATE EQUATION IN VEGETATION e=  ds(1-Cf) (ns/n)2 . r = kd (e - c)

  11. ef te

  12. DETACHMENT RATE EQUATION gd 5.66gw ( )3.10 kd = exp[ -0.121(c%)0.41 ] gw gd kd = detachment rate coefficient gd = dry unit weight gw = unit weight of water c%= clay percentage

  13. t

  14. MASS MOVEMENT

  15. HEADCUT MIGRATION dx/dt = C (A - Ao) dX/dt = rate of headcut migration, C = material-dependent advance rate coefficient, A = hydraulic attack, and Ao = material-dependent threshold.

  16. HEADCUT MIGRATION RATE dX/dt

  17. HYDRAULIC ATTACK A = (q q H

  18. MATERIAL-DEPENDENT PARAMETERS AO & C are a function of Kh = headcut erodibility index

  19. HEADCUT ERODIBILITY INDEX, Kh Kh= MS x Kb x Kd x JS MS= material strength number of the earth material, Kb= block or particle size, Kd= discontinuity or inter- particle bond shear strength number, and Js= relative ground structure number.

  20. Condition of the Joints • Rough or smooth • Open or closed • Gap size • material in joints Block size Kb Kd Orientation to the flow Js

  21. Kh = 0.01 DESCRIPTION: SM, very loose sand with little bonding SITE: Buck and Doe Run 33, Missouri COMMENT: Eroding material in spillway breach: deep deposit

  22. Kh = 0.17 DESCRIPTION: CL , stiff SITE: Rush Creek 12R, Oklahoma COMMENT: Eroding material in headcut face.

  23. Kh = 0.5 DESCRIPTION: Disintegrated shale SITE: West Fork Point Remove 5, Arkansas COMMENT: Eroding material in gully bank.

  24. Kh = 20 DESCRIPTION: Jointed sandstone SITE: West Fork Pint Remove 5, Arkansas COMMENT: Material remaining below surface erosion. Some minor detachment by flow.

  25. Kh = 35000 DESCRIPTION: Massive rock (ryolite) SITE: Painted Rock Dam, Arizona COMMENT: Spillway outlet, negligible erosion.

  26. [ _ 189 Kh1/2exp(-3.23/ln(101Kh)) ]1/3 Kh> 0.01 AO = 0 Kh< 0.01 AND - 0.79 ln(Kh) + 3.04 Kh< 18.2 C = 0.75 Kh > 18.2 _

  27. Kh for MULTIPLE MATERIALS { } hi ln( Kh )i Kh = exp hi h1 Kh1 htotal h2 Kh2 h3 Kh3

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