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INFILTRATION

INFILTRATION. AE 520. Infiltration Lesson Objectives. Understand the factors affecting soil water infiltration Be able to estimate infiltration rate using the Horton Equation and the Green-Ampt Equation Understand the advantages of the various infiltration functions. INFILTRATE.

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INFILTRATION

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  1. INFILTRATION AE 520

  2. Infiltration Lesson Objectives • Understand the factors affecting soil water infiltration • Be able to estimate infiltration rate using the Horton Equation and the Green-Ampt Equation • Understand the advantages of the various infiltration functions.

  3. INFILTRATE To cause (as a liquid) to permeate something by penetrating its pores or interstices. Webster’s Ninth New Collegiate Dictionary

  4. INFILTRATION • The movement of water through the soil surface into the soil profile. • After Precipitation, it is the most important process controlling the water balance on a field. • Expressed as total depth or as a velocity called the infiltration rate

  5. Infiltration may be controlled by 3 types of factors • Supply Factors • Surface Factors • Profile Factors

  6. Infiltration Control Supply Factors • The water supply for infiltration may be: • Rainfall • Surface Pond Storage • Irrigation • Infiltration Rate will be the minimum of supply and Capacity

  7. Infiltration Control Surface Factors • Degree of Surface Crusting • Clay content of the surface • Effect of drop impact • Degree of Surface Porosity • Soil texture • Soil Structure • Vegetation Cover • Inwash of fine particles • Cracks and other macropores

  8. EFFECT OF PROTECTIVE COVER ON INFILTRATION

  9. Infiltration Control Profile Factors • Hydraulic Conductivity of the soil layers • Moisture Content of the soil layers near the surface. • Rate of internal drainage

  10. Runoff Infiltration Infiltration = Rainfall - Runoff Measurement of InfiltrationSprinkler Infiltrometer Rainfall

  11. Rate fc Time Infiltration with supply control Supply rate

  12. Measurement of InfiltrationRing Infiltrometer

  13. Infiltration with Soil Control Slope =fc DEPTH (F) TIME

  14. Infiltration with Soil Control fo INFILTRATION RATE (f) DEPTH / TIME fc TIME

  15. Field Surface Yp + Ym During Infiltration YT Static Z Soil Profile Water Table - 0 + POTENTIAL

  16. Kostiakov’s Equation F = CTn f = CnTn-1 log F n 1 C log T

  17. Horton’s Equation Log(f0 - fc ) 1 Log(f-fc) K t

  18. Darcy’s Equation

  19. SOIL MOISTURE CONTENT 0 ZONE OF SATURATION TRANSITION ZONE TRANSMISSION ZONE DEPTH FROM INFILTRATION SURFACE WETTING ZONE WETTING FRONT

  20. HOLTAN’S CONCEPT OF INFILTRATION F = Fmin+ S S = TOTAL POROSITY - WILTING POINT MOISTURE ABOVE THE CONFINING LAYER F = Fmin + S - ASM = Sr ACCUMULATED INFILTRATION DEPTH Fmin slope = fc TIME

  21. Holtan’s Equation log (f-fc) P 1 A 1 log ((S-F)/S)

  22. Green-Ampt Equation KDQDY f 1 K 1/F

  23. Green-Ampt Infiltration Equation 1 Soil Surface Yp = 0 K = Constant Yz = 0 Q = Qf= constant Wet Lf Ym = Yf Wetting Front 2 Yp = 0 Q = Qi = constant Yz = -Lf Dry Ym = Yi

  24. Green-Ampt Infiltration Equation

  25. Green-Ampt Infiltration Equation • Both Yi and Yf are negative and Yi < Yf . Therefore DY < 0 and the negative signs cancel.

  26. Green-Ampt Infiltration Equation • Total Depth of Infiltration = F • F = Lf(Qf - Qi) = LfDQ • Lf = F/DQ • assuming the velocity V = the infiltration rate f

  27. Green-Ampt Computations

  28. Infiltration Rate at the Beginning of a Time Increment

  29. Infiltration Rate at the Beginning of a Time Increment

  30. Average Infiltration Rate over a Time Period Rearranging:

  31. Upper Limit on the Infiltration During the Period

  32. Multiplying by F2 and Rearranging F1 will always be known or assumed. Therefore F2 is the only unknown, and the function is a quadratic.

  33. Quadratic Equation Solution for F2

  34. Quadratic Equation Solution for F2 • Only the +sign in the quadratic equation applies. • The actual value of F2 can not exceed F1 + Supply during the period. At the end of each time step, this limit must be checked, and if the GA equation gives a larger value, then the supply will be limiting.

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