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Infiltration

Infiltration. Reading AH Sec 4.3 to 4.4 . q. Saturation Zone. Transition Zone. Transmission Zone. Wetting Zone. Wetting Front. depth. Infiltration. General Process of water penetrating from ground into soil Factors affecting

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Infiltration

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  1. Infiltration Reading AH Sec 4.3 to 4.4

  2. q Saturation Zone Transition Zone Transmission Zone Wetting Zone Wetting Front depth Infiltration • General • Process of water penetrating from ground into soil • Factors affecting • Condition of soil surface, vegetative cover, soil properties, hydraulic conductivity, antecedent soil moisture • Four zones • Saturated, transmission, wetting, and wetting front

  3. Infiltration • Infiltration rate • Rate at which water enters the soil at the surface (in/hr or cm/hr) • Cumulative infiltration • Accumulated depth of water infiltrating during given time period

  4. Infiltrometers Single Ring Double Ring http://en.wikipedia.org/wiki/Infiltrometer

  5. Infiltration Methods • Horton and Phillips • Infiltration models developed as approximate solutions of an exact theory (Richard’s Equation) • Green – Ampt • Infiltration model developed from an approximate theory to an exact solution

  6. Hortonian Infiltration • Recall Richard’s Equation • Assume K and D are constants, not a function of q or z • Solve for moisture diffusion at surface f0 initial infiltration rate, fc is constant rate and k is decay constant

  7. Hortonian Infiltration

  8. Philips Equation • Recall Richard’s Equation • Assume K and D are functions of q, not z • Solution • Two terms represent effects of • Suction head • Gravity head • S – Sorptivity • Function of soil suction potential • Found from experiment

  9. Green – Ampt Infiltration Ponded Water Ground Surface Wetted Zone Wetting Front Dry Soil

  10. Green – Ampt Infiltration (Cont.) Ground Surface Wetted Zone • Apply finite difference to the derivative, between • Ground surface • Wetting front Wetting Front Dry Soil

  11. Green – Ampt Infiltration (Cont.) Ground Surface Wetted Zone Wetting Front Dry Soil Evaluate the constant of integration Integrate

  12. Green – Ampt Infiltration (Cont.) Ground Surface Wetted Zone Wetting Front Dry Soil Nonlinear equation, requiring iterative solution.

  13. Soil Parameters • Green-Ampt model requires • Hydraulic conductivity, Porosity, Wetting Front Suction Head Effective saturation Effective porosity

  14. Ponding time • Elapsed time between the time rainfall begins and the time water begins to pond on the soil surface (tp)

  15. Potential Infiltration Infiltration rate, f Rainfall Actual Infiltration Time Accumulated Rainfall Infiltration Cumulative Infiltration, F Time Ponding Time • Up to the time of ponding, all rainfall has infiltrated (i = rainfall rate)

  16. Example • Silty-Loam soil, 30% effective saturation, rainfall 5 cm/hr intensity

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