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Infiltration

Infiltration. Infiltration definitions. Infiltration rate : the volume of water flowing into the soil profile per unit of surface area per unit time Infiltrability : the infiltration rate resulting when water at atmospheric pressure is made freely available at the soil surface

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Infiltration

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  1. Infiltration

  2. Infiltration definitions • Infiltration rate: the volume of water flowing into the soil profile per unit of surface area per unit time • Infiltrability: the infiltration rate resulting when water at atmospheric pressure is made freely available at the soil surface • Supply controlled: when the rate of water delivery to the surface is less than the infiltrability • Soil controlled: when the rate of water delivery to the surface is greater than the infiltrability

  3. Ponded infiltration

  4. (deep sandy loam)

  5. Green-Ampt model (1911) • a simplistic but elegant approximation of the ponded infiltration process • works best when: • wetting front is sharp • soil is coarse-textured • soil is initially dry • soil texture is homogeneous in the wetted region • air-entrapment and crusting are not significant

  6. Set the ponded infiltration rate equal to the rainfall intensity. Calculate the cumulative ponded infiltration for that rate. Assume that “the maximum possible infiltration rate at time t (t > 0) is determined uniquely by the value of the cumulative infiltration in the interval up to time t.” (Mls, 1980) Calculate time required for rainfall to supply the calculated cumulative infiltration. Kutílek, M. 1980. Constant-rainfall infiltration. Journal of Hydrology 45:289-303.

  7. Green-Ampt-Kutílek • To estimate time of ponding (tp) for rainfall at a constant rate (r) • Let H0 = 0, solve for Lf

  8. Example calculation • Rainfall at 1.5 cm h-1 • Silt loam soil • K = 0.65 cm h-1; • e = 0.49 m3 m-3 • i = 0.15 m3 m-3 • Hf = -17 cm of water • Estimate the time to ponding

  9. Preferential flow • water flow through distinct pathways that constitute only a fraction of the soil's total volume • promoted by • fine over coarse layering • hydrophobicity • air entrapment • clay or sand lenses • macropores formed by: • animals, roots, shrink-swell cracks, etc…

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