Infiltration Reading AH Sec 4.3 to 4.4.

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Presentation transcript:

Infiltration Reading AH Sec 4.3 to 4.4

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 depth Wetting Zone Transmission Zone Transition Zone Saturation Zone Wetting Front q

Infiltration Infiltration rate Cumulative infiltration 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

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

Infiltration Methods Horton and Phillips Green – Ampt 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

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

Hortonian Infiltration

Philips Equation Recall Richard’s Equation Solution S – Sorptivity 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

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

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

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

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

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

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

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

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