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Infiltration, Runoff and Stream flow

Explore the principles of infiltration in NREM 691 course presentation. Learn about measurement methods, factors affecting infiltration, impact of soil type, and flow through porous media. Discover equations like Green-Ampt, Horton, and Philip used to analyze infiltration phenomena.

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Infiltration, Runoff and Stream flow

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  1. Infiltration, Runoff and Stream flow Ali Fares, PhD Watershed Hydrology, NREM 691 UHM-CTAHR-NREM

  2. Presentation Outline • Infiltration • Definition & theory • Green-Ampt, Horton & Philip equations • Infiltration measurement • Infiltration as affected by: • Soil type

  3. Infiltration • Infiltration is the actual rate at which water is entering the soil at any given time(SCSA, 1976). • Infiltration capacity: Maximum rate (LT-1).

  4. Double ring infiltrometer Tension infiltrometer Guelph Permeameter Xiaodong, 2002 Measuring infiltration

  5. Effect of Rain Intensity Effect of Initial Water Content Soil Cover Effects Infiltration Characteristics • Infiltration is influence by: • Rain intensity, - Soil type -Disturbance. - Crust • Soil cover - etc.

  6. Taylor & Ashcroft, 1972 Soil Type Effects on Infiltration • Sand soils have the highest infiltration rates • Clay soils have the lowest infiltration rates. • High organic matter improves infiltration rates.

  7. H1 A Ksat L H2 Water Flow in Soil • The flux density, q, is the rate of water movement through a medium. • q is a function of ΔH and the hydraulic conductivity of the medium. • ΔH = H1 – H2 is the difference between total water potential inlet and outlet. • H = Pressure head + Gravitational head

  8. DERIVATION OF RICHARD’S EQUATION IN RECTANGULAR COORDINATES The general continuity equation is: Q = a q where Q is the flow rate, volume/time (L3/T) a is the cross-section area perpendicular to the flow, (L2) q is the flow velocity, length/time (L/T)

  9. FLOW THROUGH POROUS MEDIA In unsaturated soil the total potential can be estimated as the sum of the matric potential and the gravity potential: Since the gravity potential only acts in the vertical, or z-direction, the total potential, H, can be replaced by the matric potential, h, in all terms except the one involving z:

  10. z Dz x Dy Dx y FLOW THROUGH POROUS MEDIA

  11. From Continuity of mass Where Q is the volumetric water content and t is time.

  12. Applying the Darcy Law to each velocity term:

  13. Green-Ampt (1911): i = ic + b/I Where I is cumulative infiltration, ic and b are constants. There are several other equations: Horton (1940) Philip (1957) Infiltration Equations

  14. Horton’s Equation • Assumes K and D are constants (no dependence on q) • Richard’s equation reduces to the diffusion equation dq/dt = D [d2q/dz2] • Solve the equation for the rate of moisture diffusion at soil surface f(t) = fc + (f0 – fc) e–kt • k = Decay constant ~ T-1

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