Tension infiltrometerDouble ring infiltrometer Guelph Permeameter Measuring infiltration
Infiltration Characteristics Infiltration is influence by: – Rain intensity,- Soil type -Disturbance. - Crust – Soil cover- etc.
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.
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 = H 1 – H 2 is the difference between total water potential inlet and outlet. H = Pressure head + Gravitational head L A H1H1 H2H2 K sat
DERIVATION OF RICHARD ’ S EQUATION IN RECTANGULAR COORDINATES The general continuity equation is: Q = a q where Q is the flow rate, volume/time (L 3 /T) a is the cross-section area perpendicular to the flow, (L 2 ) q is the flow velocity, length/time (L/T)
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: FLOW THROUGH POROUS MEDIA
Infiltration Equations Green-Ampt (1911): i = i c + b/I Where I is cumulative infiltration, i c and b are constants. There are several other equations: Horton (1940) Philip (1957)
Horton ’ s Equation – Assumes K and D are constants (no dependence on q) – Richard’s equation reduces to the diffusion equation dq/dt = D [d 2 q/dz 2 ] – Solve the equation for the rate of moisture diffusion at soil surface f(t) = f c + (f 0 – f c ) e –kt – k = Decay constant ~ T -1