InfiltrationReading AH Sec 4.3 to 4.4

InfiltrationGeneralProcess of water penetrating from ground into soilFactors affectingCondition of soil surface, vegetative cover, soil properties, hydraulic conductivity, antecedent soil moistureFour zonesSaturated, transmission, wetting, and wetting front

InfiltrationInfiltration rateRate at which water enters the soil at the surface (in/hr or cm/hr)Cumulative infiltrationAccumulated depth of water infiltrating during given time period

InfiltrometersSingle RingDouble Ringhttp://en.wikipedia.org/wiki/Infiltrometer

Infiltration MethodsHorton and Phillips Infiltration models developed as approximate solutions of an exact theory (Richards Equation)Green AmptInfiltration model developed from an approximate theory to an exact solution

Hortonian InfiltrationRecall Richards EquationAssume K and D are constants, not a function of q or zSolve for moisture diffusion at surface

f0 initial infiltration rate, fc is constant rate and k is decay constant

Hortonian Infiltration

Chart1

333

2.15582950581.84905840252.5339458274

1.60017068091.23441905642.1558295058

1.23441905640.90618213571.8490584025

0.99367015640.73089320121.6001706809

0.83520187090.63728334621.398244563

0.73089320120.58729271221.2344190564

0.66223404620.56059612691.1015051129

0.61704049150.5463393030.9936701564

0.58729271220.53872570640.9061821357

0.56771181460.53465980420.8352018709

0.55482306920.53248848340.7776145813

0.5463393030.53132892910.7308932012

0.54075502870.53070969030.6929874868

0.53707928870.53037899720.6622340462

0.53465980420.53020239650.6372833462

0.53306722560.53010808620.6170404915

0.53201894160.53005772140.600617178

0.53132892910.53003082510.5872927122

0.53087474180.53001646160.5764823853

0.53057578180.5300087910.5677118146

k1

k3

k2

k1 < k2 < k3

fc

f0

f1

f2

f3

Time

Infiltration rate, f

Sheet1

4.1826.2732.091

tf1f2f3

0333

0.12.15582950581.84905840252.5339458274

0.21.60017068091.23441905642.1558295058

0.31.23441905640.90618213571.8490584025

0.40.99367015640.73089320121.6001706809

0.50.83520187090.63728334621.398244563

0.60.73089320120.58729271221.2344190564

0.70.66223404620.56059612691.1015051129

0.80.61704049150.5463393030.9936701564

0.90.58729271220.53872570640.9061821357

10.56771181460.53465980420.8352018709

1.10.55482306920.53248848340.7776145813

1.20.5463393030.53132892910.7308932012

1.30.54075502870.53070969030.6929874868

1.40.53707928870.53037899720.6622340462

1.50.53465980420.53020239650.6372833462

1.60.53306722560.53010808620.6170404915

1.70.53201894160.53005772140.600617178

1.80.53132892910.53003082510.5872927122

1.90.53087474180.53001646160.5764823853

20.53057578180.5300087910.5677118146

Sheet2

Sheet3

MBD000A3D93.unknown

Philips EquationRecall Richards EquationAssume K and D are functions of q, not zSolutionTwo terms represent effects of Suction headGravity headS SorptivityFunction of soil suction potentialFound from experiment

Green Ampt InfiltrationWetted ZoneWetting FrontPonded WaterGround SurfaceDry Soil

Green Ampt Infiltration (Cont.)Apply finite difference to the derivative, between Ground surfaceWetting frontWetted ZoneWetting FrontGround SurfaceDry Soil

Green Ampt Infiltration (Cont.)Wetted ZoneWetting FrontGround SurfaceDry SoilIntegrateEvaluate the constant of integration

Green Ampt Infiltration (Cont.)Wetted ZoneWetting FrontGround SurfaceDry SoilNonlinear equation, requiring iterative solution.

Soil ParametersGreen-Ampt model requires Hydraulic conductivity, Porosity, Wetting Front Suction HeadEffective saturationEffective porosity

Soil Class

Porosity

Effective Porosity

Wetting Front Suction Head

Hydraulic Conductivity

n

e

(

K

(cm)

(cm/h)

Sand

0.437

0.417

4.95

11.78

Loam

0.463

0.434

9.89

0.34

Clay

0.475

0.385

31.63

0.03

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

Ponding TimeUp to the time of ponding, all rainfall has infiltrated (i = rainfall rate)

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