18 Questions
What does the Horton Infiltration Capacity Curve represent?
The constant rate of infiltration reached after some time
In Horton's Infiltration Model, what happens when the rainfall rate exceeds the infiltration rate?
Infiltration rate decreases with time
How is infiltration modeled in the Green-Ampt Infiltration Equation?
As unsaturated flow
What factors influence the rate of infiltration in Horton's Infiltration Model?
Rainfall intensity, soil type, surface condition, and vegetal cover
What does the limiting curve in Horton's model define?
Maximum possible rates of infiltration vs. time
How does the filling of soil pores with water affect the infiltration capacity in Horton's model?
It reduces capillary suction
Which of the following is NOT one of the five principal assumptions associated with the topic discussed?
The soil under consideration is heterogeneous.
What does the uniform capillary suction just below the wetting front imply?
It is constant in time during the infiltration event.
In the Green-Ampt Infiltration Equation, what does the 'Wetting Front' represent?
Distinct boundary between saturated and unsaturated soil.
What does downward infiltration equal to in the Green-Ampt Method derivation?
Darcy Velocity
How does the moisture profile change at a later time according to the Green-Ampt Infiltration Equation?
Maintains a constant water content above and below the advancing wetting front.
What does Richard's Equation mainly describe in relation to soil characteristics?
Macropores and preferential migration pathways.
What parameter in the Green-Ampt formula depends on pore size and grain size properties?
Ks
In the Green-Ampt infiltration equation, what is the function of parameter Md?
Depends on effective porosity and initial saturation
What does the term 'Ponding Time' refer to in the context of the Green-Ampt method?
Time elapsed when ponding starts to happen
What does 'Ponding Depth' represent in the Green-Ampt method?
Depth of water infiltrated before ponding starts
Which parameter in the Green-Ampt formula represents the difference between atmospheric pressure and hydrostatic pressures?
𝝍
What function does parameter Ks serve in the Green-Ampt formula?
Determines pore size distribution
Study Notes
Infiltration Analysis
- Horton's Infiltration Capacity Curve shows how the infiltration rate decreases over time and eventually reaches a constant rate due to soil pores filling with water, reducing capillary suction.
Horton's Infiltration Model
- Developed by Horton in 1933, this model states that when rainfall rate (i) exceeds infiltration rate (f), water infiltrates surface soils at a decreasing rate over time.
- The model defines a limiting curve that represents the maximum possible infiltration rates versus time for a given soil.
- Factors affecting infiltration rate include rainfall intensity, soil type, surface condition, and vegetal cover.
Green-Ampt Infiltration Equation
- Developed by William Heber Green and Gustav Adolph Ampt, this model is based on unsaturated flow and utilizes Richard's Equation and Darcy's Law.
- Five principal assumptions of the Green-Ampt model are:
- Homogeneous and stable soil with no macropores or preferential migration pathways
- Unlimited supply of ponded water at the surface
- Distinct and precisely definable wetting front that advances at a constant rate with depth
- Uniform capillary suction below the wetting front
- Uniform saturation above the wetting front with constant volumetric water contents
- The model simplifies the infiltration process by assuming a distinct wetting front that advances with uniform capillary suction.
Green-Ampt Method Derivation
- Downward infiltration (-f) is equal to Darcy Velocity.
- Total Infiltration (F) is the cumulative infiltration over time.
Green-Ampt Formula Parameters
- Ks depends on pore size and grain size properties
- 𝝍 is the difference between atmospheric pressure and hydrostatic pressures
- Md is a function of effective porosity and initial saturation
Rainfall-Infiltration Scenarios
- Three possible scenarios: infiltration rate exceeds rainfall rate, rainfall rate exceeds infiltration rate, or both rates are equal.
Cumulative Infiltration and Ponding Time
- Cumulative infiltration increases with time according to the Green-Ampt formula.
- Ponding time is the amount of time that elapses before ponding starts to occur, and ponding depth is the depth of water infiltrated at this time.
Learn about Horton's Infiltration Model, which explains how water infiltrates surface soils with decreasing rates over time. Understand the concept of infiltration capacity curve and how it changes as soil pores fill up with water, reducing capillary suction.
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