Soil Infiltration and Measurement

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Questions and Answers

Which stage is NOT part of the infiltration process?

  • Movement within the soil profile
  • Soil profile storage
  • Surface entry
  • Water evaporation (correct)

What is one of the key soil properties that affects infiltration?

  • Color of the soil
  • pH level
  • Porosity (correct)
  • Temperature

How do montmorillonitic clay soils affect infiltration after wetting?

  • They increase permeability.
  • They cause soil erosion.
  • They swell and reduce permeability. (correct)
  • They maintain high infiltration rates.

Which method is seldom used due to practical difficulties in measuring initial infiltration rates?

<p>Basin Method (C)</p> Signup and view all the answers

Which statement regarding vegetation's role in infiltration is correct?

<p>It enhances soil structure through organic matter production. (B)</p> Signup and view all the answers

What physical property of water influences its infiltration into soil?

<p>Viscosity (B)</p> Signup and view all the answers

Which soil type is characterized by high infiltration rates?

<p>Lateritic soils (C)</p> Signup and view all the answers

Which of the following factors is least likely to affect infiltration?

<p>Soil color (C)</p> Signup and view all the answers

What is the main advantage of using hydrograph analyses in infiltration studies?

<p>It provides infiltration data representative of the entire catchment. (D)</p> Signup and view all the answers

Which of the following correctly describes the Lewis-Kostiakov equation?

<p>It suggests that infiltration decreases to zero as time approaches infinity if there is an impermeable layer. (D)</p> Signup and view all the answers

What was Horton’s contribution to the understanding of infiltration rates?

<p>He established that continuous infiltration leads to decreased rates due to several physical processes. (C)</p> Signup and view all the answers

In the Gardner and Windsoe Equation, what do the constants C1 and C2 represent?

<p>Constants or parameters related to cumulative infiltration. (B)</p> Signup and view all the answers

What does the Philip equation primarily analyze?

<p>Vertical infiltration in porous media. (C)</p> Signup and view all the answers

Which phenomenon does the term 'exhaustion phenomenon' refer to in Horton’s analysis?

<p>The gradual decrease of infiltration due to various factors. (C)</p> Signup and view all the answers

Which condition allows the Lewis-Kostiakov equation to apply effectively?

<p>Soil must be underlain by an impermeable layer. (D)</p> Signup and view all the answers

What does the cumulative infiltration rate (i) indicate in the context of infiltration equations?

<p>The total amount of water that has infiltrated over time. (A)</p> Signup and view all the answers

Flashcards

Infiltration

The process of water entering the soil surface.

Initial Infiltration Rate

The high rate of infiltration at the beginning of water entry.

Soil Porosity

The amount of empty space within the soil.

Soil Structure

The arrangement of soil particles.

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Antecedent Soil Moisture

Water already present in the soil before new water enters.

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Infiltrometer

A tool used to measure infiltration rate.

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Basin Method

A way to measure infiltration by measuring the drop in ponded water.

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Watershed Hydrograph

Analyzing how much water runs off vs. infiltrates during rainfall.

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What is the main advantage of the procedure to subtract surface runoff rates?

The procedure provides infiltration data that is representative of the entire catchment.

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What type of equation is used to represent infiltration?

An infiltration equation describes the relationship between infiltration and time.

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Gardner and Windsoe Equation

This equation expresses cumulative infiltration as a function of time, using constants C1, C2, and β.

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Lewis-Kostiakov Equation

This equation relates cumulative infiltration (i) to time (t) using constants c and α, with α between 0 and 1.

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What does Lewis-Kostiakov equation imply about infiltration at t → ∞?

The equation implies that the infiltration rate will approach zero as time approaches infinity.

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Horton Equation

This equation describes infiltration rate as a decaying function of time, considering factors like soil storage potential and inwashing.

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Philip Equation

This equation describes vertical infiltration as a series that can be truncated after the first two terms without significant loss of accuracy.

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What does Philip Equation represent?

The equation represents cumulative infiltration as a function of the square root of time and a constant.

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Study Notes

Infiltration

  • Infiltration is the passage of water into the soil surface.
  • Initially, infiltration rates are high, but they decrease over time.
  • Factors affecting infiltration include:
    • Fluid properties (viscosity, turbidity, water depth)
    • Soil properties (porosity, structure, surface stability, moisture holding capacity, antecedent soil moisture, mineralogy)
    • Vegetation and soil cultural practices (vegetal cover protects soil, tillage increases surface entry rate)

Measurement of Infiltration

  • Methods for measuring infiltration include:

    • Infiltrometers: Commonly involve a double ring design; water is added to the inner ring and infiltration is measured over time. Specific details like the size (60 cm ring, 30 cm ring, 12 cm above soil surface, 15 cm into soil) of the rings are noted.

    • Basin Method: Involves flooding a large area and measuring the rate of drop in ponded water depth over time. It is not a practical method.

    • Watershed Hydrograph Method: Involves analyzing runoff and rainfall from watersheds to characterize infiltration. The procedure subtracts runoff rates from total streamflow and adjusts for evapotranspiration and detention.

Infiltration Equations

  • Gardner and Windsoe Equation (1921): i = C₁t + C2 (1-e-kt) (where i is cumulative infiltration, t is time, and C1, C2, and k are constants)

  • Lewis-Kostiakov Equation (1932, 1937): i = cta; f = act(a-1)(where i is cumulative infiltration, t is time, and c and a are constants)

    • The equation applies best when the soil has an impermeable layer beneath it.

  • Horton Equation (1940): i = fc + (f0 - fc)(1 - e-kt) (where i is infiltration rate, fc is the final constant rate of infiltration, f0 is the initial maximum rate of infiltration, t is time and k is a decay constant)

    • This equation considers that continuous infiltration and wetting affect the rate of infiltration.

  • Philip Equation (1957): i = St1/2 + At (where i is infiltration rate, S and A are constants, and t is time)

    • This is a partial differential equation describing water movement as a rapidly converging series, often truncated fairly readily.

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