RB

GROUP 6 - INFILTRATION

INFILTRATION

  • Refers to the process where water from precipitation accumulates at the soil surface and either infiltrates into the soil or flows as runoff.

  • Infiltration enhances soil moisture, recharges aquifers, and supports streamflow during dry periods.

FACTORS AFFECTING INFILTRATION

Soil Characteristics

  • Type of Soil:

    • Silty Soil: High infiltration rates, low water retention.

    • Clayey Soil: Low infiltration rates, high water retention.

    • Sandy Soil: Moderate infiltration rates, high water retention.

    • Loamy Soil: Moderate infiltration rates, good water retention.

  • Degree of Saturation:

    • Saturated Soil: Low to zero infiltration.

    • Unsaturated Soil: High infiltration.

Soil Properties

  • Compressibility:

    • High Compressibility: Less water can infiltrate.

    • Low Compressibility: More water can infiltrate.

  • Porosity:

    • High Porosity: More water can infiltrate.

    • Low Porosity: Less water can infiltrate.

  • Permeability:

    • High Permeability: Quicker infiltration.

    • Low Permeability: Slower infiltration.

  • Capillarity:

    • Draws water upward through small pores.

    • High Capillarity: High water retention; Low Capillarity: Higher infiltration.

  • Cohesion:

    • High Cohesion: Low infiltration; Low Cohesion: High infiltration.

Surface Conditions

  • Crust Formation: Reduces infiltration by sealing the surface.

  • Land Use:

    • Urbanization reduces natural absorption, increasing runoff.

  • Soil Roughness:

    • Rough surfaces increase infiltration; smooth surfaces promote runoff.

  • Slope of the Land: Steeper slopes hinder infiltration.

Temperature and Biological Activity

  • Viscosity:

    • Warm Soil: Reduces viscosity, increases infiltration rates.

    • Cold Soil: Increases viscosity, decreases infiltration rates.

  • Biological Activity:

    • Warm Soil: Increase biological activity, increase infiltration rates.

    • Cold Soil: Reduced biological activity, reduced infiltration rates

  • Seasonal Variations:

    • Spring/Summer: Warmer soil increases infiltration.

    • Winter: Frozen soils reduce infiltration.

Vegetation Cover

  • Forests significantly enhance water infiltration.

  • Tundras display poor infiltration due to frozen ground.

  • Grasslands allow infiltration, while deserts vary based on soil type.

  • Ice sheets impede infiltration, contributing to runoff.

  • Desert, have varied infiltration depending on the soil type and vegetation density.

Other Influential Factors

  • Water Quality: Polluted water decreases permeability and clogs soil.

  • Rainfall Intensity: Heavy rainfall may surpass soil absorption capacity, leading to runoff.

  • Current Moisture Content: Drier soil allows for faster infiltration than already wet soil.

Infiltration Measurements

Infiltrometer Types

Infiltrometer

  • Is a device used to measure the rate of which water infiltrates into the soil.

  • Single Ring Infiltrometer: Measures infiltration rate by observing water depth variation in a cylindrical ring.

    • Common dimensions: 3 mm thick, 100 cm diameter, 50 cm height.

  • Double Ring Infiltrometer: Uses two concentric cylinders to estimate infiltration capacity with constant water levels.

    • Ring sizes: 3 mm thick, 30 cm inner diameter, 60 cm outer diameter, 50 cm height.

  • Rainfall Simulators: Replicate rainfall to measure surface runoff and calculate infiltration rates under controlled conditions.

  • Hydrograph Analysis: Estimates infiltration capacity by analyzing runoff hydrographs and rainfall records.

Infiltration Capacity and Rate

Infiltration Capacity

  • Defines the maximum absorption rate of soil over time, expressed in depth (mm/hr or inches/hr).

  • If precipitation rate (i) ≤ infiltration capacity (f): No surface runoff occurs.

  • If precipitation rate (i) > infiltration capacity (f): Surface runoff occurs.

    • Example: If i = 25 mm/hr and f = 15 mm/hr, runoff occurs at 10 mm/hr.

Infiltration Rate

  • Measures the speed (mm/hr or inches/hr) at which water enters the soil.

  • Initial infiltration is rapid, slowing down as pore spaces fill with water until a steady rate is reached.

REFERENCES

  • Various online educational resources and studies on infiltration, soil properties, and measurement methods.