Lecture on Water Movement in Soil

Overview

• Rainfall can either run off the land or infiltrate the soil.
• Land management practices influence whether water infiltration is positive for the environment.
• Soil characteristics determine water movement, affecting runoff, flooding, leaching, and other hazards.

Factors Influencing Water Movement in Soil

Soil Texture

• Definition: Relative amounts of sand, silt, and clay particles.
• Particle Sizes:
  • Sand: Largest
  • Silt: Intermediate
  • Clay: Smallest
• Water Movement:
  • Faster through sandy soils due to large macro pores.
  • Slower in silt and clay due to smaller pores.

Soil Structure

• Types:
  • Granular: Promotes quicker downward water movement.
  • Platy: Causes water to take longer, indirect paths.
  • Other structures: Prismatic and sub-angular blocking.

Forces and Directions of Water Movement

• Gravity: Dominant force moving water downward.
• Capillary Action: Water is attracted into soil pores, moving in any direction.
  • Most significant in unsaturated soils with small pores.

Saturated Hydraulic Conductivity

• Definition: Soil's capacity to transmit water.
• Importance:
  • Preventing nutrient and contaminant movement into groundwater.
  • Influences site selection for septic fields, landfills, and storage tanks.
  • Critical for planning drainage, irrigation, tillage, and crop management.

Practical Applications

• Use soil surveys to obtain data on water movement rates and soil properties.
• Resources available at:
  • Website: www.soil.gov
  • Additional Info: usdobuilds.usda.gov

These notes summarize the key concepts regarding how water interacts with soil, the factors affecting this interaction, and the practical implications for environmental and agricultural management.