Hydrologic Soil Groups

Hydrologic Soil Groups, abbreviated as HSG, are a classification system used in hydrology and soil science to categorize soils based on their ability to infiltrate water.  These groups help in assessing how different soils affect the movement of water, which is crucial for various applications such as land use planning, stormwater management, and agricultural practices.  The United States Natural Resources Conservation Service (NRCS) developed the hydrologic soil group classification system, which is widely used in the United States.

Hydrologic Soil Groups are typically designated by the letters A, B, C, and D, with each letter representing a specific level of soil infiltration capacity

• Hydrologic Soil Group A (High Infiltration)  -
  
  • Soils in this group have high infiltration rates, allowing water to move through them rapidly.  These soils are typically well drained and have good water holding capacity.
  • Examples include sandy soils and loamy soils with good permeability.
• Hydrologic Soil Group B (Moderate Infiltration)  -
  
  • Soils in this group have moderate infiltration rates, meaning they can absorb water at a moderate pace but may become saturated over time.
  • Examples include soils with a moderate mix of sand, silt, and clay.
• Hydrologic Soil Group C (Slow Infiltration)  -
  
  • Soils in this group have slow infiltration rates, meaning they do not readily absorb water, and water often ponds on the surface or runs off before being absorbed.
  • Examples include clayey soils with poor permeability.
• Hydrologic Soil Group D (Very Slow Infiltration)  -
  
  • Soils in this group have very slow infiltration rates, making them almost impermeable to water.  Water tends to pond or run off quickly on these soils.
  • Examples include hardpans, rocky soils, and soils with high clay content.

These soil groups are essential for assessing runoff potential, determining suitable locations for construction, designing stormwater management systems, and understanding how different land uses can impact water infiltration and runoff.  By categorizing soils into hydrologic soil groups, land planners and engineers can make informed decisions about land development, erosion control, and water resource management.