Saturated Hydraulic Conductivity
- Soils with low porosity, few large pores and poor interconnectivity between pores have low values of K. Saturated hydraulic conductivities were highest in coarse-textured soils and declined in fine-textured soil, due to larger pores in the former.
- This was corroborated by examining air entry potential (matric potential at which largest capillary pores empties) more negative in fine textured soil which indicates small number of large capillary pores in fine textured soil than coarse textured soil. Thus, coarse textured soil has high K inspite of low porosity.
Unsaturated Water Flow in Soil
- Unsaturated water flow occurs in soils where pores are only partially filled with water, with the remaining space occupied by air. This zone, known as the vadose zone, lies between the soil surface and the water table.
- Unlike saturated conditions, water content here is below full capacity, resulting in negative pressure heads. The primary driving force is the matric potential, which represents the suction created by water adhesion to soil particles and capillary action in small pores. This negative pressure potential dominates over gravitational forces in finer soils.
- Hydraulic conductivity in unsaturated soils is significantly lower than in saturated conditions because water moves primarily through smaller pores or as thin films along the walls of larger pores. As larger pores drain first, the remaining pathways for water become more restricted, slowing movement. Flow in this zone is typically transient (unsteady), meaning the rate and volume of water movement vary over time.
- Understanding unsaturated flow is critical for multiple applications. It controls aquifer recharge rates, influencing how water percolates down to groundwater systems. It also plays a key role in contaminant transport, determining how pollutants disperse through soil. In agriculture, it affects water availability to plant roots and irrigation efficiency, making it essential for sustainable land and water management.