Which soil texture has the lowest hydraulic conductivity among common textures?

• A. Sand
• B. Silt
• C. Clay
• D. Gravel

Answer: (C)

Water movement through soil when it is saturated depends on pore size and how well those pores connect. Coarser textures have larger, more connected pores, so water can flow through them quite readily. Fine-textured soils have much smaller pores that are harder for water to navigate, and clays in particular form very tiny, winding pathways with high surface area and strong water adsorption. This combination creates many narrow, tortuous routes for water to travel, dramatically reducing the ease of flow. As a result, the saturated hydraulic conductivity is lowest in clay compared with sand, silt, or gravel.