Water Movement in Soil


When rainfall hits the earth’s surface,
one of two things can happen. Water can run off the land or often, with the help of
sound land management practices, water can move into the soil to be an
environmental positive rather than a negative. The soil itself has an influence on
whether water runs off or moves into the soil. Here’s a brief explanation of how and
why soils transmit water at different rates; and why you should check a soil survey
when you’re concerned about runoff, flooding, leaching, or other
environment hazards. Water movement in the soil is strongly
influenced by soil particle size (or texture), as well as structure and pore size. Soil texture is the relative amount
of sand, silt, and clay-sized soil particles. Sand particles are the largest, silt is
intermediate, and clay is the smallest. Water moves more quickly through the large
open macro pores found in sandy soils than the smaller pores of silt or the much smaller flat-shaped micro pores
in dense clay soils. Soil structure also impacts water movement. Water moves more quickly downward in
soils with granular structure than a soil with platy structure which forces
a longer, indirect path downward. Other structures include prismatic and sub-angular blocky. Water is nearly always moving in the
soil and it can be in any direction,
simultaneously. Gravity is the dominant force that moves
water downward. Restricted soil layers of compacted soil,
or bedrock, are among the reasons water moves laterally. Capillary action, the attraction of water into soil pores,
can move water in any direction. Gravity is the primary water moving
force in saturated soils, while capillary actions are the primary
forces in unsaturated soils. Capillary force is greatest in soils with
small pores. Water moves more slowly through these
soils. Well, that’s a brief explanation of what
a soil scientist calls saturated hydraulic conductivity. In simpler terms, the capacity of a soil
to transmit water. Since downward moving water carries
nutrients and can carry contaminants into underlying groundwater, soil percolation rates are important in choosing sites for septic fields, landfills, and other waste burials, as well as underground storage tanks and
other uses. The information is critical for planning
soil drainage, irrigation, and tillage systems, as well as other crop
management practices. Get the information you need on water
movement rates and other soil properties from a soil survey of your area on the web at www.soils.usda.gov.

14 thoughts on “Water Movement in Soil

  1. It is important to remember water is a resource that is constantly recycled and re-used. It is not like oil/petroleum. Water needs to be constantly cycled through the ecosystem in order to keep the earth healthy, grow crops, livestock, supply drinking water, etc.

  2. How can you talk about basic water movement in soil without mentioning surface litter, earth worms, root holes and the granular structure caused by soil microbes. You should re-title the video "Water Movement in Sub-Soil."

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