Infiltration and Soil Water

infiltration

passage of water through the soil surface
into the soil column

Why is infiltration dificult to measure

lots of heterogeneity in our soils

how to measure infiltration

pour water and wait for it to go into the ground

porosity

• function of grain size( clay pores are smaller so it is harder to infiltrate)

• influenced by compaction

• the amount of space

How ground water moves

• through tension and gravitational forces

water is held in pores due to

tension(suction, matric, capillary forces)

Capillary Rise

the phenomenon where a liquid, like water, flows upward in a narrow tube against gravity

capillary rise is caused by

– Attraction of water to the solid (adhesion)
– Surface tension of the water, which results from
cohesion of water molecules to one another
– Allows for upward migration

When its dry/ water is being drained what happens to the pores

large pores empty first

when it is wet what happens to the pores

small pores fill first

the more negative the pressure means

more tightly held the pores are/ the water is less moveable

Fully saturated water

• gravitational water

• no oxygen(anoxic/ anaerobic soils)

capillary water

lots of water and still oxygen

• good for plants

wilting point

• water is not accessible and plants die

Specific Yield

• Volume of water that drains from a saturated rock
  due to gravity

• Larger-grained sediments have greater specific yield

why can’t all water drain

adhesion and cohesion

when clay is at field capacity

• more water in it as appose to sand

why is clay functionally more drier

• water is held more tighter

spoil texture relationship to saturateion, field capacity, wilting point

Specific Retention

Ratio of the volume of water a rock retains against
gravity to the total volume of the rock

• Retention increases with decreasing grain size
– Clay will retain more water than sand

the smaller the grain =

more retention and less yield

permeability

• The ability of a soil to transmit water

• connectivity of soil pores

• influences infiltration

Homogeneity vs Heterogeneity

• uniformity vs a lack of uniformity.

• Amount of spatial variability

• influence infiltration

Influences on Infiltration

• Compaction
  • Soil structure
  • Organic material
  • Soil fauna
  • Water repellency
  • Land use
  • Antecedent soil moisture
  • Surface crusting/sealing
  • Frozen soil
  • Vegetation and residue
  • Surface detention
  • Time

How will porosity be impacted by the introduction of
various particle sizes?

– Porosity will be lowered
– Small particles will fill voids between large particles

How does the shape of particles influence porosity

– Spherical and other regular shapes can pack more tightly
• Lower effective porosity
– Irregular shapes cannot pack closely

Orientation of particles influence on porosity

– Orientation concerns non-spherical particles
• Rods, plates, books, etc.
•. Random orientation increases porosity