SOIL WATERSOIL WATER

GES175, GES175, Science of SoilsScience of Soils

Water Movement- Surface water moves due to gravitational force

Does water always flow downward?

3.2

CapillarityCapillarity Water moves into capillary soil poresWater moves into capillary soil pores

- due to adhesive and cohesive forces- due to adhesive and cohesive forces

3.3

OH

H

OH

H

OH

H OH

H

OH

H

OH

H

OH

H

OH

H

K+

Cl-

OH

H

Osmotic Force

Water movement across semi-permeable membrane

3.4

Energy ConceptEnergy Concept

Water moves from Water moves from high to low free energyhigh to low free energy

wet soil wet soil dry soil dry soilHH22O movementO movement

HH22O freeO free H H22O freeO free energy isenergy is energy is energy is

higherhigher lower lower

- difference in free energy causes H- difference in free energy causes H22O to moveO to move

3.5

Large Pores Small Pores

Properties of WaterProperties of WaterHydrogen bondingHydrogen bonding

3.6

Capillary ForcesCapillary Forces

- smaller pores hold water with greater energy - smaller pores hold water with greater energy - nondirectional- nondirectional

h = 0.15/rh = 0.15/r

2T cos r d gh =

T = surface tension = wetting angler = radius of pored = density of waterg = gravity

3.7

Water Movement by Capillary Action3.8

3.9

UnitsUnits

cm Hcm H22OO barsbars kPakPa

300300 -0.3 -0.3 -30-30

1,0001,000 -1 -1 -100-100

10,00010,000 -10-10 -1000-1000

15,00015,000 -15-15 -1500-1500

see Table 5.1 in textsee Table 5.1 in text

3.10

1 atm = 760 mm Hg = 1020 cm H2O = 1 bar = 100 KPa

3.11

Sandy Soil

Clayey Soil

Water Content (%)

Suc

tion

(ba

rs)

0

-20

Water Retention Curves

Aggregated Soil

Water Content (%)

Suc

tion

(ba

rs)

0

-100

Compacted Soil

Water Retention Curves 3.12

Hysteresis

drying

wetting

Suction (bars)

2r

2R

drying

wetting

0 -100

0.5

3.13

Soil Water:Soil Water: Classification and AvailabilityClassification and Availability

physical biological0

-30

-15

-0.3

gravitational

capillary

vapor

values are only semiquantitativevalues are only semiquantitative

unavailable (drainage)

available

unavailable

(bars)

3.14

3.15

clayey

sandy

H2O

Concepts of Movement

sandy

clayey

H2O

clayey

sandy

H2O

3.16

Hpi

Hgi

Hinlet= Hpi + Hgi

Reference level

soil

Hpo

Hgo

Ho = Hpo + Hgo

H

H= Hinlet - Houtlet

= Hpi - Hpo

Saturated Flow- Horizontal Column

L

3.17

H1

L

inlet

Reference plainoutlet

Hi = H1 + L

Ho = 0 + 0

Saturated Flow- Vertical Column

H = H1 + L