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Unsaturated zone / Soil MoistureOnverzadigde zone / bodemvocht

This lecture

• Discharge from unpaved land. The process of rainfall , infiltration and recharge of ground water

• Storage of water in soil? (Unsaturated zone)

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Example Hydrological cycleevapotranspiration

Transpiration275 mm

Evaporation75 mm

350 mm

Atmosphere

Precipitation800 mm

Ground level

Surfacerunoff25 mm 250 mm

425 mm

Sea

700 mm

275 mm

Open surface water system

Soil Moisture orUnsaturated zone

crops

Capillary rise50 mm

Absorption by roots

Water table orGroundwater level

Percolation orrecharge475 mm

Precipitation

Surface level

Unsaturated zone orSoil Moisture

Saturated zone1

Hydrological cycle (surface)

• Precipitation• Interception (leaves), delay and evaporation• Infiltration to soil (mm/day)• If net precipitation > infiltration

Storage in depression (Indication 10 mm)Surface runoff is possible

• No paved area

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Infiltration

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Grondsoort Soil

Indication Infiltration capacity (m/day)

matig grof zand moderate coarse sand 3

fijn zand met enige humus fine sand with some humus 0.3

Fijn zandige leem fine sandy loam 0.2

lichte zavel silt 0.3

matig zware klei clay 0.02

zandig veen sandy peat 0.1

veen peat 0.06

Dutch (Delta) situation

• Low intensity precipitation (100 mm 24 hour, = 4 mm / hour)

• High infiltration capacity• Land is horizontal and flat

• So little surface runoff

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Hydrological cycle (moisture) (bodemvocht) unsaturated zone

• Infiltration from surface• Percolation / Recharge ground water• Transpiration (roots)• Storage in pores• Forces on moisture (bodemvocht)

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Forces on Moisture• adsorption, osmotic and capillary forces.• Adsorption= H2O bond to negative soil parts • Osmotic=Cation’s ( pos zoutdeeltjes) cause a high

concentration of molucules at the soil part. This attracks H20 molucules.

• Adsorption and Osmotic bond water not available for plants

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Capillary action

• Cohesion ; intermolecular attraction between like molecules.

• Adhesion; attraction between unlike molecules

• Capillary action; Adhesion > Cohesion

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Capillary action

• Smaller pores have a stronger capillary force as bigger pores

• Equilibrium with gravitation3

Remarks?

• In the unsaturated zone there are forces which can slow down percolation(small pores are filled first)

• How many pores in the unsaturated zone are filled with water. How much is left for storage of water.

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Moisture curve

Wilting point

Water not available for plants

Volume water

pressure

sand

peatclayclay / sand mixturelight clay / sand mixture

Field capacity

Water available for plants

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(Verwelkingspunt)

pF cm

101,0 10

101,5 32

101,7 50

102,0 100

102,3 200

102,7 501

103,0 1000

103,4 2512

104,2 15849

Staring series Volume waterPressure (cm)

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pF cm101,0 10101,5 32101,7 50102,0 100102,3 200102,7 501103,0 1000103,4 2512104,2 15849

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Staring series, soil Nr. Bodemhorizonten Soils (translation is just an indication)

1 uiterst humusarm, matig fijn, leemarm zand little humus, little loam, moderately fine sand2 zeer humusarm, matig fijn, leemarm zand much humus, little loam, moderately fine sand3 matig humusarm, matig fijn, leemarm zand moderate humus, little loam, moderately fine sand4 matig humeus, matig fijn, leemarm zand moderate humus, little loam, moderately fine sand5 zeer humeus, matig fijn, leemarm zand much humus, little loam, moderately fine sand6 humusrijk, matig fijn, leemarm zand much humus, little loam, moderately fine sand7 zandig veen sandy peat8 veen peat

9uiterst humusarm, matig fijn tot zeer fijn, zwak lemig zand little humus, little loam, fine sand

10 uiterst humusarm, zeer fijn, sterk lemig zand little humus, much loam, fine sand11 uiterst humusarm, zeer fijn, zeer sterk lemig zand little humus, much loam, fine sand12 uiterst humusarme, zandige leem little humus, sandy loam13 uiterst humusarm, uiterst fijn, leemarm zand little humus, little loam, fine sand14 uiterst humusarm, matig grof, leemarm zand little humus, little loam, coarse sand15 zeer humusarme, lichte zavel Silt16 zeer humusarme, lichte zavel Silt17 zeer humusarme, lichte zavel Silt18 zeer humusarme, zware zavel Heavy silt loam19 zeer humusarme, lichte klei Silty clay loam20 zeer humusarme, zware klei Clay

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How to use the Staring series

• Relation between pressure and moisture content• Gives the potential storage in the unsaturated zone• Storage coefficient (bergingscoefficient)

= Volume available storage (m3) / Volume soil (m3)• Example storage coefficient = 0.02

Each m3 soil can store max 0.02 m3 of water5