ProdukHukum Pendidikan

(1)

L3 Vadose Zone Hydrology and

Groundwater Recharge

Tsutomu Yamanaka

TERC, Univ. of Tsukuba

The 20th IHP Training Course

“Groundwater as a key for adaptation to

changing climate and society”

Nov. 09, 2010 @ Nagoya University

(2)

Question

What are the key variables in ensuring

sustainable use of groundwater resources ?

(3)

Sustainability of groundwater use

What are the key variables in ensuring sustainable use of groundwater resources ?

Storage

volume

Renewal

rate

(4)

Aquifer systems in arid regions

Aquifer systems in arid regions

(World Water Assessment Programme, 2006)

4

(5)

Renewable or non

Renewable or non--renewable ?renewable ?

5

Non-renewable groundwater

Huge storage volume

Very low renewal rate

Renewable

(6)

Groundwater in the hydrological cycle

6

Recharge

Gr o u n d wa ter

(7)

Vadose zone

Vadose zone

7

Definition

9

The depth-zone between

the

ground surface

and the

(8)

Question

Is the vadose zone equivalent to the unsaturated zone?

(9)

Physical characteristics of vadose zone

9

Groundwater

Capillary fringe (saturated)

Soil

Water Air

Pressure potential

－　0　＋

Wetting

Drying

Vadose zone Unsaturated

(10)

Role of vadose zone

1. to partition the

precipitation input into

recharge flux as output to groundwater body and

evapotranspiration flux as loss

2. to damp down the

temporal variability of the output

10 Precipitation

Evapotranspiration

(11)

Literatures

9Stephens, D.B. (1996): Vadose Zone Hydrology. Lewis Publishers, New York.

9Parlange, M.B., and Hopmans, J.W. (1999): Vadose

Zone Hydrology: Cutting Across Disciplines. Oxford

University Press, New York.

¾ Hydrology (e.g., Ward and Robinson, 1990; Brutsaert, 2006)

¾Soil physics (e.g., Hillel, 1980; Campbell, 1985)

(12)

Contents of this lecture

Phenomenological aspects of individual processes

9 Infiltration & percolation

9 Evaporation (from soil surface)

9 Transpiration (through plant)

Unique characteristics of groundwater recharge

9 Under humid climate

9 Under arid climate

Practical methods for measuring or estimating groundwater recharge

(13)

Vadose zone hydrological processes

Vadose zone hydrological processes

13 Precipitation

Evaporation Infiltration

Groundwater recharge Surface runoff

Percolation

(14)

Infiltration

&

Percolation

(15)

Terminology

Terminology

Infiltration

9Process of water entry into the soil across the ground

surface

Percolation

9Process of water penetration below the shallow

subsurface (e.g., root zone)

Infiltration capacity

9Maximum rate of infiltration for a given soil

¾It depends on soil hydraulic properties and varies with time during a storm event

(16)

Infiltration capacity

Infiltration capacity

16

Time

Initial infiltration capacity

(17)

Atmospheric control phase

17

Time

Rainfall intensity

(18)

Soil control phase

18

Time

Rainfall intensity

Infiltration

(19)

Final infiltration capacity

Final infiltration capacity

Land cover Final infiltration (mm/hr) n

Forest Coniferous (natural) Coniferous (artificial) Broad-leaved (natural) 211.4 260.2 271.6 5 14 15 Cutover area Slightly disturbed Heavily disturbed 212.2 49.6 10 5 Grassland Natural Artificial 143.0 107.3 8 6 Bare ground Collapsed Agricultural Paved 102.3 89.3 12.7 6 3 3 19

Examples of measured final-infiltration-capacity in Japan

(20)

Wetting front

Wetting front

20

Depth

Water content

Initial water content Saturated water content

0

(21)

Unstable wetting front

21

Ground surface

Fingering

(22)

Preferential flow

Unstable flow

¾ Fingering

Funneled flow

¾ Capillary barrier

Macropore flow

¾ Bypass flow

through rock fractures, cracks, and root tubules

22

(23)

Funneled flow

Funneled flow

23

Water content

Height above water table 0 0

Coarse sand

Fine sand

(24)

Macropore flow

24

(25)

Stemflow

Stemflow--induced infiltrationinduced infiltration

25

Gross rainfall

Throughfall

Stemflow

(26)

Zero flux plain

26

Depth

Matric potential

Hydraulic potential Depth

Saturation

Equilibrium

X

Saturation to dry

Dry & rewet

DZFP

CZFP

(27)

Seasonal cycle of ZFP

Seasonal cycle of ZFP

27

(28)

Percolation

28

(Zimmermann et al., 1967) 0 20 40

60 120 0 20 40 60 100 80

0 20 40

60 120 0 20 40 60 100 80 0 20 40

60 120 0 20 40 60 100 80

0 20 40

60 120 0 20 40 60 100 80

0 20 40

60 120 0 20 40 60 100 80 4 days 26 days

82 days 152 days

214 days

Percentage of D₂O (%)

Depth (cm)

Advection (Pinston-like flow)

+

(29)

Evaporation

from soil surface

(30)

Evaporation and soil wetness

Evaporation and soil wetness

30

Soil wetness

Evaporation rate

Dry

Wet

1

st

stage

2

nd

(31)

Atmospheric control phase

31

Soil wetness

Evaporation rate

Potential evaporation

Dry

(32)

Penman equation Penman equation 32 a n p

E

l

G

R

E

γ

+

∆

+

−

+

∆

=

Potential evaporation

Net radiation Soil heat flux

Psychrometric constant Slope of saturation vapor pressure curve

Latent heat for evaporation

Radiative term Aerodynamic term

vpd E

a

C

Ue

p

E

=

ρ

0

.

622

Air pressure

Density of air Bulk coefficient for evaporation

Wind speed

(33)

Soil control phase

Soil control phase

33

Soil wetness

Evaporation rate

Dry

(34)

Dry Surface Layer (DSL)

34

Turbulent diffusion

Dry surface layer Evaporation surface

Liquid transport Vapor transport

Atmosphere

Evaporation fl

ux

Molecular

(35)

Observed DSL

35

(36)

DSL in coarse textured soils

DSL in coarse textured soils

36

(37)

DSL in fine textured soil

37

Yamanaka et al. (2000)

(38)

Numerically simulated DSL

38

(39)

Dependence on soil hydraulic properties

39

Sand

Loam Clay

Va po r

Liquid

Total

(40)

Effect of gravel mulch

Effect of gravel mulch

40

Turbulent diffusion

Molecular diffusion

Liquid water flow

Localized DSL

(41)

Question

Can evaporation occur directly from water table?

(42)

Evaporation from shallow water table

42

Hydraulic potential Depth

Saturation degree

Water vapor density

Day

(43)

Effect of shallow water table

Effect of shallow water table

43

(44)

Transpiration

through plants

(45)

Transpiration and root water uptake

Transpiration and root water uptake

45

Stomata

Transpiration

Root water

(46)

Two phases of transpiration process

46

Soil wetness

Evaporation rate

Dry

Wet

1

st

stage

2

nd

stage

Bare

soil e vapo

ration

Trans pir

(47)

Soil

Soil--PlantPlant--Atmosphere Continuum (SPAC)Atmosphere Continuum (SPAC)

47 Transpiration Evaporation R_interface R_soil R_root R_stem R_stomata 0 20 40 60 80 100 120 140 160

0 200 400 600 800 1000

De

p

th

cm

(48)

Uptake: low transpiration rate

48 0 20 40 60 80 100 120 140 160

0 5 10 15

De p th cm Relative uptake % 0 20 40 60 80 100 120 140 160

‐4000 ‐3000 ‐2000 ‐1000 0

Matric potential

cm H₂O

(49)

Uptake: medium transpiration rate

49 0 20 40 60 80 100 120 140 160

0 5 10 15

‐4000 ‐3000 ‐2000 ‐1000 0

cm H₂O

(50)

Uptake: high transpiration rate

Uptake: high transpiration rate

50 0 20 40 60 80 100 120 140 160

0 5 10 15

‐4000 ‐3000 ‐2000 ‐1000 0

cm H₂O

(51)

Mechanism of phase switching

51

Transpiration

Evaporation

ψ_leaf

ψ_soil1

ψ_stem

ψ_soil2

ψ_soil3

(52)

Water use strategy by plants (1)

9 Non-streamside young trees

¾ Precipitation

9 Streamside young trees

¾ Stream water

9 All Mature trees

¾ Groundwater

9 Mature trees do not use

stream water even though they inhabit at stream side

9 Stream water is unstable

water resource

Mature (all)

Young

(streamside)

Young (non-streamside)

Riparian trees in semi-arid land

52

(53)

Deep rooted Shallow

rooted

Trees

Shrubs

9 Trees

¾ Summer rain

9 Shrubs

¾ Groundwater

9 Water uptake zone

corresponds root depth

9 Co-occurring plant species

utilize different water sources

Tree-shrub community in semi-arid land

53

(54)

-14 -12 -10 -8 -6 -4

1-Jun 2-Jul 2-Aug 2-Sep 3-Oct

2003

δ

18 O ( o /oo

)

Soil water 10cm Soil water 20cm Soil water 40cm Soil water 80cm Groundwater P. densiflora Q. myrsinaefolia Understory

54

(55)

Water source separation

P. densiflora

Q. myrsinaefolia

Understory

(56)

Hydraulic lift

Day

Night

(57)

Evidence of hydraulic lift

57

(58)

Inter

Inter--specific interaction through hydraulic liftspecific interaction through hydraulic lift

9 Herbaceous plants benefit from big tree through hydraulic lift !

Distance (m) 0.5 1 1.5 2.5 5

δD (‰)

(59)

Competition for water

9 Competition may overwhelm facilitative effects of hydraulic lift !

Trenching treatment Control

Growth of grasses

Low High

59

(60)

Role of plants in recharging groundwater

Positive role

¾ Water supply through stemflow-induced infiltration

Negative role

¾ Water loss through transpiration

(61)

Groundwater recharge

under humid climate

(62)

Typical rates under humid climate

Typical rates under humid climate

Reference Location Soil Recharge (mm/yr) Precipitation (mm/yr) Recharge/ Precipitation Shimada (1983) Kanagawa,

Japan Loam 913 1670 0.55

Kayane et al. (1980)

Tokyo, Japan

Loam

885 1550 0.57

Ibaraki, Japan

Loam

399 1321 0.30

Hiroshima,

Japan Sand 523 1262 0.41

Anderson &

Sevel (1974) Denmark Till 358 780 0.46 Allison et al.

(1974) Australia Sandy loam 40-140 750 0.05-0.19 Sukhija &

Shah (1976) India Sand, loam 15-56 700 0.02-0.08 Vogel et al.

(1974) South Africa Sand 10 500 0.02

(63)

Sandy soils

Sandy soils

63

8 9 10 11 12 1 2 3 4 5 6 7

-100 0 100 200 300 400 500 600 Cu m rative i n filt ration flux (mm) 0 cm 5 cm 10 cm 20 cm 30 cm 50 cm 80 cm 1999 2000

8 9 10 11 12 1 2 3 4 5 6 7

-4 0 4 8 12 16 Monthl

y mean wate

r flux (mm/d)

P ET I

1999 2000

(64)

Loamy soil

64

M

W

Precipitation

Evapotranspiration

(65)

Effect of storm event

65

(66)

Multiple recharge sources

66 Interruption

of river

Infiltration

of precipitation

Infiltration of paddy water

Revival

of river Springs

(67)

Recharge at alluvial fan

67

Effluent seepage from river Infiltration from paddy

(68)

A case of Nasu fan, Japan

68 Sabi R.

Houki R.

Naka R. g1

g30 g3 g31 g7

g4 g5 g6

g44 g45

5km A

B

Ground surface

Water table

H z

(69)

How to evaluate contribution ratio

How to evaluate contribution ratio

69 ) )( ( ) )( ( ) )( ( ) )( ( d p d r d p d r d p d g d p d g r C C c c c c C C C C c c c c C C R − − − − − − − − − − = ) )( ( ) )( ( ) )( ( ) )( ( d r d p d r d p d r d g d r d g p C C c c c c C C C C c c c c C C R − − − − − − − − − − = p r

d R R

R =1− −

Contribution of river water

Contribution of precipitation

(70)

Estimated contribution ratio

70 g1 g30 g3 g31 g7 g4 g5 g6 g44 g45 Otawara 5 km Naka River Kuma River Sabi River Houki River Paddy-field water Precipitation River water 400 300 200 400 400

Wakui and Yamanaka (2006)

Distribution of paddies

(71)

Possible changes in future

Possible changes in future

Climate change effects

9Changes in precipitation and air temperature (via

potential evapotranspiration) affect groundwater recharge

9Vegetation change due to climate change may slightly

affect groundwater recharge

Human impacts

9Land use/cover change remarkably modify

groundwater recharge

9Water use also affects recharge amount and its

distribution

(72)

Change in temperature

Change in temperature

72 AR4-WG1_Figure 10.5. Time

series of globally averaged (left) surface warming (surface air temperature change, °C) and (right) precipitation change (%) from the various global coupled models for the scenarios A2 (top), A1B (middle) and B1 (bottom). Numbers in parentheses following the scenario name represent the number of simulations shown. Values are annual means, relative to the 1980 to 1999 average from the corresponding 20th-century simulations, with any linear trends in the

corresponding control run simulations removed. A three-point smoothing was applied. Multi-model

(73)

Change in precipitation

Change in precipitation

73

2080s mean － 1961-1990 mean SRES GCM change fields The IPCC Data Distribution Center

-2.25 -1.75 -1.25 -0.75 -0.25 0.25 0.75 1.25 1.75 2.25 (mm/d)

180 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180

(74)

Groundwater recharge

under arid climate

(75)

Typical rate under arid climate

Typical rate under arid climate

75

0 100 200 300 400 500

Precipitation (mm yr-1₎

0 50 100 600

Pe

rcolation (mm y

r

-1 )

sinkhole

sand dune

sand dune sand dune

fractured rock

playa lysimeter

crater

With vegetation Without vegetation

(76)

Example of Mongolian grassland

76

0 40 80 120 0 40 80 120 MGS 0 40 80 120 Cum u la ti ve wate r flux (mm) 0 40 80 120 Water s torage (mm) DGS 0 40 80 120 0 40 80 120 DRS

1-Jun 1-Jul 1-Aug 1-Sep

2001 -40 0 40 80 120 0 40 80 120 BTS

(77)

Evaporation, soil moisture and vegetation

Evaporation, soil moisture and vegetation

77 0 40 80 120 160 5 10 15 20 25 MGS 0 40 80 120 160 Ene rgy fl ux (W/m 2) 0 2 4 6 8 Volum e tr ic wa ter c o n tent (% ) DGS 0 40 80 120 160 4 8 12 16 20 DRS

1-Jun 1-Jul 1-Aug 1-Sep

2001 -40 0 40 80 120 160 0 4 8 12 16 BTS

lE θ3

0 0.1 0.2 0.3 0.4

Vegetation cover (m2/m2)

0 5 10 15 ∆lE / ∆

θ(W 3

(78)

Question

In spite of negligibly small recharge, why can people use groundwater ?

(79)

Two modes of groundwater recharge

Two modes of groundwater recharge

Distributed recharge (or diffuse recharge)

9Continuously occurring over widely distributed,

normal land covers

¾i.e., grassland, forest, agricultural land, etc.

Concentrated recharge

9Transiently occurring at a limited, specific areas

¾i.e., wadi, playa, fractured rock outcrop, etc.

(80)

Temporal variability of precipitation

Temporal variability of precipitation

80

1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990

Year 0 10 20 30 40 50 Re ch a rge (mm /y r) 800 600 400 200 0 Rainfall (mm/y r)

(81)

Future change in rainfall intensity

81

(Kimoto et al., 2005)

No-rain days Moderate-rain days (1-20 mm/d)

(82)

Possible changes in future

Climate change effects

9Changes in not only precipitation amount but also

precipitation pattern (e.g., intensity, frequency, duration) remarkably affect groundwater recharge

9Vegetation change due to climate change also affects

recharge amount

¾Increase in precipitation enhances vegetation growth with more evapotranspiration, introducing no change in

groundwater recharge?

Human impacts

9Human activities except for agricultural land/water

use may less affect groundwater recharge

(83)

Practical methods

for measuring or estimating

groundwater recharge

(84)

1. Water balance method

1. Water balance method

84

P _E

T

∆S

G_R

G

_R

= P – E

_T

–

∆

S

Advantage:

¾ Accurate under humid climate

¾ Areal average

Disadvantage:

¾ Relatively expensive

¾ less-accurate under arid climate

(85)

Measurement of precipitation

(86)

Measurement of evapotranspiration (1)

Eddy correlation method

86

q

w

(87)

Measurement of evapotranspiration (2)

Measurement of evapotranspiration (2)

Energy balance/Bowen ratio method

87

(

n _o

)

T

B

l

G

R

E

+

−

=

1

(

)

(

q

₁1

q

₂2

)

l

T

c

B

_o p

(88)

Measurement of soil water storage change

Methods to monitor soil water content

¾TDR (Time Domain Reflectometry)

¾TDT (Time Domain Transmissivity)

¾FDR (Frequency Domain Reflectometry)

¾ADR (Amplitude Domain Reflectometry)

¾Heat probe method

¾Neutron probe method

(89)

2. Darcian flux method

2. Darcian flux method

89

Advantage:

¾ Simple

¾ Cheap

Disadvantage:

¾ Non-applicable under arid climate

¾ Less accurate

9 difficulty in estimating K

9 spatial heterogeneity

(90)

3. Lysimeter method

90

Advantage:

¾ Direct

¾ Applicable for various climates

¾ Disadvantage:

¾ Expensive

¾ Disturbed

9 soil

9 vegetation

(91)

4. Tracer method

4. Tracer method

91

Advantage:

Disadvantage:

¾ Sometimes uncertain

9 spatial heterogeneity

9 macropore flow

9 time scale

(92)

5. Chloride mass balance method

92

Advantage:

¾ Relatively cheap

Disadvantage:

¾ Uncertainty

9 chloride deposition rate

9 potential chloride source

9 Lateral advection

g p r

C

P

G

=

⋅

p