Water Balance and the Influence of Soil Structural Changes on Final Covers for Landfill Closure
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Transcript of Water Balance and the Influence of Soil Structural Changes on Final Covers for Landfill Closure
School of Civil and Environmental Engineering
Life Impact The University of Adelaide
Water Balance and the Influence of Soil
Structural Changes on Final Covers for Landfill
ClosureMelissa Salt, University of AdelaideMark Jaksa, University of Adelaide
Jim Cox, CSIROPaul Lightbody, Tonkin Consulting
Slide 2
School of Civil and Environmental Engineering
Life Impact The University of Adelaide
Research Objectives
• Measure and compare the drainage to determine if phytocovers reduce drainage to the same extent as conventional covers
• Correlate changes in drainage patterns over time from the phytocover and conventional cover changes with changes in bulk density, soil water characteristic curve and permeability
• Assess the tendency for anthropomorphic soil to tend towards the natural profile of the borrow source or toward a new stable profile
• Determine the effect of changes in bulk density, soil water retention curve and permeability on the predictability of the water balance as estimated from pre-construction laboratory testing
Slide 3
School of Civil and Environmental Engineering
Life Impact The University of Adelaide
Water Balance
• P = ET + R + L + D + ΔS
WASTE
COVER
Precipitation (P)
Runoff (R)
Leachate
Drainage (D)
Lateral flow (L)
Soil moisture storage (S)
Evapotranspiration (ET)
Slide 4
School of Civil and Environmental Engineering
Life Impact The University of Adelaide
Methodology – Field Scale
• Precipitation - Weather station
• Runoff - Flow meters
• Drainage and lateral flow - Tipping bucket rain gauges
• Soil moisture content – MP406
• Soil suction – CS229
Drainage layerRoot barrier
Runoff collection
Drainage collection
Soil cover layer1.5 mm LLDPE geomembrane
Interim cover
Earthen berms
not to scaleMonitoring nest
Slide 5
School of Civil and Environmental Engineering
Life Impact The University of Adelaide
Slide 6
School of Civil and Environmental Engineering
Life Impact The University of Adelaide
Slide 7
School of Civil and Environmental Engineering
Life Impact The University of Adelaide
Slide 8
School of Civil and Environmental Engineering
Life Impact The University of Adelaide
Slide 9
School of Civil and Environmental Engineering
Life Impact The University of Adelaide
Slide 10
School of Civil and Environmental Engineering
Life Impact The University of Adelaide
Methodology – Small Scale
• 1 m x 1 m x 1.5 m deep
• Replicate conventional and phytocover from Adelaide, including plants
• Irrigation and measure drainage
• Destructively sample 1 box of each cover type every 6 months
• Analyse samples for bulk density, soil water characteristic curve and permeability
Slide 11
School of Civil and Environmental Engineering
Life Impact The University of Adelaide
Methodology – Core samples
• To measure any change in permeability or bulk density as a result of alternate saturation and then drying the soil layers proposed to use in the Adelaide A-ACAP trial.
• Prepared core samples at known bulk density of phytocover soil and clay barrier
• Wet using falling head permeability apparatus until saturated and hydraulic conductivity measured
• Dry in oven at 30 oC until equilibrated and observe shrinkage and cracking
• Repeat process
Slide 12
School of Civil and Environmental Engineering
Life Impact The University of Adelaide
Water Balance Modelling
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0 200 400 600 800 1000 1200
Days since modelling commenced
Volu
met
ric
moi
stur
e co
nten
t
0.1 m 0.5 m
1 m 1.5 m
Moisture content at depth through conventional profile over first 3 years modelled
Slide 13
School of Civil and Environmental Engineering
Life Impact The University of Adelaide
Water Balance – Adelaide Site
Water balance
Phytocover (mm/yr & %) Conventional (mm/yr & %)
1 m 1.5 m 2 m As placed Dried
P 515 515 515 515 515
I 117 (23) 123 (24) 123 (24) 103 (20) 125 (24)
ET 349 (68) 357 (69) 364 (71) 412 (80) 369 (72)
R 0.7 (0.1) 0.7 (0.1) 0.7 (0.1) 0.8 (0.1) 0.8 (0.1)
L 0 0 0 0.5 0
D 48 (9) 34 (7) 28 (5) 0.2 (0) 23 (4)
Slide 14
School of Civil and Environmental Engineering
Life Impact The University of Adelaide
Water Balance Predictions
0
20
40
60
80
100
1957 1962 1967 1972 1977 1982 1987 1992 1997 2002
Year
Runoff
(m
m)
0
200
400
600
800
1000
Rai
nfa
ll (m
m)
Conventional Phytocover Rainfall
Predicted annual runoff volumes when surface soil permeability is reduced by one order of magnitude
Slide 15
School of Civil and Environmental Engineering
Life Impact The University of Adelaide
Results – Adelaide Soil Moisture
0
5
10
15
20
25
30
35
40
31/10/2007 0:00
2/11/2007 0:00
4/11/2007 0:00
6/11/2007 0:00
8/11/2007 0:00
10/11/2007 0:00
12/11/2007 0:00
14/11/2007 0:00
16/11/2007 0:00
18/11/2007 0:00
Date and Time
Mo
istu
re c
on
ten
t (%
vo
l)
upslope 150 mm
upslope 700 mm
upslope 1350 mm
centre 150 mm
centre 700 mm
centre 1350 mm
downslope 150 mm
downslope 700 mm
downslope 1350 mm
RG201017
Slide 16
School of Civil and Environmental Engineering
Life Impact The University of Adelaide
Results – Adelaide Topsoil Moisture Content
0
50
100
150
200
250
300
350
400
450
500
17/07/20070:00
6/08/20070:00
26/08/20070:00
15/09/20070:00
5/10/20070:00
25/10/20070:00
14/11/20070:00
4/12/20070:00
Date and time
Cum
ulat
ive
Rai
nfal
l (m
m)
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
50.00
Soi
l moi
stur
e (%
vol
)
Rainfall Phytocover 150 mm Conventional cover 150 mm
Slide 17
School of Civil and Environmental Engineering
Life Impact The University of Adelaide
Results – Melbourne Soil Moisture
0
5
10
15
20
25
30
35
40
12/02/070:00
3/04/070:00
23/05/070:00
12/07/070:00
31/08/070:00
20/10/070:00
Date Time
Mo
istu
re c
on
ten
t (%
vol)
0
100
200
300
400
500
600
700
800
Cu
mu
lativ
e R
ain
fall
(mm
)
Phytocover 150 mm Phytocover 800 mm Phytocover 1550 mmConventional 150 mm Conventional 500 mm Conventional 850 mmCumulative Rainfall
Slide 18
School of Civil and Environmental Engineering
Life Impact The University of Adelaide
Outcomes
• Water balance comparison of phytocaps for Australian environment
• Variability of water balance predictions from selected models
• Quantification of soil structural changes in the short to medium term
• Impact of soil structural changes on sustainability of the phytocaps
• Determination of best soil input parameters for pre-construction modelling