field estimation of wetland soil saturated hydraulic conductivity peter caldwell ssc570 12/2/03
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Field Estimation of Wetland Soil Saturated Hydraulic Conductivity Peter Caldwell SSC570 12/2/03. Causeway Bay. Agenda. Background The Bouwer-Rice Method Field Procedures Office Procedures Results Conclusions. Background Hydrology Modeling. - PowerPoint PPT PresentationTRANSCRIPT
Field Estimation of Wetland Soil Saturated Hydraulic Conductivity
Peter CaldwellSSC57012/2/03
Causeway Bay
Agenda Background The Bouwer-Rice Method Field Procedures Office Procedures Results Conclusions
BackgroundHydrology Modeling
Research project involves modeling the hydrology of three Carolina Bays
Each bay has 4-7 wells used to collect data for model calibration
Each well location will be modeled Model requires Ksat of all soil layers to 1 m
depth
BackgroundReference Bays
Charlie Long Bay
Tatum Millpond Bay
Causeway Bay
Bladen County, NC
The Bouwer-Rice Method Slug test method to determine Ksat in-situ
Only works at depths below water table
The Bouwer-Rice Method
Ground Surface
Impermeable Layer
Unsaturated Soil
Saturated Soil
Soil at Field Location
The Bouwer-Rice Method Bore a hole to desired depth
The Bouwer-Rice Method Insert well casing and screen
The Bouwer-Rice Method Drop in slug
The Bouwer-Rice Method Record height of water in tube vs. time
H
H vs. time
0.001
0.01
0.1
1
0 5 10 15 20 25 30
t (sec)
log
H (
m)
The Bouwer-Rice Method Calculate Ksat
t
o
e
wc
H
H
tLr
rK ln
1
2
Rln
e2
H
h Lw Le
2rc
2rw
Where,
A and B are dimensionless parameters based on Le/rw
Note: Use straight line portion of graph of H vs. time for t, Ho, Ht
1
eln
ln
1.1Rln
we
w
w
www
rL
rLhBA
rLr
Field ProceduresField Conditions
Thick
Field ProceduresField Conditions
Deep
Field ProceduresEquipment- Well Casing
4” PVC Pipe with holes drilled in lower 20 cm
Holes less likely to get clogged than slots Duct tape allowed fine tuning of screen
length
Field ProceduresEquipment- slug
Slug 2” PVC, 24” long Filled with gravel
Field ProceduresEquipment- Level-logger
Level-logger Made by Solinst Records height of
water above logger Records every 0.5
second
Field ProceduresProcedure
Wanted Ksat values for all soil horizons to a depth of 1 m
Had soil profile descriptions from previous study Depths/Thicknesses Texture
Field ProceduresProcedure- Augering Hole
Based on profile descriptions, tape screen to appropriate length
Auger through root mat Set well casing into hole created Auger inside casing Push casing down Repeat until screen is positioned at
desired depth
Field ProceduresProcedure- Insert Level-logger
Wait until water inside casing equalizes with water table
Drop level-logger inside casing
Field ProceduresProcedure- Inserting Slug
Wait 2-3 minutes for water to equilibrate from level-logger drop
Insert slug smoothly but quickly
Field ProceduresProcedure- Wait
Allow time for water level to lower (usually 10-15 minutes)
Approximately long enough for one game of crazy eights
Field ProceduresProcedure- Download data
Field ProceduresProcedure
Performed procedure 3 times for each horizon
Auger down to next horizon Repeat procedure for remaining horizons Repeat for each well location
Office Procedures
Compile H vs. time data for each horizon Fit straight line for points on curve Calculate Ksat
Office ProceduresH vs. Time data
CL1 Horizon 3Falling Water Table
0.1
1
10
100
0 10 20 30 40 50 60
Time (sec)
Wa
ter
Le
ve
l (c
m)
Trial 1Trial 2
ResultsKsat Values for Various Textures
fibric (8)51 172 479
hemic (5)41 76 125
sapric (9)6 81 460
mucky sandy loam (5)11 24 49
mucky loamy sand (6)64 147 263
mucky sand (1)20
sandy loam (1)10
loamy sand (3)58 83 109
sand (9)14 195 245
So
il H
ori
zon
Typ
e
450 500
Ksat (cm/hr)
50 100 150 200 250 300 350 400
Ksat Values for Various Soil Types in Reference Carolina Bays
ResultsKsat Vs. Depth by Soil Type
MineralOrg Depth < 20 cm
0
100
200
300
400
500
0 20 40 60 80 100
Depth (cm)
Ks
at
(cm
/hr)
CL1
TM1A
CW1
HisticOrg Depth = 20-40 cm
0
100
200
300
400
500
0 20 40 60 80 100
Depth (cm)
Ks
at
(cm
/hr) CL2
CL3
TM2
CW2
Shallow OrgOrg Depth = 40-80 cm
0
100
200
300
400
500
0 20 40 60 80 100
Depth (cm)
Ks
at
(cm
/hr) TM2A
TM3
CL4
CW3
Deep OrgOrg Depth > 80 cm
0
100
200
300
400
500
0 20 40 60 80 100
Depth (cm)
Ks
at
(cm
/hr) TM4
TM5
TM6
CW4
Conclusions
Slug test method was a relatively simple and straightforward method to estimate Ksat
Ksat values were reasonable, though slightly high
Will run further tests to validate the results