methods for determining lateral effects of a borrow pit on … · 2017. 2. 14. · example 1 • a...
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Methods for Determining Lateral Effects of a Borrow Pit on Adjacent Wetlands
1-23-07
Lateral Effect
WetlandBorrow Pit
Water Table
h
h0-d
d
10 in.(25cm)@ T25
h0
d1
d2
Objectives:
• Develop information necessary to estimate thelateral effect of wetland hydrology.
• Survey existing (closed) borrow pits to determinefactors that might affect adjacent wetlands.
• Measure (record) water level rise after closure in5 borrow pits and W.T.E. in adjacent wetlands.
• Develop a model to predict water balance in pit.• Conduct workshops to teach use of the method
Example 1
• A borrow pit is to be excavated in a Goldsborosoil adjacent to a wetland.
• The depth of the pit will be 17 ft. with thebottom 15 ft below the surface of the wetland.
• Hydraulic conductivity of the soil is 2 in./hr andthe drainable porosity is 0.035.
• What setback distance is require to avoidhydrologic impacts to the wetland.
Lateral Effect
WetlandBorrow Pit
Water Table
h = 14.17’
h0-d
d = 13’
10 in.(25cm)@ T25
h0 = 15’
d1
d2
H= h/ho = 14.17/15 = 0.94D= d/ho = 13/15 = 0.87 vK/f ho t x = 1/?
K= 2 in./hr = 4 ft/d, f = 0.035 4 15 • 5.2v.035
1/?x = =
Example 1
=
Lateral Effect
WetlandBorrow Pit
Water Table
h = 14.17’
h0-d
d = 13’
10 in.(25cm)@ T25
h0 = 15’
d1
d2
H= h/ho = 14.17/15 = 0.94D= d/ho = 13/15 = 0.87 vK/f ho t x = 1.08
K= 2 in./hr = 4 ft/d, f = 0.035 4 15 • 5.2v.035
1.08x = = 88 ft
Example 1
Setback distance = 88 ft
Open Instrumented
ClosedClosed Instrumented
Open
Park L
Prime R
Vann
Pierce
Bullard 3
Mildred W
NanceBorden EVail
Aycock Hobbs
Borden S
Bullard 6
StallingsHardy
Bethel
Spruill
ThomasonTart
DavisAlex
Open Instruments Planned
Closed Instruments Planned
Bullard 4
Callie Rd
Twiddy
Location of Borrow Pits Surveyed
Table 1. Summary of Pit and wetland surface elevations
Name WSE Wetland ∆h (ft) Distance Pit (ft) Sur El (ft) from Pit (ft
Bordon E 4.43 5.64 1.21 98Bordon S 7.07 1.01 -6.06 176Bullard 4 1.26 5.05 3.79 70Bullard 6 tbi ? 5.74 8.13 2.39 315Callie Road 4.13 8.43 ? 4.2 125Hardy i 7.94 10.2 2.3 230Mildred Woods i 8.22 9.25 1.03 100Nance 5.33 1.77 -3.44 90Pierce 7.45 4.82 -2.63 156Stallings i 3.42 1.67 -1.75 100Tart 10.23 5.08 -5.17 267Twiddy tbi 2.52 2.5 0 127Vail tbi 13.3 6.24 -7 100Williams 2.89 5.6 2.7 112
28Total
7Unclear
9Pit to Wetland
12Wetland to Pit
NumberFlow Direction
Summary of survey of closed pits
Borrow Pit8.22 ft
9.25 ft
300 ft
Mildred Woods PitMay 3, 2005
100 ft
10.4 ft
9.82 ft8.98 ft
Borrow Pit8.02 ft
9.25 ft
300 ft
Mildred Woods PitAugust 3, 2005
100 ft
10.4 ft
7.74 ft 7.87 ft
Borrow Pit
5.74 ft
8.29 ft ~10 ft8.13 ft
315 ft
Bullard 6 Pit
295 ft 259 ft
175 ft
8.72 ft 9.61 ft
Borrow Pit4.13 ft
8.75 ft ~9 ft? ft
175 ft
Callie Road Pit
125 ft 25 ft
8.43 ft
Borrow Pit
13.27 ft
17.27 ft
6.42 ft1.15 ft
201 ft
Vail Pit
Borrow Pit
5.24 ft
9.06 ft
4.66 ft
122 ft
Alexander Pit
110 ft
127 ft
360 ft 233 ft
6.68 ft6.24 ft6.05 ft
Borrow Pit
7.07 ft17.27 ft
1.01 ft
176 ft
Borden South Pit
Borrow Pit
10.23 ft
20.10 ft
~14 ft
4.45 ft
377 ft
Tart Pit
297 ft 267 ft 177 ft
4.49 ft 5.08 ft
Borrow Pit
5.33 ft14.51 ft
1.77 ft
90 ft
Nance Pit
Wetland
Water Table
Borrow Pit
267-5.175.0810.23Tart
90-3.441.775.33Nance
156-2.634.827.45Pierce
176-6.061.017.07Borden S
100-7.06.2413.3Vail -tbi
100- 1.751.673.42Stallings -i
Dist.fromPit (ft)
? h (ft)WetlandEl (ft)
WSEPit (ft)
Name
Table 2. Summary for pits with flow from pit to wetland
Instrumented Borrow Pits,
(Closed > 2 Years)
400 ft
Pit water level100’ well300’ well
Ground elev. At 100’Ground elev. At 300’
Mildred Woods
5
6
7
8
9
10
11
100 200 300Day of Year
Rel
ativ
e E
leva
tion
(ft)
0102030405060708090100
Rain
Predicted Range 97 to 139 ft.
Mildred Woods Borrow Pit, Edgecombe County, 2005 - 2006
4
6
8
10
12
0 60 120 180 240 300 360 420 480 540 600 660 720Day
Rel
ativ
e El
evat
ion
(ft)
0
20
40
60
80
100
120
140
Ground at 100' Ground at 300' Pit Water LevelWell at 100' Well at 300' Rain
Cum
ulative Rain (in)
Mildred Woods Borrow Pit, Edgecombe County, 2005 - 2006
4
6
8
10
12
0 60 120 180 240 300 360 420 480 540 600 660 720Day
Rel
ativ
e El
evat
ion
(ft)
0
20
40
60
80
100
120
140
160
180
Ground at 100' Ground at 300' Pit Water LevelWell at 100' Well at 300' Rain
Cum
ulative Rain (in)
Hardy
Pitt County
Borrow Pit7.43 ft
10.4 ft
230 ft
Hardy PitAugust 16, 2005
115 ft
10.2 ft
6.84 ft 7.01 ft
Borrow Pit7.48 ft
10.4 ft
230 ft
Hardy PitOctober 9, 2005
115 ft
10.2 ft
8.78 ft 8.27 ft
Hardy
0
5
10
15
0 100 200 300
Day of Year
Rel
ativ
e E
leva
tion
(ft)
0102030405060708090100
Rain (in)
Pit water level115’ well230’ well
Ground elev. At 115’Ground elev. At 230’
Predicted lateral effect, 90 ft.
Hardy Borrow Pit, Pitt County, 2005-2006
0
3
6
9
12
0 60 120 180 240 300 360 420 480 540 600 660 720Day
Rel
ativ
e El
evat
ion
(ft)
0
20
40
60
80
100
120
140
Ground at 115' Ground at 230' Pit Water LevelWell at 115' Well at 230' Rain
Cum
ulative Rain (in)
Hardy Borrow Pit, Pitt County, 2005-2006
0
3
6
9
12
0 60 120 180 240 300 360 420 480 540 600 660 720Day
Rel
ativ
e El
evat
ion
(ft)
0
20
40
60
80
100
120
140
160
180
Ground at 115' Ground at 230' Pit Water LevelWell at 115' Well at 230' Rain
Cum
ulative Rain (in)
Stallings, Washington Co.
Borrow Pit
7.83 ft
10.6 ft
8.80 ft
5.71 ft
Stallings Pit
59 ft
75 ft
150 ft
117 ft
6.21 ft
Stallings
0
5
10
15
0 100 200 300Day of Year
Rel
ativ
e E
leva
tion
(ft.)
0102030405060708090100110120130140150
Rain (in)
Pit water level75’ well150’ well (creek edge)
Ground elev. At 75’Ground elev. At 150’
Predicted Lateral Effect, 149 ft..
Stallings Borrow Pit, Washington County, 2005 - 2006
0
2.5
5
7.5
10
0 60 120 180 240 300 360 420 480 540 600 660 720Day
Rel
ativ
e El
evat
ion
(ft)
0
20
40
60
80
100
120
140
160
180
Ground at 75' Ground at 150' Pit Water LevelWell at 75' Well at 150' Rain
Cum
ulative Rain (in)
Stallings Borrow Pit, Washington County, 2005 - 2006
0
2.5
5
7.5
10
0 60 120 180 240 300 360 420 480 540 600 660 720Day
Rel
ativ
e El
evat
ion
(ft)
0
20
40
60
80
100
120
140
160
180
200
Ground at 75' Ground at 150' Pit Water LevelWell at 75' Well at 150' Rain
Cum
ulative Rain (in)
Instrumented Borrow Pits,
(Recently Closed)
400 ft
Davis
Davis
0
5
10
15
20
25
0 100 200 300
Day of Year
Rel
ativ
e E
leva
tion
(ft)
0102030405060708090100110120130140150160
Rain (in)
Pit water level100’ well200’ well
Ground elev. At 100’Ground elev. At 200’
Predicted Lateral Effect 41 to 58 ft.
Davis Borrow Pit, Tyrrell County, 2005-2006
0
5
10
15
20
0 60 120 180 240 300 360 420 480 540 600 660 720Day
Rel
ativ
e El
evat
ion
(ft)
0
20
40
60
80
100
120
140
160
180
Ground at 100' Ground at 200' Pit Water LevelWell at 100' Well at 200' Rain
Cum
ulative Rain (in)
Davis Borrow Pit, Tyrrell County, 2005-2006
0
5
10
15
20
0 60 120 180 240 300 360 420 480 540 600 660 720Day
Rel
ativ
e El
evat
ion
(ft)
0
20
40
60
80
100
120
140
160
180
200
Ground at 100' Ground at 200' Pit Water LevelWell at 100' Well at 200' Rain
Cum
ulative Rain (in)
!(
!(
!(
200 f
t
200
ft
Prime Ridge
Prime Ridge West (wooded)
0
5
10
15
0 100 200 300
Day of Year
Rel
ativ
e E
leva
tion
(ft)
0102030405060708090100
Rain (in)
Prime Ridge West (wooded)
0
5
10
15
0 100 200 300
Day of Year
Rel
ativ
e E
leva
tion
(ft)
0102030405060708090100
Pit water level100’ well155’ well
Ground elev. At 100’Ground elev. At 155’
Pred. Lateral Effect 148 to 194ft (w/o sf)
Prime Ridge Borrow Pit, West Transect, New Hanover County, 2005 - 2006
0
4
8
12
16
0 60 120 180 240 300 360 420 480 540 600 660 720Day
Rel
ativ
e El
evat
ion
(ft)
0
20
40
60
80
100
120
140
160
180
Ground at 100' Ground at 155' Pit Water LevelWell at 100' Well at 155' Rain
Cum
ulative Rain (in)
Prime Ridge Borrow Pit, West Transect, New Hanover County, 2005 - 2006
0
4
8
12
16
0 60 120 180 240 300 360 420 480 540 600 660 720Day
Rel
ativ
e El
evat
ion
(ft)
0
20
40
60
80
100
120
140
160
180
200
220
240
Ground at 100' Ground at 155' Pit Water LevelWell at 100' Well at 155' Rain
Cum
ulative Rain (in)
Prime Ridge East (grassy)
0
5
10
15
20
0 100 200 300Day of Year
Rel
ativ
e E
leva
tion
(ft)
0102030405060708090100110120
Rain (in)
Pit water level100’ well200’ well
Ground elev. At 100’Ground elev. At 200’
Prime Ridge Borrow Pit, East Transect, New Hanover County, 2005 - 2006
0
4
8
12
16
0 60 120 180 240 300 360 420 480 540 600 660 720Day
Rel
ativ
e El
evat
ion
(ft)
0
20
40
60
80
100
120
140
160
180
Ground at 100' Ground at 200' Pit Water LevelWell at 100' Well at 200' Rain
Cum
ulative Rain (in)
Prime Ridge Borrow Pit, East Transect, New Hanover County, 2005 - 2006
0
4
8
12
16
0 60 120 180 240 300 360 420 480 540 600 660 720Day
Rel
ativ
e El
evat
ion
(ft)
0
40
80
120
160
200
Ground at 100' Ground at 200' Pit Water LevelWell at 100' Well at 200' Rain
Cum
ulative Rain (in)
Spruill
0
5
10
15
20
25
0 100 200 300
Day of Year
Rel
ativ
e E
leva
tion
(ft)
0102030405060708090100110120
Rain (in)
Pit water level100’ well200’ well
Ground elev. At 100’Ground elev. At 200’
Pred. Lat. Eff. 61 to 86 ft
Spruill Borrow Pit, Tyrrell County, 2005 - 2006
0
5
10
15
20
25
0 60 120 180 240 300 360 420 480 540 600 660 720Day
Rel
ativ
e El
evat
ion
(ft)
0
20
40
60
80
100
120
140
Ground at 100' Ground at 200' Pit Water LevelWell at 100' Well at 200' Rain
Cum
ulative Rain (in)
Spruill Borrow Pit, Tyrrell County, 2005 - 2006
0
5
10
15
20
25
0 60 120 180 240 300 360 420 480 540 600 660 720Day
Rel
ativ
e El
evat
ion
(ft)
0
20
40
60
80
100
120
140
160
180
Ground at 100' Ground at 200' Pit Water LevelWell at 100' Well at 200' Rain
Cum
ulative Rain (in)
Vann, New Hanover Co.
Borrow Pit
0.02 ft4.21 ft 4.18 ft
9.15 ft 9.98 ft 9.61 ft 9.79 ft
150 ft
15 ft 100 ft
150 ft
15 ft 100 ft
Vann Pit (early 2005)
Borrow Pit~6.0 ft
4.21 ft 4.18 ft
9.15 ft 9.98 ft 9.61 ft 9.79 ft
150 ft
15 ft 100 ft
150 ft
15 ft 100 ft
Vann Pit (late 2005)
Vann North (high ground)
0
5
10
15
20
25
0 100 200 300
Day of Year
Rel
ativ
e El
evat
ion
(ft)
0102030405060708090100110120130140150
Rain (in)
Pit water level100’ well200’ well
Ground elev. At 100’Ground elev. At 200’
Predicted Lat. Effect, 183 to 239 ft. w/o sf
Van Borrow Pit North Transect, New Hanover County, 2005 - 2006
0
5
10
15
20
0 60 120 180 240 300 360 420 480 540 600 660 720Day
Rel
ativ
e El
evat
ion
(ft)
0
20
40
60
80
100
120
140
160
180
200
Ground at 100' Ground at 200' Pit Water LevelWell at 100' Well at 200' Rain
Cum
ulative Rain (in)
Van Borrow Pit North Transect, New Hanover County, 2005 - 2006
0
5
10
15
20
0 60 120 180 240 300 360 420 480 540 600 660 720Day
Rel
ativ
e El
evat
ion
(ft)
0
40
80
120
160
200
240
Ground at 100' Ground at 200' Pit Water LevelWell at 100' Well at 200' Rain
Cum
ulative Rain (in)
Vann South (low ground)
0
5
10
15
20
0 100 200 300Day of Year
Rel
ativ
e E
leva
tion
(ft)
0102030405060708090100110120
Rain (in)
Pit water level100’ well200’ well
Ground elev. At 100’Ground elev. At 200’
Van Borrow Pit SouthTransect, New Hanover County, 2005 - 2006
0
4
8
12
16
0 60 120 180 240 300 360 420 480 540 600 660 720Day
Rel
ativ
e El
evat
ion
(ft)
0
20
40
60
80
100
120
140
160
180
200
Ground at 100' Ground at 200' Pit Water LevelWell at 100' Well at 200' Rain
Cum
ulative Rain (in)
Van Borrow Pit SouthTransect, New Hanover County, 2005 - 2006
0
4
8
12
16
0 60 120 180 240 300 360 420 480 540 600 660 720Day
Rel
ativ
e El
evat
ion
(ft)
0
40
80
120
160
200
240
Ground at 100' Ground at 200' Pit Water LevelWell at 100' Well at 200' Rain
Cum
ulative Rain (in)
What is the difference betweenwater level in pit and water level in
adjacent wetland?• Closed Pits with Measurements 13• Gradient from wetland to Pit 7 (3.3’)• Gradient from Pit to Wetland 6 (-4.2’)• Overall average difference
Wetland surface to pit water level -0.2’
Monitored PitsDifference in water level, wetland to pit (ft.)
• Mildred Woods © ~0• Hardy © 2• Stallings © - 2• Twiddy © ?• Davis ? (Waiting)• Prime Ridge -2 (W), +1 (E)• Spruil ? (waiting)• Vann -1 to -2 (S), +2 to 3 (N)
WetlandWetland
Water Table
WetlandWetland
Water Table
Borrow Pit
Summary
• Pits appear to fill to equilibrium in 1year or less
• Seepage is from pit to wetland inabout half of the cases
• Prediction method, as currently used,appears to overestimate lateral effectin most cases (probably because ofassumption of 2 ft depth)