Examining Vertical Stability of Deep Rod Marks in Marshes

Philippe Hensel1, James Rassman2, Jordan Mora2, Chris Weidman2, James Lynch3, Christine Gallagher1, Jarir Saleh1 and Donald Cahoon4

1 NOAA National Geodetic Survey2 Massachusetts Department of Conservation and Recreation, Waquoit Bay National Estuarine Research Reserve3 National Park Service Northeast Region5 US Geological Survey, Patuxent Wildlife Research Center

Problem Statement 1

• Wetland elevation change data using Surface Elevation Tables (SETs) rely on in situ vertical reference marks.

Problem Statement 1

• Wetland elevation change data using Surface Elevation Tables (SETs) rely on in situ vertical reference marks.

• SET marks have varied over the past decade (pipes, rods), as have their installation methods (by hand, vibracorer, impact hammer, jackhammer)

Problem Statement 1

• Wetland elevation change data using Surface Elevation Tables (SETs) rely on in situ vertical reference marks.

• SET marks have varied over the past decade (pipes, rods), as have their installation methods (by hand, vibracorer, impact hammer, jackhammer)

• Does installation method result in different vertical stability?

Problem Statement 2

• Sea level change “Sentinel Sites” rely on a high accuracy local vertical control network

• Vertical control networks hard to find in marshes

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Railroad Bed

Railroad Bed

Low intertidal SETsHigh intertidal SETsTide station

Problem Statement 2

• Sea level change “Sentinel Sites” rely on a high accuracy local vertical control network

• Vertical control networks hard to find in marshes

Railroad Bed

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T3

T4

T5

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Railroad Bed

Railroad Bed

Low intertidal SETsHigh intertidal SETsTide station

But we have SET marks!

Can SET marks be used for vertical control?

Problem Statement 2

• Sea level change “Sentinel Sites” rely on a high accuracy local vertical control network

• Vertical control networks hard to find in marshes

• Wetland elevation change study sites contain SET marks

• Can SET marks be used as part of local vertical control networks?

• How often should one re-establish vertical connections to maintain network integrity?

A short history of the SET

• 1980’s – research into vertical wetland processes and rates focuses on vertical accretion

• 1990’s – Developed technique to include accretion and erosion: the SET

A short history of the SET

• 1980’s – research into vertical wetland processes and rates focuses on vertical accretion

• 1990’s – Developed technique to include accretion and erosion: the SET

• 2000 – Adopted sectional rod monument type for SET mark

A short history of the SET

• 1980’s – research into vertical wetland processes and rates focuses on vertical accretion

• 1990’s – Developed technique to include accretion and erosion: the SET

• 2000 – Adopted section rod monument type for SET mark

• 2010’s – NGS introduces modifications to SET instrument and reference mark

SETs and Sentinel Sites

• SETs are now being used to monitor elevation change at sentinel sites

• Can older SET technology be used in conjunction with sentinel site infrastructure?

• What is the effect of installation technique?

• Does installation technique lead to differential stability?

Waquoit Bay NERR

• Deep peat soils (300 feet?)

• Need to develop local vertical control network

• Local interest

Study Design I

• NGS 3D rod marks reference marks– Compare insertion lengths among three techniques

• Manual hand held pile driver

• Bosch 11316EVS-type electric demolition hammer

• Gasoline-powered jackhammer

– One 3D rod mark per wetland section (3)

Results

63.3’

92.8’

125.5’All methods significantly different at P 0.02

n = 3 n = 3 n = 3

Study Design II

• 3D rod marks driven to known insertion lengths in wetland soil– 20 feet

– 40 feet

– 60 feet

– 80 feet

• Perform high precision digital barcode leveling among all marks to monitor relative stability

Surveying in the MarshRep Date Cumulative Days

0 Dec. 8-10 2011

1 Dec. 14-16 2011 6 days

2 Dec. 27-28 2011 20 days

3 Jan. 9-10 2012 33 days

4 Feb. 9-10 2012 64 days

5 Mar. 12-14 2012 95 days

6a May 30 – Jun. 1 2012 174 days

6b* Jul. 2012 229 days

7 Dec. 4-6 2012 362 days* Connecting Sections 1 and 2 only

Leveling Statistics

• 90% of section misclosures 0.5 mm

• 70% of loop misclosures 0.5 mm

Results

Spurious data connecting 3060 to 3001?

Potentially spurious data connecting 3060 to 3001

Possible error in section 3060 – 3001 (seen earlier)

Possible data error 3060 – 3001 on 12/28/2011

NGS Mark 555

Few sections show significant trendsSection: From To Coefficients Standard Error t Stat P-value R Square

2001 555 -0.211 0.176 -1.20 0.265 0.15

555 1001 -1.585 0.188 -8.45 0.000 0.90

1001 1060 1.468 0.392 3.74 0.002 0.50

1002 1001 -0.705 0.255 -2.77 0.015 0.35

1003 1002 -0.814 0.129 -6.29 0.000 0.50

1020 1040 0.049 0.300 0.16 0.872 0.35

1040 1003 0.683 0.868 0.79 0.444 0.04

1060 1080 -0.121 0.188 -0.64 0.530 0.03

1080 1020 -0.255 0.105 -2.42 0.030 0.30

2001 2040 -0.076 0.263 -0.29 0.775 0.01

2002 2001 -0.437 1.126 -0.39 0.704 0.01

2003 2002 -0.309 0.194 -1.59 0.134 0.15

2020 2080 -0.351 0.119 -2.94 0.011 0.38

2040 2020 -0.086 0.143 -0.60 0.556 0.03

2060 2003 0.367 0.222 1.65 0.121 0.16

2080 2060 -0.110 0.173 -0.64 0.534 0.03

3001 2001 -0.253 0.302 -0.838 0.416 0.05

3001 3002 0.045 0.376 0.12 0.908 0.00

3002 3040 0.075 0.107 0.70 0.493 0.03

3003 3020 0.001 0.443 0.00 0.997 0.00

3020 3080 -0.034 0.092 -0.37 0.716 0.01

3040 3003 0.257 0.212 1.21 0.246 0.09

3060 3001 -0.195 0.377 -0.52 0.614 0.02

3080 3060 0.035 0.165 0.21 0.835 0.00

Preliminary Conclusions

• Different rod insertion techniques yield significantly different insertion lengths

• No clear evidence of initial settling

• No clear trend in (in)stability among insertion lengths

• Apparent movement of all marks within a section the result of site-specific movements or epoch-based measurement biases?