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Examining Vertical Stability of Deep Rod Marks in Marshes

Examining Vertical Stability of Deep Rod Marks in Marshes. Philippe Hensel 1 , James Rassman 2 , Jordan Mora 2 , Chris Weidman 2 , James Lynch 3 , Christine Gallagher 1 , Jarir Saleh 1 and Donald Cahoon 4 1 NOAA National Geodetic Survey

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Examining Vertical Stability of Deep Rod Marks in Marshes

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  1. 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 Survey 2 Massachusetts Department of Conservation and Recreation, Waquoit Bay National Estuarine Research Reserve 3 National Park Service Northeast Region 5 US Geological Survey, Patuxent Wildlife Research Center

  2. Problem Statement 1 • Wetland elevation change data using Surface Elevation Tables (SETs) rely on in situ vertical reference marks.

  3. 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)

  4. 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?

  5. 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 T3 T2 Railroad Bed Patuxent River T4 T1 Low intertidal SETs T5 High intertidal SETs Railroad Bed Tide station

  6. 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 T3 T2 Railroad Bed Patuxent River But we have SET marks! T4 T1 Low intertidal SETs T5 High intertidal SETs Railroad Bed Tide station Can SET marks be used for vertical control?

  7. 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?

  8. 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

  9. 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

  10. 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

  11. 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?

  12. Waquoit Bay NERR • Deep peat soils (300 feet?) • Need to develop local vertical control network • Local interest

  13. 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)

  14. Results All methods significantly different at P  0.02 125.5’ 92.8’ 63.3’ n = 3 n = 3 n = 3

  15. 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

  16. Surveying in the Marsh

  17. Leveling Statistics • 90% of section misclosures  0.5 mm • 70% of loop misclosures  0.5 mm

  18. Results

  19. 2001 3001

  20. NGS Mark 555

  21. Few sections show significant trends

  22. 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?

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