Thad Wester
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Pea Island, Study Site #2

4/19/2011

7 Comments

 
Picture
Houses near Nags Head, NC
Currently, the Outer Banks is witnessing significant rates of beach erosion, most of which is a function of sea level rise.  In opposition to popular reporting, sea level rise and fall are a natural phenomenon which have been continuing for millennia.  Currently we are in a period of sea level rise (Riggs and Ames 2003), the rate of which (most scientist agree) has been increased by human influenced global climate change (Gornitz et al. 1982).  On the Outer Banks the effects of sea level rise are compounded by land subsidence from glacial isostatic adjustment.  In fact, due to the local influence of land subsidence the Outer Banks could be experiencing a 60% greater rate of relative sea level rise in comparison to the national average of the United States (Cabanes et al. 2001).

In March, 2011, I traveled to the Pea Island national wildlife refuge to terrestrial laser survey a section of overwashed dune in an attempt to establish a long term overwash monitoring site within the Cape Hatteras National Seashore.  As I have detailed previously, overwash is an important aspect of barrier island landward migration and thus an important area of research along the Outer Banks, which is a barrier island. This is especially true if you also consider the amount state owned infrastructure and privately owned houses which are currently impacted or have the potential to be soon impacted by barrier island landward migration.


Methods

Picture
View of target and scanner setup from the behind the dune.
Two Leica C10 terrestrial laser scanners and eight Leica HDS targets were employed in the survey of a 150m wide stretch of overwashed dunes.  13 separate scans were made at the resolution of 2.5cm at 30m, collecting 140 million survey points in 10 hours. Registration error between the surveys was 0.002 meters.  For repeat surveys at the site, 2 foot lengths of steel re-bar were driven into the ground below each of the targets, constituting target monuments.

In addition to the laser scan survey, a RTK-GPS base station and rover unit provided: a coarse resolution survey of the site for comparison with laser scan data; ground-truthing in areas of dense vegetation; and geo-referencing capabilities for the laser scan survey.

Picture
A 360 degree panorama of the study site, as viewed from the front and center of the overwashed dunes.

Discussion

Laser scanning terrain which has dense vegetation reduces the quality of data and increases post processing time greatly. Here, I am trying to solve these problems by using an RTK-GPS and a ground finding algorithm.
GPS points were surveyed in areas where the vegetation was too dense for the laser scanner to penetrate.  The laser scanned vegetation points will then be replaced by the GPS points producing a more accurate digital terrain model than is possible by only using laser scanning or GPS by themselves. 
Cyclone TOPO II has a ground finding function which climbs from point to point and classifies points as ground, or non-ground points (it deletes the points), based on their elevation in relation to surrounding points. A digital terrain model free of vegetation is currently being processed...

References
Cabanes et al. “Sea Level Rise During the Past 40 Years Determined from Satellite and in Situ Observations.” Science 294 (2001): 840-842.

Gornitz, V., S. Lebedeff, and J. Hansen. “Global Sea Level Trend in the Past Century.” Science 215.4540(1982): 1611-1614.

Riggs, Stanley R., and Dorothea V. Ames. Drowning the North Carolina Coast: Sea Level Rise and Estuarine Dynamics. Raleigh: North Carolina Sea Grant, 2003.
7 Comments
Dale Swiggett link
1/30/2012 03:01:30 am

Call it like it is, the PCS Mine is causing the Subsidence out 100 miles from Aurora,NC. by dewatering the Castle hayne and the Pee Dee Aquifers.

Send the bill for the of damages to I- 95 Hwy 12,,64,& 264 in NC, & Hwy 58 in Va. and the Bonner Bridge to PCS. PCS is putting over 20 billion dollars of real estate values, toursim revenues and 342,000 tourism jobs at stake from Va.- GA. Beverly Perdue is under fire and not running because her association with PCS and the Swiggett vs PCS Law Suit. Tens of Billions are at risk with PCS moving to Saudi Arabi, leaving the cost of damages to the US Taxpayer and perment damage to the Environment!

Dale Swiggett
NC State and US Federal "Qui Tam" Whistle Blower
336-340-6299

Reply
Thad
1/30/2012 03:19:16 am

And what does that have to do with barrier island migration and beach erosion?

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Dale Swiggett link
12/27/2012 11:13:03 pm

--------------------------------------------------------------------------------
The Land is Sinking Faster than the Water is Rising Thad!
Dale Swiggett
The Environmental Investigation Coalition
--------------------------------------------------------------------------------

Water subsidence due to east coast phosphate mining. This was sent by an elist member who has followed the activities of the PCS (Canadian phosphate mine in NC). Looks like a heads up for VA. km
As evidenced by multiple USGS reports, over pumping of groundwater sources such as aquifers causes land to sink (known as subsidence) and causes water quality problems as well as private wells have failed and has limited water availability to surrounding communities.
The USGS reports confirm the contamination of groundwater and salt water intrusion altering the depth of our waterways has harmed families’ small businesses dependent upon the Blue Crab and commercial fishing. The subsidence poses a growing threat to the motorcycle nation that travels along the roadways adversely affected by subsidence, as well as bridges such as the Bonner Bridge.
The PCS is adversely affecting a large geographical area from Sneads Ferry, NC to Virginia Beach, VA that has been covered up since 1967. Enclosed links confirm componding effects that the land is sinking faster than the water is rising.
Here are the links for USGS reports.....http://sc.water.usgs.gov/projects/gwavailability/
http://water.usgs.gov/ogw/pubs/fs00165/
http://www.ncwater.org/Permits_and_Registration/

Reply
Mia Evans link
1/17/2023 10:47:39 pm

It's interesting to know that an important part of a barrier island is also the overwash areas which is why getting it surveyed with laser levels systems will be useful. It seems that other survey processes aside from homeowners' needs are also vital to ensure that the piece of land will be used properly. In that case, I should ask professionals when I have bought a piece of land myself or even before purchasing one to make the best decisions for my savings.

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    Thad Wester

    Founder @ Clarity Scanning.  Lead the WeWork Reality Capture team.  Likes tennis, ping pong and college football.

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