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Home arrow Authors   The American Surveyor     

Surveying Louisiana Print E-mail
Written by J. Anthony Cavell, LS   
Sunday, 29 February 2004

A 5.553Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

The story of Louisiana is like good gumbo: the main ingredient is New Orleans, the roux is the Mississippi River, and whatever goes in after that is up to the cook.

Surveying in Louisiana takes on as many flavors as there are recipes for gumbo. Where else might a surveyor have to subdivide section 103 in a GLO surveyed township? Or use long bamboo in saltwater bays to mark the limits of oyster leases using a 1' transit, with sights on the horizon for location taken from quad maps? In the southern part of the state one's initiation to a field crew likely includes taking cross-sections of a bayou or canal, egged on at least until the water is breast deep. In the north one might spend time finding a pine knot or sifting ashes of below-ground stumps to identify a section corner.

Ingenious techniques and technologies were developed when scientific research demanded new information, when oil exploration required accurate and timely location of geologic information, and when pipeline companies needed to purchase and follow rights of way. Louisiana's history of land claims by Europeans dates back to the early 16th century. Alvarez de Pineda discovered the mouth of the Mississippi River in 1519. Perhaps the first surveyor was 1541 Hernando De Soto, who led the first group of white men to travel down the Mississippi River to the Gulf of Mexico in 1543. The first survey for speculators was done by French Canadians Pére Jacques Marquette, S.J., and Louis Joliet who followed the grande riviéré to its mouth in 1673 and established that it emptied into the Gulf of Mexico. This, in turn, led to the immediate formation of plans by the Canadians for settlement of the Mississippi Valley. Robert Cavalier, Sieur de la Salle, erected a cross at the mouth of the Mississippi River after descending the Mississippi from the Great Lakes claiming and naming the territory for Louis XIV in 1682. That's 485 years of surveying in Louisiana! (Figures 1 and 2)

Ten flags have flown over Louisiana and land rights often originate with Spanish, French, English or American grants. Each brought various customs of measurement and description, from the arpent and vara to the French foot and description in ' (foot) " (inches) and "' (lines). The importance of water traffic can be seen in many of the grants and claims that tend to be longer than they are wide as they radiate from the rivers, lakes and bayous. The Surveyor General instructed his deputies to survey radiating sections along navigable streams before dividing the remaining land into square sections. The surveyors were further instructed to plot all approved private grants before surveying public lands. Most of the grants had been surveyed privately and the claims followed natural boundaries or adjoiners so their rights were easily recognized. Not all the public lands were surveyed, particularly those in the swampy or marshy areas, which still results in many court disputes to court between land owners and the state where oil is involved, especially concerning rights to land underwater that is not shown as such in original plats. (Figures 3, 4 & 5).

Surveying, especially in the southern portions of Louisiana, often involves water. The largest North American freshwater swamp is the Atchafalaya Swamp that lies in between Baton Rouge and Lafayette. The delta created by the Mississippi River forms the toe of the boot. Saltwater marsh makes up much of the coast inland from the Gulf. Precise positioning in these conditions requires ingenuity. On the moving platform of a small boat, often the best proof of a line laid straightly is had by sighting the "picket fence of flagged poles placed between PIs.

Radios were mandatory as soon as they were small enough to carry into the boat. Most positioning or surveying in these conditions involved triangulating with two transits set up someplace solid calling angles to the Party Chief on the spot in the boat. Modern theodolites with compensators were too motion-sensitive to be useful. Many oil wells were spotted and pipelines laid in this way. As oil exploration left the inland marshes and ventured offshore into the Gulf of Mexico, these same techniques were applied. As the wells went further out, the surveyors moved to the tops of buildings on the beach or built scaffolds. When they went further still, pilings were driven and surveyed in then occupied by the surveyors to see out even further. Eventually, with permanent platforms constructed, points on the platforms were surveyed and occupied as control points.

South Louisiana surveyors were among the first to make use of EDMs. In the marsh, and particularly offshore, there was often a haze that could frustrate an observer looking through a transit telescope. What he could see with the naked eye was invisible through his instrument. Many positions were shot using a crude version of heliotrope to flash each other. Using the platform's control points, each instrument man would aim his instrument to a good estimate of where the other should be. Then, taking turns, they would flash sunlight along the axis of the telescope which was more easily seen and measured. All too often, however, even this trick wouldn't work, which would mean a delay until conditions improved, possibly at night when they could shoot lights.

This led to the development of microwave ranging. Whenever conditions became marginal, the surveyor would leave his transit and fire up his Autotape or one of the other EDM devices. Then by twirling knobs, and later reading indicators, the ranges could be determined. When the range of these devices was insufficient, the ingenious surveyor would put two units in a plane and the mate for each at the points of interest, then fly across their line and note the minimum ranges, allow for altitude, and voila, he was on.

It was a natural progression of this drive and ingenuity that led John Chance and Associates to take one of the rejected ideas proposed for GPS and develop it into STARFIX the only privately owned satellite positioning system which they used successfully for several years before GPS became practical. STARFIX was awarded the U.S. Senate Innovation Award in 1989. Today several Louisiana firms are leaders in the development and use of GIS, LiDAR, SONAR and ROVs.

Morgan City and New Orleans are towns surrounded by levees. The F E MA finished floor elevation in much of New Orleans is -4 MSL! Looking up to watch huge freighters pass nearby above head level is an everyday experience in South Louisiana.

For many years it was observable that the Gulf has been pushing back the coastline. One public service announcement harkened, "We are losing a football field of coast every 20 minutes!" Louisiana serves as nursery for much of the world's fisheries and supplies huge amounts of seafood produce, almost all of which spawns, hatches, or is nurtured in Louisiana's swamps and marshes.

The easy first targets for blame for the shrinking coastline is the Corps of Engineers (for sending the millions of tons of river sediment off the continental shelf instead of the wetlands) and the oil companies (for canals and transportation across the marsh, aggravating saltwater intrusion). While these practices are damaging, they weren't understood as such when planned. The readjustment of the vertical network by NGS in the 1980s was sidetracked a tad by suggestions by Professor Mugnier of LSU, (then at U NO) who suggested, based on gravity data, that NGS should re-level some of Louisiana first. NGS did so, and discovered a nearly one foot reduction in the values published for bench marks in the Southeast Louisiana area! With that information, surveyors were faced with the terrible task of having to explain why someone's house had to be built a whole foot higher than his neighbor's house that had been built only a few months earlier.

This information and more led to increased awareness and research into the Gulf's encroachment and the realization that the problem wasn't a simple one. There was erosion, but it was too simple to just blame oilfield canals. There was also compaction, but again it was too simple to blame just the Corps for dumping the Mississippi's sediments. Louisiana has tectonic activity equal to that of California, but it is cushioned by all the "goo", and the deeper stuff is simply going down (subsidence), and bending like a springboard (flexure). The rate is often 12mm/yr and higher (6-10 inches per decade)! NGS reported to Congress that there are no reliable bench marks in south Louisiana!

With this information and help from NGS and support from Congress, LS U is now home to the Louisiana Spatial Reference Center (LSRC). Prominent there are Dr. Dokka and Professor Mugnier. Louisiana has also had the long time benefit of NGS State Advisor "Bob" Zurfluh who retired Dec. 31, 2003. The LSRC has begun constructing a network of CORS called GulfNet to span all of the state, starting on the south and working up from there. Louisiana surveyors are now regularly using these 21st century bench marks. NGS now accounts for the vertical velocity of many marks in Louisiana. (The author is presently engaged in some quality control surveys ultimately for the FEMA program to update the flood maps in Louisiana.) With the official proclamation that there are no reliable bench marks, the only contemporary references to the national control system are the CORS, so the decision to use substantial occupation times and processing using NGS OPUS service was made. Then, using the established TB Ms and RTK we move around and double shoot the samples. Those places not suitable for GPS, such as wooded areas, are shot conventionally using a total station from point pairs set with the RTK. The results have been gratifying so far.

Louisiana is known as Sportsman's Paradise, the Pelican State, the Bayou State, Creole State, and Child of the Mississippi. It's home to Mardi Gras, Tabasco, andouille, etouffees, sauce piquantes, cayenne pepper, crawfish, and the sounds of jazz, blues and zydeco. Her heritage exceeds all in diversity. It's fun to be a surveyor here, to deal in real history both recent and long past. Like good gumbo, words don't do it justice. You just have to taste it.

Tony Cavell is a land surveyor, consultant and speaker. Licensed in Louisiana, he manages the Louisiana office of ESP Associates, and enjoys presenting seminars.

A 5.553Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

 
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