A Changing Current
GPS technology helps locate river survey monuments
By Robert Keating

Topographic Land Surveyors of Oklahoma is using highly accurate GPS equipment for locating obscure survey monuments. These section boundary markers are needed for determining acreage of river tracts where oil and gas activity is present. Corners are particularly hard to find in rough terrain near the rivers. Many of the monuments located with GPS by TLSO's surveyors have been lost and unused for decades. The most valuable monuments recovered are those that were set by surveyors of the United States General Land Office (GLO) early this century.

Background and History
According to the laws of our nation and subsequent decisions by the courts, beds of non-navigable rivers generally belong to adjacent landowners. The adjacent landowner's boundary generally extends to the center (or medial line) of the river. Specific legal direction for river surveys is required because river boundaries are inherently different than non-river boundaries. Rivers, and therefore river boundaries, by nature are constantly changing in their location.
    For agricultural purposes there is seldom a need to incur the cost of a river survey. When the value of the land increases as it does with oil activity, acreage of each river tract must be determined as accurately as is possible.
    When the results of a survey are revealed, some landowners will have gained acreage from the movement of the river. Other landowners will have lost acreage. Landowners losing acreage have been known to challenge the results of a survey in court. The river survey must be performed to a high enough standard of accuracy and historical precedent to withstand legal challenge.
    In addition to challenges by individuals and companies, requirements of the United States government must also be considered. Much government-owned property is affected by river movement. Government tracts are leased to oil companies on the basis acreage determined by a current survey of the river. The government tracts administered through the Bureau of Land Management or the Bureau of Indian Affairs must be surveyed in a manner that meets their specific requirements.

Performing a River Survey
The first step in performing a river survey is to determine the existing upland boundaries. Corners for the sections through which the river currently flows and through which the river flowed at the time of the original General Land Office (GLO) survey must be determined. Real-time GPS has proven to be most helpful in this step.
    Determining section boundaries is complicated by the procedures used by the original surveyors. The early surveyors did not generally survey across rivers. The rivers were difficult to cross, so their surveys stopped at the river's edge. Different measurement errors accumulated as the survey crews traversed the sections and townships on opposite sides of the river. The surveys were performed at different times and had no ties to each other.
    A current survey of the river must begin by surveying across the river to connect the surveys on each side. In theory in Oklahoma, the connected sections should be a very regular pattern of square miles. In practice the results are often very irregular and skewed. Section lines across rivers are seldom straight. It is not unusual to find river sections with two locations of a single corner, such as two northeast corners or two southwest corners. Section lines may run at a thirty or forty-degree angle variation from expected north-south or east-west directions.

Monuments
As in all surveys of land boundaries, monuments set by the original surveyors are the controlling authority. To the land surveyor, original monuments are like gold. Due to the building of roads and other development projects through the years, many of the original survey monuments have been destroyed.
    Along rivers where there has been little development, some of the monuments can still be found. With GPS technology, surveyors at TLSO are locating boundary monuments more successfully. Newly recovered corner monuments are referenced and filed with the State of Oklahoma.

Using Real-Time GPS
GPS is the acronym for the Global Positioning System. This system was designed and implemented by the U.S. Department of Defense. Its primary purpose is a military one although it is used for many non-military purposes. As part of its military heritage, the Global Positioning System has error purposely designed into its signal. The intent of the error is to frustrate our enemy's possible uses of the system.
    Uncorrected GPS readings can be inaccurate by as much as three hundred meters. Certain procedures involving a second GPS receiver were used to correct for this error. Traditionally these corrections are made at a later time in a procedure known as post-processing. Hardware, software, and methods are now available for the corrections to be made immediately or in "real-time" mode.
    With GPS equipment that is receiving corrections in real-time, the surveyor can navigate to within a few centimeters of a predetermined coordinate point. If the coordinate point is the result of an accurate reconstruction of another surveyor's traverse, today's surveyor can be on or near an original survey monument. A search within a radius of 20 feet for a corner monument is much more likely to be productive than a search within a radius of 200 ft.
    At the time of the original GLO surveys, the government surveyor kept field notes of his measurements as his crew marked the boundaries of the unsettled land. Copies of the GLO surveyor's field notes are usually available to the present-day surveyor. Another aid to the present-day surveyor is the topographic maps produced by the United States Geological Survey. The USGS topographic quads are very accurate and usually show the section lines marked by the early surveyors. Points on these maps can be converted to latitude/longitude or other coordinate systems used in a GPS receiver. By combining known section corner coordinates, the graphic information from the USGS topographic maps, and the measurements from GLO field notes; the likely location of an original survey monument can be estimated.
    With estimated positions of original survey monuments in hand, the survey crew from TLSO will navigate to those coordinates. The survey crew will use a highly accurate GPS receiver, as well as rely on real-time corrections from a second "base" receiver to navigate to the point. The base receiver at a known point is sending, by radio signal, up-to-the-second corrections to the "rover" receiver. The calculated location is very likely in deep brush and rough terrain on the original riverbank. The survey crew will then confidently conduct a search of the immediate area for the hidden or buried corner.
    Surveyors from TLSO have achieved good results in finding original monuments with this method. In most cases the calculated corner will be within fifteen to twenty feet of the actual corner. In one instance a township corner was found that local surveyors had considered "lost" for many years. The local surveyors had considered a fence corner some distance away as the township corner and had been performing incorrect surveys for their clients.
    By using highly accurate, real-time GPS procedures, river surveys in Oklahoma are now being performed by TLSO with a greater level of confidence than was previously possible. Monuments lost for decades have been recovered using these high-tech methods. All parties, including oil companies, landowners, lease holders, and surveyors, have benefited from greater accuracy and higher quality boundary surveys.

About the Author:
Robert Keating is CEO, Topographic Engineering Company, he can be contacted at (telephone) 405-843-4847, or by E-mail: [email protected]

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