An important issue 

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Posts: 6

Joined: 11/13/2008
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Locally, we had substantial damage from hurricane Ike, which has brought to light an unfortunate comedy of errors:

A surveying company, and surveyors are looking at professional and civil problems due to using a USGS monument that has been determined is around 3' lower than was recorded years ago. Otherwise, existing homes are unable to be insured due to the elevation above sea level. Some home would have avoided flooding if the property owners had built to the higher elevation the survey indicated. The surveyors certified the elevations, but used the benchmark that supposedly was placed in soil that subsided 3 feet. The property owner have a legal leg to stand on, but unfortunately all of their efforts for compensation may only end in judgements, if anything. The professional reputations, and licensing of the surveying companies is up in the air until a final determination.
  Monday, February 16, 2009 at 5:07:31 PM
Posts: 42
Location: Gonzales, La USA

Joined: 10/20/2008
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This is not a new problem.  FEMA policy in areas of rapid or significant subsidence has been to rely on the most recent published values for vertical marks.  It is not suffcient to file a value for a benchmark and then rely upon that value years later.  NGS marks or CORPS values must be retrieved at the date that the work is performed.  Coastal areas of the Gulf of Mexico are experiencing significant movement.  Changes in the vertical datum have also been occuring.  FEMA maps, regulations and policies do not accomodate vertical changes very well at all.  I have been battling FEMA, NGS and others over the issue of vertical movement since 1975.  The only answer seems to be frequent updating of vertical data and frequent revisions of flood hazard area mapping.
  Tuesday, February 17, 2009 at 9:53:41 AM
Deward Bowles
Posts: 33
Location: Houston, Harris

Joined: 3/29/2009
Reply  Re: An important issue Flag »  Reply »
It is important to read the Flood Study for the County or Parish you are performing the certificate in.

My understanding is that the original Benchmark was obliterated in this case. The City was in possession of some reference data from this Benchmark produced some years earlier by another Land Surveyor. The surveyors in question obtained this reference data from the City and then used it to produce the certificates. The original Benchmark was still published on the NGS sheets with old datum and observation values and this is what the reference data was based on. However the current FIRM for that particular area listed the same benchmark some 3' lower than the NGS value indicating the subsidence. Indeed there were studies performed during the period the most recent FIRM for this area was produced showing the benchmark in question had subsided some 3' and there seems little doubt that this study was the reason for the elevation adjustment on the Benchmark in question shown on the FIRM. There is no way to observe the original Benchmark. I understand that observations using current datum have been made on refrence data provided by the City to the surveyors who produced these certificates. The observations indicate as much as 3' of difference.

I have a lot of sympathy for these Land Surveyors but at the same time there seems there were plenty of oppurtunities for them to see red flags....if they would have been looking.
  Saturday, February 20, 2010 at 11:28:29 AM

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