Haven projects sunk up to 2 feet giving protection heights of say 10 ft instead of 12 ft?
Yes, some projects have elevation values that are 2 lower. That does not mean that they sank 2. We must make it clear that one can not simply subtract todays NAVD88(2004.65) elevation from an NGVD29(64) elevation to get the amount of subsidence. Please see the explanation below. The change in Datum is a change in where we measure from to establish elevations on structures, benchmarks, etc. The datum shift from NGVD29 to NAVD88 is not constant. The datum surfaces are not parallel and therefore vary with the location. A datum change does not change the relationship of the levee heights to the water. Please see the explanation below. The difference in the apparent elevations at our hurricane protection projects is a product of several factors. 1. Datum Shift: The zero reference (or where the ruler starts) was changed from NGVD29 to NAVD88. This has nothing to do with the physical elevation with respect to sea level. This is only a change in where the elevation is measured from. It’s like
See above… Yes, some projects have elevation values that are 2 lower. That does not mean that they sank 2. We must make it clear that one can not simply subtract todays NAVD88(2004.65) elevation from an NGVD29(64) elevation to get the amount of subsidence. Please see the explanation below. The change in Datum is a change in where we measure from to establish elevations on structures, benchmarks, etc. The datum shift from NGVD29 to NAVD88 is not constant. The datum surfaces are not parallel and therefore vary with the location. A datum change does not change the relationship of the levee heights to the water. Please see the explanation below. The difference in the apparent elevations at our hurricane protection projects is a product of several factors. 1. Datum Shift: The zero reference (or where the ruler starts) was changed from NGVD29 to NAVD88. This has nothing to do with the physical elevation with respect to sea level. This is only a change in where the elevation is measured fro
