Fundamental flaws in the older vertical datum (NGVD 29) have become apparent as improved technologies have been developed. We have experienced situations where water appears to flow up hill on our monitoring equipment based on measurements using the NGVD 29 reference versus the physical reality in the field.
With the implementation of NAVD 88, we will be able to more precisely measure elevations and relative heights. The differences between the NGVD 29 and NAVD 88 values can be up to 1.5 feet, and varies from location to location across the District.
The federal government (NGS, USGS, FEMA, etc.) is moving to the new datum and will no longer support the old datum. If we delay conversion to NAVD 88, we will be financially, legally, and operationally responsible for developing and maintaining information to support the old datum.
The US Army Corp of Engineers is operating in the new datum and plans to fully convert by June 2007.
CERP and ACCELER8 currently use the new datum.
Other state and local agencies are converting, and we need to be able to trade data with them in the new datum.
Emergency Management decisions could be based on the wrong datum. Potential miscommunication of elevation data within the District or with one of our water management partners could happen at the very worst possible moment, with the greatest potential impact on human and environmental safety.
Survey benchmarks disappear at the rate of about 10% per year. The old NGVD 29 benchmarks are not being replaced, given the plans to upgrade to NAVD 88.
This map illustrates the difference in height values between NGVD 29 and NAVD 88. The difference will be higher in the south and on the east coast.
Impacts on Florida
