1. Understanding your reference datum – it can be a cost saver!
Laura Rear McLaughlin
Mapping and Charting Program Manager
Michael Michalski -- Datums Team Lead
Jerry Hovis -- Products and Services Branch Chief
NOAAs Center for Operational Oceanographic Products and Services
Dredging 2015 – Savannah, GA
October 20, 2015

2. Overview CO-OPS Introduction Tidal Datums Epoch updates
Differences between NGVD29, NAVD88 and tidal datums
VDatum
Knowing your dredging datum
Using RTK
MOA between USACE and CO-OPS

3. About the Center for Operational Oceanographic Products and Services (CO-OPS)
Mission
CO-OPS is the authoritative source for accurate, reliable, and timely tides, water levels, currents and other oceanographic information.
Our data, products and services support safe and efficient navigation, sound ecosystem stewardship, coastal hazards preparedness and response, and the understanding of climate change.
Vision
Everyone has ready access to tide, water level, current and other coastal oceanographic information needed for informed decision-making.

4. CO-OPS Observing Systems
National Water Level Observation Network (NWLON):
Water level, wind speed / direction, barometric pressure, air and water temperature, conductivity
Short-term water level station deployments
National Current Observations
Short-term current meter deployments
70 sites a year
210 NWLON Stations

5. Physical Oceanographic Real-Time System PORTS
CO-OPS Observing Systems
Physical Oceanographic Real-Time System PORTS
Measures and disseminates observations and predictions
Water levels
Currents
Salinity
Air gap
Meteorological parameters
Visibility
Waves
The Continuous Operational Real-Time Monitoring System (CORMS) is the primary system for real-time QA/QC efforts in CO-OPS.
CORMS performs thorough and robust QA/QC on all real-time data, systems, and products in the CO-OPS domain, ensuring that a reliable source of real-time data is readily available, while not disseminating data of questionable quality.
CO-OPS Data are available to the users in real-time (or near real-time) via various online graphical plots, simple text data, as well as telephone voice response.
All data and products are monitored and reviewed on a 24x7 basis, automatically and by experienced CORMS operators working on 12-hour shifts.

6. Tidal Datums
A tidal datum is a standard elevation defined by a certain phase of the tide.
Tidal datums are used as references to measure local water levels and should not be extended into differing areas.
Tidal datums are referenced to fixed points known as bench marks.
Tidal datums are the basis for establishing privately owned land, state owned land, territorial sea, exclusive economic zone, and high seas boundaries.

7. National Tidal Datum Epoch (NTDE)
Tidal Datums
National Tidal Datum Epoch (NTDE)
Official time period of tidal observations that are used for primary datum calculations
Time it takes the Earth, Moon, & Sun to complete an epoch tidal cycle
19 year time period (Present NTDE is )
Includes the longest period tidal variations (18.6 year node cycle)
Averages out seasonal fluctuations
Provides a nationally consistent tidal datum network by accounting for seasonal and apparent environmental trends in sea level that affect the accuracy of tidal datums
Considered for revision every ~20-25yrs
EPOCH

8. Tidal Datums

9. NGVD29, NAVD88, MLLW Alphabet Soup!
NGVD29 is a geodetic datum
NAVD88 is a geodetic datum
MLLW is a tidal datum
NGVD29 – National Geodetic Vertical Datum of 1929: based on calculations of mean sea level at 26 tide gauges around the U.S. and Canada and by the height of all associated bench marks.
NAVD88 – Based on holding primary tidal bench mark height fixed at Rimouski, Quebec – adjusted leveling observations to that height. Replaced NGVD29.
This Datum is Obsolete!!
This Datum is NOT mean sea level

10. NGVD29, NAVD88, MLLW Alphabet Soup!
MLLW – 19-year arithmetic mean of the lower low water observed each tidal day
We can relate MLLW to NAVD88 and NGVD29
NAVD88 can be obtained by differential leveling or static GPS observations at a tidal bench mark with geodetic elevations
Relationship to NGVD29 can be figured out with VERTCON and VDatum tools, but we don’t publish new NGVD29 elevations

11. VDatum
NOAA has a tool to convert geodetic datums into tidal datums in the coastal areas
Need to
understand
uncertainty
requirements
Vdatum.noaa.gov

12. Knowing your Dredging Datum (and Metadata)

13. Impact of using NGVD elevation instead of LMSL
Elevation for construction stakeout of London Ave. Outfall Canal floodwall construction

14. What is Impact of Ignoring a 0.23 ft Tidal Epoch Change?
Given, 10,000 ft by 400 ft channel section:
34,000 CY or $340,000 $10/CY
400 ft
10,000 ft
If this is an authorized 40-Foot Project, then you are actually maintaining it to Feet
From Dave Doyle, retired NGS

15. It’s Only 0.25’ I Can’t Dredge That Close
MLLW 60-78
-42’
But it is a bias, not a random error
From Dave Doyle, retired NGS

16. It’s Only 0.25’ I Can’t Dredge That Close
But it is a bias, not a random error
MLLW 83-01
-42’
Template based on old epoch
Template based on current epoch
From Dave Doyle, retired NGS

17. Using RTK (you still need to know tidal datum)
Ellipsoid
GPS Base station
GPS receiver
Separation Ellipsoid to MLLW
MLLW
Charted depth

18. MOA with USACE
The Hurricane Katrina Interagency Performance Evaluation Task Force (IPET) concluded that one failure point for hurricane protection structures in New Orleans was that they were not designed and constructed relative to a national vertical datum that is consistently maintained to account for changes in sea level.
The same held true for navigation projects

19. Comprehensive Evaluation of Project Datums
USACE Decision: Projects will be referenced to NOAA vertical datums EC
Guidance for a Comprehensive Evaluation of Vertical Datums on Flood Control, Shore Protection, Hurricane Protection, and Navigation Projects ER
Policies For Referencing Project Elevation Grades To Nationwide Vertical Datums

20. Comprehensive Evaluation of Project Datums
In 2013, USACE and CO-OPS designed a Memorandum of Agreement to help satisfy USACE requirement
USACE collects water levels to NOAA standards and NOAA calculates and publishes tidal datums on epoch
Datums will be updated when new datum epoch defined
Working with San Francisco, Alaska, Hawaii, New Orleans and New England Districts

21. Comprehensive Evaluation of Project Datums
PROCESS
USACE submits Work Order, Determinations and Findings (D&F) and Military Interdepartmental Purchase Request (MIPR) to CO-OPS
USACE collects WL to NOAA standards
USACE submits WL data to CO-OPS for processing and datum determination,
Tidal datums are published on NOAA website

23. Questions? Laura Rear McLaughlin Laura.Rear.McLaughlin@noaa.gov
Mike Michalski