Understanding your reference datum – it can be a cost saver!

NOAA’s CENTER for OPERATIONAL OCEANOGRAPHIC PRODUCTS and SERVICESNOAA’s CENTER for OPERATIONAL OCEANOGRAPHIC PRODUCTS and SERVICES

Understanding your reference datum – it can be a cost saver!

Laura Rear McLaughlin Mapping and Charting Program Manager

Michael Michalski -- Datums Team LeadJerry Hovis -- Products and Services Branch Chief

NOAAs Center for Operational Oceanographic Products and ServicesDredging 2015 – Savannah, GA

October 20, 2015


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


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.

About the Center for Operational Oceanographic Products and Services (CO-OPS)

VisionVisionEveryone has ready Everyone has ready access to tide, water level, access to tide, water level, current and other coastal current and other coastal oceanographic information oceanographic information needed for informed needed for informed decision-making. decision-making.


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


Measures and disseminates observations and predictions

Water levels Currents Salinity Air gap Meteorological parameters Visibility Waves

CO-OPS Observing Systems

Physical Oceanographic Real-Time SystemPORTS


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.


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 1983-2001)– 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

1983-2001 EPOCH


Tidal Datums


NGVD29, NAVD88, MLLWAlphabet 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


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

NGVD29, NAVD88, MLLWAlphabet Soup!


VDatum NOAA has a tool to convert geodetic datums

into tidal datums in the coastal areas

Need to understand uncertainty requirements

Vdatum.noaa.gov


Knowing your Dredging Datum (and Metadata)


Elevation for construction stakeout of London Ave. Outfall Canal floodwall construction

Impact of using NGVD elevation instead of LMSL


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 Overdredging @ $10/CY

If this is an authorized 40-Foot Project, then you are actually maintaining it to 40.23 Feet

400 ft

10,000 ft

From Dave Doyle, retired NGS


But it is a bias, not a random error

-42’


It’s Only 0.25’I Can’t Dredge That Close


But it is a bias, not a random error

-42’

Template based on old epochTemplate based on current epoch


It’s Only 0.25’I Can’t Dredge That Close


Using RTK (you still need to know tidal datum)

Ellipsoid

MLLW

Charted depth

GPS Base station

GPS receiverSeparation Ellipsoid to MLLW


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


USACE Decision: Projects will be referenced to NOAA vertical datums EC - 1110-2-6065

Guidance for a Comprehensive Evaluation of Vertical Datums on Flood Control, Shore Protection, Hurricane Protection, and Navigation Projects

ER - 1110-2-8160 Policies For Referencing Project Elevation Grades

To Nationwide Vertical Datums

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 83-01 epoch

• Datums will be updated when new datum epoch defined

• Working with San Francisco, Alaska, Hawaii, New Orleans and New England Districts



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




Questions? Laura Rear McLaughlin [email protected]

Mike Michalski [email protected]

mailto:[email protected]

mailto:[email protected]

Documents

Understanding your reference datum – it can be a cost saver!