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

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

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.

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

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.

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) 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 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, 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

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

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)

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

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 400 ft 10,000 ft If this is an authorized 40-Foot Project, then you are actually maintaining it to 40.23 Feet From Dave Doyle, retired NGS

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

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

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

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

Comprehensive Evaluation of Project Datums 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

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

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