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CENTER for OPERATIONAL OCEANOGRAPHIC PRODUCTS and SERVICES

International Great Lakes Datum (IGLD) Overview

Coastal Zone 2011“Cool Geodetic Resources For Your

Project”A National Ocean Service, NOAA

Presentation”

Stephen Gill, Chief ScientistNOAA/NOS Center for

Operational Oceanographic Products and Services


An International Partnership

Natural ResourcesCanada

EnvironmentCanada

Fisheries and Oceans Canada


Why and How was IGLD Established?

•The management of Great Lake water resources is a shared responsibility between the US and Canada under the auspices of the International Joint Commission and other coordinating bodies.

•An international study was first established in 1953 jointly by Canada and the US in recognition of the need for agreement on hydrologic and hydraulic factors and acceptance of common reference datum.

•The Vertical Control-Waters Levels Subcommittee of the Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data established the International Great Lakes Datum (1955) that was implemented in January 1962 and used for the following 30-years.


Why and How was IGLD Established?

•The Vertical Control-Water Levels Subcommittee addressed the following topics in the course of establishment of IGLD (1955):

• Establishment of a datum reference zero near the mouth of the St Lawence River.

•First-order leveling from the reference zero to Lake Ontario and between the lakes.

•Crustal movement in the Great Lakes Area, and

•Establishment of elevations of bench marks and reference surfaces in the Great lakes-St. Lawrence River System.


Why and How was IGLD(1985) Established?

•The Vertical Control-Water Levels Subcommittee noted that crustal movements causesbench marks to shift in position, typically only small changes over a 3-5 –year period , but significant after 25-30 years.

• The development of IGLD (1985) was designed to coincide with the development of the North American Vertical Datum (1988).

• The US-Canadian Network adjustment adopted for IGLD (1985) was based on 78 geodetic leveling loops and connecting over 80 water level gauges.

• Based on the recommendations of the Coordinating Committee, IGLD (1985) was adopted and implemented in January 1992


Features of IGLD(1985)

• Elevations, consistent with one another as of a recent update (1985) were provided for bench marks throughout the Great Lakes-St. Lawrence River System, with the reference zero at Pointe-au-Pere/ Rimouski.

• The elevations given on IGLD (1985) are based on the dynamic principle, and are therefore more suitable for hydraulic studies.

• Elevations on IGLD (1985) greatly facilitated hydraulic, hydrographic and other engineering studies.


IGLD 85 Heights

•Dynamic heights are relevant near large bodies of water such as reservoirs or very large lakes, so the Great Lakes are an ideal candidate for dynamic heights. The Great Lakes are referenced to the International Great Lakes Datum of 1985 (IGLD 85) dynamic heights.

• IGLD (1985) elevations and NAVD (1988) elevations are not the same because IGLD (1985) elevations are published as dynamic heights and NAVD (1988) elevations are published as Helmert orthometric heights.


Hydraulic Correctors

•An important component of the IGLD (1985) system is the computation of Hydraulic Correctors (HC).

• Hydraulic correctors are applied to each gauge location on a lake assuming each location should have the same Mean Water Level (MWL) as the Master Station for each lake.

• This is accomplished by performing simultaneous comparisons of MWL between subordinate gauges and the Master Stations for the summer months (June- September) over a 7-year period. For IGLD (1985)this was from 1982-1988. The comparisons were referenced to Dynamic Heights at each station to obtain the hydraulic corrector.

• The Hydraulic Corrector for each gauge was then subtracted from the Dynamic Water Surface elevation at the station to obtain IGLD (1985) at the subordinate gauge.


Master Stations for Each Great Lake

• Lake Ontario - Oswego, NY• Lake Erie - Fairport, Ohio• Lake St. Clair - St. Clair Shores, Michigan• Lake Huron - Harbor Beach, Michigan• Lake Michigan - Harbor Beach, Michigan• Lake Superior - Marquette, Michigan


Why is the IGLD important?

• Coordinated management of worlds largest fresh water resources, supports regulatory decisions.

•A fundamental requirement for shared management is a common elevation reference datum for water levels.

• IGLD is the reference for nautical chart datum/low water datum; update nautical charts for navigation safety.

• Accurate reference system provides geophysical framework for marine spatial planning.

• Supports beach re-nourishment and marsh/wetlands restoration.

• Climate change monitoring and assessment.


Navigation Datums for each Great Lake and Interconnecting Waterways are Defined Relative to IGLD – These Reference Datums are called

Low Water Datum (LWD)

Elevations in Meters


Updating the International Great Lakes Datum (IGLD)

Movement of the earth’s crust due to isostatic rebound requires the revision of the datum, or elevation reference system used to define water levels within the Great Lakes-St. Lawrence River system, every 25 to 30 years. This system, one of the world’s greatest fresh water resources, is

shared and its resources jointly managed by the United States and Canada. The revision of this elevation reference system, the

International Great Lakes Datum (IGLD) requires the updating of the Dynamic Heights so as to reference IGLD at approximately 140 small harbors, 50 subordinate control stations, as compared to the 5 master

control stations in the United States alone. The revision is targeted for the central year 2015, implementation several years later. The revised

datum is critical for updating nautical charts for navigation safety, particularly during periods of low water levels.


Why is a new IGLD Update Required?

Isostatic rebound continues from the retreat of the glaciers results in movement of the earth’s crust.


Milwaukee

Thessalon

Parry Sound

Cleveland

Harbor Beach

Why is an IGLD Update Required?

• The rate is not uniform, with northern/western Lakes generally tilting up while southern/eastern Lakes are subsiding.

• Systematic inaccuracies inherent to 1980’s survey technology increased as level lines run from east to western Lakes.

• Differences ranged from inches to almost a foot and a half from east to west in the last update from IGLD55 to IGLD85.


How will IGLD1985 be updated to IGLD2015?

Two coordinated components:

• Height modernization – Geoid based vertical datum

• Seasonal water level gauging – update heights and low water datum for small harbors


Height Modernization

• Accurate gravity is foundation of heights.

• National Geodetic Survey recently published GRAV-D plan for modernization of new national vertical datum for 2018.

• Enables accurate transformation of ellipsoid (GPS) to orthometric (geodetic) heights.

• Improves accuracy of heights to a few centimeters

• Enables use of GPS for IGLD, eliminates need for more costly line-of-sight geodetic surveying

The GRAV-D Project:Gravity for the Redefinitionof the American Vertical Datum


Continuously Operating Continuously Operating Reference Stations (CORS)Reference Stations (CORS)

13 CORS co-located 13 CORS co-located with NWLON stationswith NWLON stations

Monitor varying rates Monitor varying rates of isostatic reboundof isostatic rebound

Helps to identify Helps to identify absolute long-term absolute long-term water level changeswater level changes

Navigational Navigational positioningpositioning


CORS Operating at Great Lakes Gauging Stations in Support of IGLD Update

Lake OntarioOswego – (OSPA)

Lake ErieBuffalo – (BFNY)

Cleveland – (OHCD)Marblehead – (OHMH)

Lake HuronHarbor Beach – (HBCH)

Alpena – (MIAL)Lake Michigan

Ludington – (MILT)Calumet Harbor – (CALU)

St Mary’s RiverWest Neebish Island – (MINB)

Lake SuperiorPt. Iroquois – (PTIR)Marquette – (MIMQ)

Grand Marais – (GDMA)Two gauging stations built in 08 are ready for CORS equipment to be installed, Mackinaw

City and Little Rapids, MI.Two new gauging stations are being built summer of 09 with expectations for installing

CORS equipment, Holland and Menominee, MI.


Seasonal Water LevelGauging Program

Update low water datum at >125 sites in small harbors and rivers

Requires data collection, localized leveling, and GPS observations at each site

Determination of hydraulic corrector for each site is the key product from the effort

Funding levels included in the CO-OPS strategic plan for the IGLD update

Support from various partners such as MDOT, WIDOT, MNDOT, OHDOT and other agencies is essential


NOAA Seasonal Gauging ProgramIGLD 2015 Update

Install 20-25 sites eachsummer; operate June – September5-6 years data collection


Preliminary Planning for IGLD Update

Planning team of NGS and CO-OPS personnel formed in April 2008

Planning first presented at the Canadian Hydrographic Conference in May 2008

Joint strategic planning between NGS and CO-OPS being emphasized

FY11 budget request submitted in May 2008 – included GRAV-D and seasonal water level gauging projects needed to update IGLD – but was not funded


Preliminary Scaled-Back Planning for IGLD Update

Compute new updated Mean Water Level at 5 Master stations over new time period.

Continue to obtain GPS measurements at water level stations

Update IGLD elevations only at existing Great lakes stations and not at the >125 historical season gauging locations.

Continue with height modernization and GRAV-D in the region.

Continue to pursue local and federal funding opportunities to complete full implementation


Outreach

Increased awareness of the need for the IGLD update increases chances of funding .

CHC Poster Session (May 08) in Victoria, BC. NGS Height Modernization meetings (Sept 08) in

Wisconsin and March 09 in Michigan CO-OPS and NGS seeking additional outreach

opportunities and partners Similar actions by Canada demonstrate the

international partnership required for the project IJC and CCGLBHHD support also needed


CO-OPS and NGS Contacts

Jeff Oyler, Field Operations Division

[email protected]

757-842-4431

Dr. Dru Smith, Chief Geodesist, NGS

[email protected]

301-713-3222 x 144

Tom Landon, Engineering Division

[email protected]

301-713-2897 x191

http://tidesandcurrents.noaa.gov/

http://geodesy.noaa.gov/


Upcoming Training and Informational Opportunities

Webinar:Introduction to Geodetic and Tidal Vertical Datums <http://www.ngs.noaa.gov/corbin/class_description/Geodetic_Tidal_Datums_0811.shtml>, August 16th and 18th, 2011 Introduction to Geodetic Vertical Datums/: Tuesday, August 16, 2011, 1:00-

4:00pm ET, presenter Dave Minkel. Introduction to Tidal Datums/: Thursday, August 18, 2011, 1:00-4:00pm ET,

presenters Michael Michalski and Scott Duncan.

Geodetic Digital Leveling Class <http://www.ngs.noaa.gov/corbin/class_description/leveling_1011.shtml>, October 25-27, 2011. Open seats. On-site class, to be held at the Corbin Training Center.

Sign-up and get more information at:

http://www.ngs.noaa.gov/corbin/calendar.shtml

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