Streamgage Datum Conversion Great Lakes Region Height Modernization Consortium meeting New Cumberland, PA April 13, 2011.

Streamgage Datum

ConversionGreat Lakes Region Height Modernization Consortium

meetingNew Cumberland, PA April

13, 2011

Topics for Discussion

Problem from USGS Water perspective

Database Facts How Height Modernization might help

the conversion effort?

Problem

Most USGS streamgages have a datum surveyed or estimated to NGVD29.

Streamgages established since 2002 and surveyed using a Global Positioning System (GPS) should have datum set to NAVD88.

Problem

Problem

Problem

Problem Mixing vertical Datums creates

confusion; This mixture of Altitude Datums

has created a confusing situation for streamgage information users attempting to model flood plain inundation, establish flood profiles or use other hydrologic applications.

In some areas of the country, the difference between NGVD29 and NAVD88 can be over 4 feet.

Partner Applications of Information – NWS AHPS

Partner Applications of Information – NWS AHPS

USGS/NWS/FEMA Flood Inundation Initiatives

Policy Guidance from USGS

NAVD88 is the recommended datum established in the Federal Geographic Data framework (Office of Water Information Technical memorandum 2002.01).

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NAVDof 1988

NGVDof 1929

SW Station Datums in the USGS NWIS

>48,200 SW stations

>2,200 SW stations

Database facts

84,944 Surface-Water sites 62,032 determined elevation from Maps 7,737 from Levels 8,023 unknown source 1,269 from a GPS

4,771 already reported to NAVD88

Database facts

84,944 Surface-Water sites 62,032 determined elevation from Maps Convert these to NAVD88 directly

because within existing accuracy limitations unless a determination of need for more accuracy due to data use.

Database facts

125 sites in NGS database (NGSIDB)for NAVD88 have a “gage” description. Assumed to be USGS streamgages Additional sites may be present but did

not show up in the search Approximately 17,000 sites need to

have some analysis and conversion.

NGS assistance in GPS surveys

NGS is doing updating work and GPS surveys throughout the country North Carolina and Michigan -- Will

survey in at least one reference mark at active gages in work areas

Working on best ways to easily provide reference mark descriptions and gage locations to contractors doing this work and best way to report back to USGS.

Priority stations

USGS, NGS, USACE and NWS developing priority lists of gages for conversion Pilot study in Missouri

MO has been working with Darrell Pratte, NGS Geodetic Coordinator with the Missouri DNR. Darrell has volunteered to serve in a role of oversight for field surveys and provide some personnel.

Plan was developed for conversion of gages in Missouri. Includes survey plans for those stations identified as needing that level of attention.

Priority stations

David Ulrey of USACE is working on the same effort for their streamgages. Some gages are common to both agencies so David and Paul Rydlund (USGS) will be coordinating. (Comprehensive Elevation of Project Datum – CEPD).

There is generally a lot of interest when this is discussed with other agencies and organizations. People see the need even if they don’t have the resources.

Priority stations

USGS, USACE, NOS and NWS developing priority lists of gages for conversion Pilot study in Coastal Texas

TCOON (Texas Coastal Ocean Observation Network) and Texas A&M--Corpus Christi

Seeking funding to upgrade USGS sites to meet NOS tidal gage standards, both NAVD88 and local tidal datum.

Next “beta” areas are the North Atlantic coast and the Great Lakes

Funding Sources

Unfunded mandate to USGS Water Science Centers

Some will need GPS surveys to meet required accuracies or because of instability issues.

Can the Great Lakes Height Mod partner with the USGS efforts?

Issues to be resolved

Accuracy of the conversion. Resources

Time and manpower Money

Data already converted to elevation in database – Florida efforts

Questions and Comments??