Streamgage Streamgage Datum Datum

ConversionConversionEastern Region Height Eastern Region Height Modernization Consortium Modernization Consortium

WebinarWebinar

March 4, 2014March 4, 2014

Jim Kolva, USGS, Office of Jim Kolva, USGS, Office of Surface WaterSurface Water

Topics for DiscussionTopics for Discussion

Problem from USGS Water Problem from USGS Water perspectiveperspective

Database FactsDatabase Facts How Height Modernization might help How Height Modernization might help

the conversion effort?the conversion effort?

ProblemProblem

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

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

ProblemProblem

ProblemProblem

ProblemProblem

ProblemProblem Mixing vertical Datums creates Mixing vertical Datums creates

confusion;confusion; This mixture of Altitude Datums has This mixture of Altitude Datums has

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

In some areas of the country, the In some areas of the country, the difference between NGVD29 and difference between NGVD29 and NAVD88 can be over NAVD88 can be over 4 feet4 feet..

Partner Applications of Partner Applications of Information – NWS AHPSInformation – NWS AHPS

Partner Applications of Partner Applications of Information – NWS AHPSInformation – NWS AHPS

USGS/NWS/FEMA Flood USGS/NWS/FEMA Flood Inundation InitiativesInundation Initiatives

Policy Guidance from Policy Guidance from USGSUSGS

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

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NAVDNAVDof 1988of 1988

NGVDNGVDof 1929of 1929

SW Station Datums in the USGS NWISSW Station Datums in the USGS NWIS

>48,200 SW stations

>2,200 SW stations

Database factsDatabase facts

84,944 Surface-Water sites84,944 Surface-Water sites 62,032 determined elevation from Maps62,032 determined elevation from Maps 7,737 from Levels7,737 from Levels 8,023 unknown source8,023 unknown source 1,269 from a GPS1,269 from a GPS

4,771 already reported to 4,771 already reported to NAVD88NAVD88

Database factsDatabase facts

84,944 Surface-Water sites84,944 Surface-Water sites 62,032 determined elevation from Maps62,032 determined elevation from Maps Convert these to NAVD88 directly Convert these to NAVD88 directly

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

Database factsDatabase facts

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

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

have some analysis and conversion.have some analysis and conversion.

NGS assistance in GPS NGS assistance in GPS surveyssurveys

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

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

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

Priority stationsPriority stations

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

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

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

Funding SourcesFunding Sources

Unfunded mandate to USGS Water Unfunded mandate to USGS Water Science CentersScience Centers

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

Can the Eastern Region Height Mod Can the Eastern Region Height Mod partner with the USGS efforts?partner with the USGS efforts?

Issues to be resolvedIssues to be resolved

Accuracy of the conversion.Accuracy of the conversion. ResourcesResources

Time and manpowerTime and manpower MoneyMoney

Data already converted to Data already converted to elevation in database – Florida elevation in database – Florida effortsefforts

Questions and Questions and Comments??Comments??