Streamgage Datum Conversion Eastern Region Height Modernization Consortium Webinar March 4, 2014 Jim Kolva, USGS, Office of Surface Water

Topics for Discussion Problem from USGS Water perspective Problem from USGS Water perspective Database Facts Database Facts How Height Modernization might help the conversion effort? How Height Modernization might help the conversion effort?

Problem Most USGS streamgages have a datum surveyed or estimated to NGVD29. 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. 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; 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. 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. In some areas of the country, the difference between NGVD29 and NAVD88 can be over 4 feet.

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 ).

NAVD of 1988 NGVD of 1929 SW Station Datums in the USGS NWIS >48,200 SW stations >2,200 SW stations

Database facts 84,944 Surface-Water sites 84,944 Surface-Water sites 62,032 determined elevation from Maps 62,032 determined elevation from Maps 7,737 from Levels 7,737 from Levels 8,023 unknown source 8,023 unknown source 1,269 from a GPS 1,269 from a GPS 4,771 already reported to NAVD88 4,771 already reported to NAVD88

Database facts 84,944 Surface-Water sites 84,944 Surface-Water sites 62,032 determined elevation from Maps 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. 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. 125 sites in NGS database (NGSIDB)for NAVD88 have a “gage” description. Assumed to be USGS streamgages Assumed to be USGS streamgages Additional sites may be present but did not show up in the search Additional sites may be present but did not show up in the search Approximately 17,000 sites need to have some analysis and conversion. 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 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 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. 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 USGS, NGS, USACE and NWS developing priority lists of gages for conversion Pilot study in Missouri 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. 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. Plan was developed for conversion of gages in Missouri. Includes survey plans for those stations identified as needing that level of attention.

Funding Sources Unfunded mandate to USGS Water Science Centers Unfunded mandate to USGS Water Science Centers Some will need GPS surveys to meet required accuracies or because of instability issues. Some will need GPS surveys to meet required accuracies or because of instability issues. Can the Eastern Region Height Mod partner with the USGS efforts? Can the Eastern Region Height Mod partner with the USGS efforts?

Issues to be resolved Accuracy of the conversion. Accuracy of the conversion. Resources Resources Time and manpower Time and manpower Money Money Data already converted to elevation in database – Florida efforts Data already converted to elevation in database – Florida efforts

Questions and Comments??