Public Information Statement
Issued by NWS Sterling, VA

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000 NOUS41 KLWX 011614 PNSLWX DCZ001-VAZ054-012000- PUBLIC INFORMATION STATEMENT NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1214 PM EDT WED APR 1 2015 ...ELEVATION ADJUSTMENT FOR WASHINGTON MEAN LOW WATER BEGINS MONDAY APRIL 6TH... ON MONDAY APRIL 6TH...THE BASE ELEVATION OF WASHINGTON MEAN LOW WATER /WMLW/ WILL BE SLIGHTLY ADJUSTED...AFFECTING THE POTOMAC RIVER AT WISCONSIN AVENUE/GEORGETOWN...SITE ID GTND2. THIS GAUGE REPORTS THE WATER HEIGHT ABOVE WASHINGTON MEAN LOW WATER...AND WILL CONTINUE TO DO SO. AS PART OF A STUDY CONDUCTED BY THE US ARMY CORPS OF ENGINEERS... THE ELEVATIONS OF BENCHMARKS FROM THE NATIONAL GEODETIC SURVEY LISTED IN THE NORTH AMERICAN VERTICAL DATUM OF 1988 /NAVD88/ WERE COMPARED TO THE ELEVATIONS OF THOSE SAME BENCHMARKS ABOVE WASHINGTON MEAN LOW WATER AS DENOTED IN THE CORPS POTOMAC PARK MANUAL. IT HAS BEEN DETERMINED THROUGH THIS STUDY THAT THE DIFFERENCE BETWEEN NAVD88 AND WMLW IS 2.26 FEET. THIS COMPARISON IS DEEMED MORE ACCURATE BECAUSE THE PREVIOUS DIFFERENCE OF 2.18 FEET WAS BASED ON A COMPUTER-BASED CONVERSION FROM YET ANOTHER DATUM...THE NATIONAL GEODETIC VERTICAL DATUM OF 1929 /NGVD29/. THE DIFFERENCE IS SO SMALL /ABOUT ONE INCH/ THAT IT HAS NO IMPACT ON FLOOD STAGE OR FLOOD CATEGORIES AT THE SITE. DATA WILL CONTINUE TO BE REPORTED AS HEIGHT ABOVE WASHINGTON MEAN LOW WATER JUST AS IT HAS BEEN. THIS MESSAGE IS SIMPLY TO NOTIFY USERS WHO REFERENCE NAVD88 THAT THE CONVERSION TO THAT ELEVATION WILL CHANGE. USERS WHO HAVE ANY QUESTIONS SHOULD EMAIL SENIOR SERVICE HYDROLOGIST JASON ELLIOTT AT: JASON.ELLIOTT@NOAA.GOV $$

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