Potomac River at Williamsport, Washington County MD (WLLM2)
Gage Location: Washington County, Maryland	Site Location: Washington County, Maryland
Latitude: 39.609	Longitude: -77.848	Elevation: 327.7 ft. MSL	Drainage Area: 4943 Sq. Mi.
Minor Stage: 23 ft.	Moderate Stage: 25 ft.	Major Stage: 28 ft.
First Flood: 1936-03-18	Last Flood: 1996-09-08 Crest: 31.1 ft.	Datum change: 1932-01-01	Number of Floods: 8

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Height Above Flood Stage for Entire Period of Record Height Above FS Total Occurence Percent of Crest Occurrence Cumulative Total Flood Occurrence Percent of Floods above Listed Value 25 ft to 26 ft 1 12.5 25 ft or above 8 100.0 26 ft to 27 ft 0 0.0 26 ft or above 7 87.5 27 ft to 28 ft 0 0.0 27 ft or above 7 87.5 28 ft to 29 ft 0 0.0 28 ft or above 7 87.5 29 ft to 30 ft 0 0.0 29 ft or above 7 87.5 30 ft to 31 ft 0 0.0 30 ft or above 7 87.5 31 ft to 32 ft 1 12.5 31 ft or above 7 87.5 32 ft to 33 ft 0 0.0 32 ft or above 6 75.0 33 ft to 34 ft 0 0.0 33 ft or above 6 75.0 34 ft to 35 ft 2 25.0 34 ft or above 6 75.0 35 ft to 36 ft 0 0.0 35 ft or above 4 50.0 36 ft to 37 ft 2 25.0 36 ft or above 4 50.0 37 ft to 38 ft 1 12.5 37 ft or above 2 25.0 38 ft to 39 ft 0 0.0 38 ft or above 1 12.5 39 ft to 40 ft 0 0.0 39 ft or above 1 12.5 40 ft to 41 ft 0 0.0 40 ft or above 1 12.5 41 ft to 42 ft 0 0.0 41 ft or above 1 12.5 42 ft to 43 ft 0 0.0 42 ft or above 1 12.5 43 ft to 44 ft 0 0.0 43 ft or above 1 12.5 44 ft to 45 ft 0 0.0 44 ft or above 1 12.5 45 ft to 46 ft 0 0.0 45 ft or above 1 12.5 46 ft to 47 ft 0 0.0 46 ft or above 1 12.5 47 ft to 48 ft 0 0.0 47 ft or above 1 12.5 48 ft to 49 ft 1 12.5 48 ft or above 1 12.5

Height Above Flood Stage After Datum Change Height Above FS Total Occurence Percent of Crest Occurrence Cumulative Total Flood Occurrence Percent of Floods above Listed Value 23 ft to 24 ft 0 0.0 23 ft or above 8 100.0 24 ft to 25 ft 0 0.0 24 ft or above 8 100.0 25 ft to 26 ft 1 12.5 25 ft or above 8 100.0 26 ft to 27 ft 0 0.0 26 ft or above 7 87.5 27 ft to 28 ft 0 0.0 27 ft or above 7 87.5 28 ft to 29 ft 0 0.0 28 ft or above 7 87.5 29 ft to 30 ft 0 0.0 29 ft or above 7 87.5 30 ft to 31 ft 0 0.0 30 ft or above 7 87.5 31 ft to 32 ft 1 12.5 31 ft or above 7 87.5 32 ft to 33 ft 0 0.0 32 ft or above 6 75.0 33 ft to 34 ft 0 0.0 33 ft or above 6 75.0 34 ft to 35 ft 2 25.0 34 ft or above 6 75.0 35 ft to 36 ft 0 0.0 35 ft or above 4 50.0 36 ft to 37 ft 2 25.0 36 ft or above 4 50.0 37 ft to 38 ft 1 12.5 37 ft or above 2 25.0 38 ft to 39 ft 0 0.0 38 ft or above 1 12.5 39 ft to 40 ft 0 0.0 39 ft or above 1 12.5 40 ft to 41 ft 0 0.0 40 ft or above 1 12.5 41 ft to 42 ft 0 0.0 41 ft or above 1 12.5 42 ft to 43 ft 0 0.0 42 ft or above 1 12.5 43 ft to 44 ft 0 0.0 43 ft or above 1 12.5 44 ft to 45 ft 0 0.0 44 ft or above 1 12.5 45 ft to 46 ft 0 0.0 45 ft or above 1 12.5 46 ft to 47 ft 0 0.0 46 ft or above 1 12.5 47 ft to 48 ft 0 0.0 47 ft or above 1 12.5 48 ft to 49 ft 1 12.5 48 ft or above 1 12.5

Codes and description

C1|Crest information looks unreliable and incomplete and not used in frequency calculations. Some of the floods are based on current flood stage and nearby gage information.
C2|Crest information looks reliable despite potential problems. This data was used in frequency calculations.
C3|Crest height estimated by the USGS.
C4|Crest height is from the National Weather Service.
C5|Crest height affected by backwater.
C6|Crest occurred at a previous flood stage that is lower than the current flood stage. The crests below the new flood stage are not used in flood frequency calculations.
C7|Crest from USGS yearly peak and/or date is different than the crest we provide. In many cases MARFC uses crest based on backwater or ice effects.
C8|Crest month or day of occurrence has been estimated by The Middle Atlantic River Forecast Center usually based on nearby gage information.
C9|Crest date (day) in the month is unknown.
F1|Flow is an estimate.
F2|Flow affected by regulation or diversion and in some cases to an unknown degree.
F3|Flow effected by snow-melt, ice jam or debris jam break up.
F4|Flow affected by dam failure.
F5|Flow - All or part of the record affected by urbanization, mining, agricultural changes, channelization or other factors.
G1|Gage height at a different site and/or datum.
G2|Gage is not an official USGS gage with crests provided by the NWS. Crest information looks unreliable and incomplete and not used in flood frequency calculations.
G3|Gage datum changed during this year.
none,No code; Good Data

Updated: 08:09 AM Feb 08, 2013