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Patuxent River near Unity

Highest listed crest 18.60 ftFlood stage 8.0 ft41 crests since 1945

The Patuxent River near Unity crested at major flood stage 1 time among the 41 crests the National Weather Service lists from 1945 to 2021. The highest, 18.60 ft on September 11, 1971, was major flooding, 10.60 feet above flood stage. 1 other gauge on the Patuxent River crested above flood stage within a week of it.

The gauge

Highest listed crest
18.60 ft
September 11, 1971; 21,800 cubic feet per second
Flood stage
8.0 ft
Major flooding from 18.0 ft
Crests at major
1
32nd of 108 gauges in Maryland
Most recent flood crest
September 23, 2021
8.54 ft, minor flooding
Location
Montgomery County
Near Gaithersburg (9.7 mi), Rockville (11.9 mi), Laurel (14.4 mi)

Flood stages

The thresholds the National Weather Service uses for this gauge today, and how many listed crests reached each.

Flood categories, Patuxent River near Unity
Action stage7.09Jul 9, 2012The level at which the NWS or its partners begin to take action
Flood stage (minor)8.026Sep 23, 2021Minimal or no property damage, but possibly some public threat
Moderate flood stage11.05Oct 1, 1979Some inundation of structures and roads near the stream
Major flood stage18.01Sep 11, 1971Extensive inundation of structures and roads

Every listed crest

41 crests from 1945 to 2021. Filled: at or above flood stage. Hover a crest for its date and stage.

Listed crests at the Patuxent River near Unity, 1945 to 2021 5101520ft Flood stage 8.0 ftMajor 18.0 ft Aug 1, 1945: 13.58 ft, moderate flooding; 8,060 cubic feet per secondJun 2, 1946: 8.02 ft, minor flooding; 1,920 cubic feet per secondSep 1, 1952: 8.95 ft, minor flooding; 3,490 cubic feet per secondNov 22, 1952: 8.09 ft, minor flooding; 2,220 cubic feet per secondAug 13, 1955: 8.06 ft, minor flooding; 2,200 cubic feet per secondJul 21, 1956: 14.35 ft, moderate flooding; 10,700 cubic feet per secondDec 20, 1957: 8.17 ft, minor flooding; 2,290 cubic feet per secondSep 14, 1966: 8.90 ft, minor flooding; 2,920 cubic feet per secondAug 27, 1967: 7.52 ft, action stage; 1,800 cubic feet per secondSep 10, 1968: 7.01 ft, action stage; 1,490 cubic feet per secondJul 26, 1969: 7.18 ft, action stage; 1,590 cubic feet per secondSep 11, 1971: 18.60 ft, major flooding; 21,800 cubic feet per secondJun 22, 1972: 16.10 ft, moderate flooding; 14,500 cubic feet per secondSep 26, 1975: 12.69 ft, moderate flooding; 7,680 cubic feet per secondJan 1, 1976: 7.82 ft, action stage; 2,040 cubic feet per secondJan 26, 1978: 8.75 ft, minor flooding; 2,790 cubic feet per secondSep 6, 1979: 9.15 ft, minor flooding; 3,150 cubic feet per secondOct 1, 1979: 11.72 ft, moderate flooding; 6,190 cubic feet per secondJun 21, 1983: 7.76 ft, action stage; 2,010 cubic feet per secondFeb 12, 1985: 8.24 ft, minor flooding; 2,370 cubic feet per secondMay 24, 1988: 7.08 ft, action stage; 1,550 cubic feet per secondMay 6, 1989: 10.54 ft, minor flooding; 4,640 cubic feet per secondOct 23, 1990: 8.82 ft, minor flooding; 2,850 cubic feet per secondNov 28, 1993: 8.97 ft, minor flooding; 2,980 cubic feet per secondSep 6, 1996: 10.52 ft, minor flooding; 4,610 cubic feet per secondMar 21, 1998: 7.60 ft, action stage; 1,890 cubic feet per secondJun 13, 2003: 9.81 ft, minor flooding; 3,900 cubic feet per secondDec 11, 2003: 10.02 ft, minor flooding; 4,120 cubic feet per secondJun 10, 2005: 7.25 ft, action stage; 1,760 cubic feet per secondJun 27, 2006: 10.36 ft, minor flooding; 4,330 cubic feet per secondNov 16, 2006: 10.31 ft, minor flooding; 4,420 cubic feet per secondJul 9, 2012: 7.18 ft, action stage; 1,710 cubic feet per secondJan 31, 2013: 10.49 ft, minor flooding; 4,620 cubic feet per secondApr 30, 2014: 8.81 ft, minor flooding; 2,970 cubic feet per secondMay 16, 2014: 8.60 ft, minor flooding; 2,794 cubic feet per secondJun 28, 2015: 8.76 ft, minor flooding; 2,928 cubic feet per secondJul 31, 2016: 9.83 ft, minor flooding; 3,755 cubic feet per secondJul 22, 2018: 8.60 ft, minor flooding; 2,510 cubic feet per secondJul 8, 2019: 8.01 ft, minor flooding; 2,084 cubic feet per secondNov 1, 2019: 9.15 ft, minor flooding; 3,014 cubic feet per secondSep 23, 2021: 8.54 ft, minor flooding; 2,290 cubic feet per second Highest, 18.60 ft, Sep 11, 1971 19501960197019801990200020102020

Crests at or above flood stage, by decade

Crests at or above flood stage per decade, Patuxent River near Unity 1940s: 2 1950s: 5 1960s: 1 1970s: 6 1980s: 2 1990s: 3 2000s: 4 2010s: 8 8 2020s: 1 1940s1950s1960s1970s1980s1990s2000s2010s2020s
  1. These are the crests the local National Weather Service office lists for the gauge: the highest on record and recent crests. Lesser floods between them may be missing, so counts by decade are a floor.
  2. Categories use today's flood stages. Levees, dams and channel changes since a crest can make old and new stages not directly comparable.

Highest crests

Highest listed crests, Patuxent River near Unity
1Sep 11, 197118.60+10.60Major21,800
2Jun 22, 197216.10+8.10Moderate14,500
3Jul 21, 195614.35+6.35Moderate10,700
4Aug 1, 194513.58+5.58Moderate8,060
5Sep 26, 197512.69+4.69Moderate7,680
6Oct 1, 197911.72+3.72Moderate6,190
7May 6, 198910.54+2.54Minor4,640
8Sep 6, 199610.52+2.52Minor4,610
9Jan 31, 201310.49+2.49Minor4,620
10Jun 27, 200610.36+2.36Minor4,330
11Nov 16, 200610.31+2.31Minor4,420
12Dec 11, 200310.02+2.02Minor4,120
13Jul 31, 20169.83+1.83Minor3,755
14Jun 13, 20039.81+1.81Minor3,900
15Sep 6, 19799.15+1.15Minor3,150
16Nov 1, 20199.15+1.15Minor3,014
17Nov 28, 19938.97+0.97Minor2,980
18Sep 1, 19528.95+0.95Minor3,490
19Sep 14, 19668.90+0.90Minor2,920
20Oct 23, 19908.82+0.82Minor2,850
21Apr 30, 20148.81+0.81Minor2,970
22Jun 28, 20158.76+0.76Minor2,928
23Jan 26, 19788.75+0.75Minor2,790
24May 16, 20148.60+0.60Minor2,794
25Jul 22, 20188.60+0.60Minor2,510
26Sep 23, 20218.54+0.54Minor2,290
27Feb 12, 19858.24+0.24Minor2,370
28Dec 20, 19578.17+0.17Minor2,290
29Nov 22, 19528.09+0.09Minor2,220
30Aug 13, 19558.06+0.06Minor2,200
31Jun 2, 19468.02+0.02Minor1,920
32Jul 8, 20198.01+0.01Minor2,084
33Jan 1, 19767.82−0.18Action2,040
34Jun 21, 19837.76−0.24Action2,010
35Mar 21, 19987.60−0.40Action1,890
36Aug 27, 19677.52−0.48Action1,800
37Jun 10, 20057.25−0.75Action1,760
38Jul 26, 19697.18−0.82Action1,590
39Jul 9, 20127.18−0.82Action1,710
40May 24, 19887.08−0.92Action1,550
41Sep 10, 19687.01−0.99Action1,490

The worst floods along the Patuxent River

For this gauge's highest crests, the other gauges on the Patuxent River that crested above flood stage within a week.

September 11, 1971: 18.60 ft here, major flooding

June 22, 1972: 16.10 ft here, moderate flooding

July 21, 1956: 14.35 ft here, moderate flooding

Gauges on the Patuxent River

Flood gauges sharing the river's name, linked within 80 miles of one another.

Flood gauges on the Patuxent River
Solomons Island (IN MLLW)MD3.04.82 ft, Oct 29, 20210
Brighton DamMD9.011.88 ft, Jan 31, 20130
Duckett Dam near LaurelMD9.525.00 ft, Jun 22, 19720
BowieMD19.027.90 ft, Jun 22, 19720
Unity this gaugeMD8.018.60 ft, Sep 11, 19711

Other gauges in Montgomery County

Flood gauges in Montgomery County
Sandy Spring6.59.24 ft, Jan 19, 19960
Kemp Mill9.015.89 ft, Jun 22, 19720
Brighton Dam9.011.88 ft, Jan 31, 20130
Edwards Ferry15.022.45 ft, Jun 5, 20180
Washington DC (Little Falls)10.022.03 ft, Jun 24, 19724
Dawsonville7.516.40 ft, Jun 22, 19722
Takoma Park5.57.52 ft, Jul 19, 20250
Boyds7.09.68 ft, Sep 8, 20110
Clarksburg7.08.27 ft, Jul 30, 20160
Aspen Hill10.012.78 ft, Aug 12, 20100

Montgomery County: every hazard · River floods across the country · Maryland

NOAA National Water Prediction Service, gauge PRUM2, retrieved October 30, 2026. Stages in feet on the gauge's own datum, not elevation. Crests are as the National Weather Service lists them; preliminary values may be revised.