U.S. Department of the Interior

U.S. Geological Survey

FS–2012–3085

August 2012

Streamflow of 2011—Water Year Summary

U.S. Geological Survey

Reston, Virginia

January 2012

•	Introduction

•	National Overview

•	Regional Patterns

•	Seasonal Characteristics

•	High and Low Flows

Dry Normal Wet

2011 statewide streamflow

Introduction

The maps and graphs in this summary describe streamflow conditions for water year 2011 (October 1, 2010,

to September 30, 2011) in the context of the 82-year period from 1930 through 2011, unless otherwise noted.

The illustrations are based on observed data from the U.S. Geological Survey’s (USGS) National Streamflow

Information Program (http://water.usgs.gov/nsip/). The period 1930–2011 was used because, prior to 1930, the

number of streamgages was too small to provide representative data for computing statistics for most regions of

the country.

In the summary, reference is made to the term “runoff,” which is the depth to which a river basin, State, or other

geographic area would be covered with water if all the streamflow within the area during a single year was

uniformly distributed upon it. Runoff quantifies the magnitude of water flowing through the Nation’s rivers and

streams in measurement units that can be compared from one area to another.

Each of the maps and graphs below can be expanded to a larger view by clicking on the image. In all the

graphics, a rank of 1 indicates the highest flow of all years analyzed.
National Overview

Mean runoff in the Nation’s rivers

and streams during 2011 (10.50

inches) was higher than the longterm annual mean for the United

States (9.31 inches). Nationwide,

2011 streamflow ranked 16th out of

the 82 years in period 1930–2011.

Note that in previous water year

summaries the median runoff, not

the mean runoff, was compared

among time periods.

Streamflow was at record high levels (ranking first in 82 years) in the

States of Montana, North Dakota,

South Dakota, Minnesota, New

York, and Vermont. Above-normal

and much-above-normal streamflow

characterized the remaining States

in the Northeast, North, West, and

Puerto Rico. In contrast, streamflow

was at record low levels (ranking 82d

in 82 years) in Texas and Alaska.

Below-normal and much-belownormal streamflow was prevalent

cross the Southeast and South. Only

11 States had streamflow in the

normal range.

* For Puerto Rico, 68 years of

available data were used.

1930 1940 1950 1960 1970 1980 1990 2000 2010

Year

0

5

10

15

Annual mean runoff (inches)

0

5

10

15

Annual mean U.S. runoff

1930–2011

18

11

1 2 1

19 8 1

8 1

33

1

2

14

10

7 2

6

6 3 10 8 24 27 47 65 23 11

69

74

68

34 62

82

46 80

79 72 72

81

81

82

37

2*

1

2011 statewide streamflow ranks (1930–2011)

VT

NH

MA (12)

RI(43)

CT(6)

NJ(2)

DE(41)

MD(22)

DC(4)

AK

HI

PR-VI

Explanation - Rank

82 75–81 63–74 9–20 12–8

Highest

Much

above

normal

Above

normal Normal Belownormal

Much

below

normal

Lowest

21–62
Regional Patterns

The United States (including Puerto

Rico) is divided into 21 large drainages, or water resources regions.

These hydrologic areas are based

on surface topography and contain

either the drainage area of a major

river, such as the Columbia, the

combined drainage areas of a series

of rivers, such as the Texas-Gulf

region, which includes a number of

rivers draining into the Gulf of Mexico, or the area of an island or island

group. Water resources regions

provide a coherent, watershed-based

framework for depicting streamflow

variations.

Water resources regions of the United States

Streamflow was at record high

levels (ranking first in 82 years) in

the water resource regions in the

Souris-Red-Rainy and Mid-Atlantic

regions. Above-normal and muchabove-normal streamflow occurred

in all northeastern, northern, and

western regions, and in the Caribbean. In contrast, streamflow was

at record low levels (ranking 82d in

82 years) in the South Atlantic-Gulf,

Texas-Gulf, and Alaska regions,

respectively. Below-normal and

much-below-normal streamflows

were reported in the Lower Mississippi, and Rio Grande regions.

11

3

5 1

7 6

1

13

10

15 9

59 56

81 82

42

70

82 82

52

2*

PR-VI

HI

AK

Explanation - Rank

82 75–81 63–74 9–20 12–8

Highest

Much

above

normal

Above

normal Normal Belownormal

Much

below

normal

Lowest

21–62
Seasonal Characteristics

Autumn season (October–Decem- ber) streamflow was at records high

levels (ranking first in 82 years) in

the States of North Dakota, South

Dakota, and Minnesota. Above- and

much-above-normal flows were

reported in northeastern, northern,

and southwestern States. Florida had

record low flow (ranking 82d in

82 years). Most of the other south- eastern and southern States, as well

as Alaska, had below- and muchbelow-normal streamflows. Nation- wide, autumn season streamflow

ranked 44th out of 82 years.

* For Puerto Rico, 68 years of

available data were used.

30

40

46 3

1

1

28 11 4

12 7 52 1 48

14

9 14 20

32

17 51 48 62 45 64 54 51 54 53

50

41

56 57 74

74

76 79

72 74 74

80

82

74

20

Autumn (October–December 2010) statewide ranks

12*

VT

NH

MA (31)

RI(43)

CT(40)

NJ(52)

DE(40)

MD(46)

DC(40)

AK

HI

PR-VI

Winter season (January–March)

streamflow was above to much

above-normal in many northern and

northeastern States. Record low flow

(ranking 82d in 82 years) occurred

in Alaska. Below-normal and muchbelow-normal streamflow occurred

in the most southern and south- eastern States. Nationwide, winter

season streamflow ranked 31st out

of 82 years.

* For Puerto Rico, 68 years of

available data were used.

15

18

8 6

3 16 34 22 18

10 11

46 4

19

24

16 12 12

18 26 15 28 28 40 34 61 2841 42

61

74

62

55 76

79

75 81

67 74 73 78

78

82

42

Winter (January–March 2011) statewide ranks

39*

41

VT

NH

MA (20)

RI(57)

CT(17)

NJ(20)

DE(59)

MD(52)

DC(40)

AK

HI

PR-VI

Explanation - Rank

82 75–81 63–74 9–20 12–8

Highest

Much

above

normal

Above

normal Normal Belownormal

Much

below

normal

Lowest

21–62
Spring season (April–June) streamflow was at record high levels (ranking 1st in 82 years) in the States

of Montana, South Dakota, North

Dakota, Illinois, Indiana, Ohio,

Kentucky, and Vermont. Streamflow was above or much above

normal in the northern and western

States, Missouri, Arkansas, Tennessee, Hawaii, and Puerto Rico. In

contrast, southeastern and southern

States reported below- or muchbelow-normal flows; streamflow in

Texas was at record low levels. On

a nationwide basis, spring season

streamflow was much above normal,

ranking fifth in 82 years.

* For Puerto Rico, 68 years of

available data were used.

14

8

1 18

3 1 4 13

6 1

10 2

6 1 4

15

17

14 2

10

20 1 1 1 26 9 29 56 8 1

66

68

68 3 37

82

6 71

71 5657

79

80

71

19

5*

Spring (April–June 2011) statewide ranks

VT

NH

MA (36)

RI(43)

CT(13)

NJ(15)

DE(57)

MD(26)

DC(44)

AK

HI

PR-VI

Summer season (July–September)

streamflow was at record high levels

(ranking 1st in 82 years) in the

States of Montana, North Dakota,

Wyoming, Idaho, New Jersey, New

York, and Vermont. This was the

third season out of four that North

Dakota experienced record high lev- els. Streamflow was above or much

above normal in the northeastern,

northern, northwestern and western

States, and Puerto Rico. In contrast,

southeastern and southern States and

Alaska reported below- or muchbelow-normal flows. Streamflow in

Georgia was at record low levels. On

a nationwide basis, summer season

streamflow was much above normal,

ranking 13th in 82 years.

* For Puerto Rico, 68 years of

available data were used.

15

1

1 8

5 1

5 5 1

23 1

40 2 1

4

5 26 3

4

11 1 14 22 37 6 46 40 21 67 25

69

58

79 51 73

81

21 79

27 61 82

68

77

79

29

Summer (July–September 2011) statewide ranks

3*

VT

NH

MA (2)

RI(5)

CT(2)

NJ(1)

DE(6)

MD(5)

DC(5)

AK

HI

PR-VI

Explanation - Rank

82 75–81 63–74 9–20 12–8

Highest

Much

above

normal

Above

normal Normal Belownormal

Much

below

normal

Lowest

21–62
High and Low Flows

10

20

30

0

10

20

30

2000 2002 2004 2006 2008 2010

Year

30

20

10

0

30

20

10

0

Percentage of streamgages

Percentage of streamgages with very high and very low monthly streamflow

October 1999–September 2011

>95th percentile for month

 <5th percentile for month

In any given month, on average, it is expected that 5 percent of the streamgages will experience very high

(>95th percentile) and very low (<5th percentile) average streamflow. During water year 2011, 9 months

(October, December, March, April, May, June, July, August, and September) had a greater than expected

percentage of streamgages reporting very high streamflow (6, 6, 12, 16, 15, 11, 14, 14, and 15 percent respectively). In contrast, there were 5 months (May, June, July, August, and September) with a greater than expected

percentage of streamgages with very low flows (6, 9, 7, 7, and 6 percent, respectively).
The bankfull streamflow is defined

as the highest daily mean streamflow value expected to occur, on

average, once in every 2.3 years.

In 2011, 50 percent of streamgages

had a daily mean streamflow value

above the bankfull level. This value

is greater than the expected number

(43 percent) to occur in any given

year. Since 1950, the largest number

of streamgages reporting higher than

bankfull streamflow in any 1 year

was 68 percent, which occurred in

1996.

1950 1960 1970 1980 1990 2000 2010

Year

0

10

20

30

40

50

60

70

80

90

100

Percentage of streamgages

0

10

20

30

40

50

60

70

80

90

100

Percentage of streamgages above bankfull streamflow

1950−2011

The 10th percentile 7-day low flow

is defined as the lowest 7-day average streamflow expected to occur,

once every 10 years. In water year

2011, 17 percent of the streamgages

reported a 7-day low flow less than

the 10th percentile 7-day low flow.

The expected number to occur in

any given year is 10 percent. Since

1950, the largest percentage of

streamgages reporting a 7-day low

flow less than the 10th percentile

7-day low flow was 25 percent in

1954.

1950 1960 1970 1980 1990 2000 2010

Year

0

5

10

15

20

25

30

Percentage of streamgages

0

5

10

15

20

25

30

Percentage of streamgages below 10th percentile of

annual 7-day minimum streamflow 

1950–2011
Additional Information

The USGS operates a network of nearly 10,000 streamgages

nationwide, many in real time. Current information derived from

these stations is available at http://waterwatch.usgs.gov. Tables

of data that summarize historical streamflow conditions by State,

beginning in 1900, can be accessed at

http://waterwatch.usgs.gov/?m=statesum. These tables are updated

every few months to reflect the most current streamflow data.

The streamflow information used to prepare this summary is also

used for water management, monitoring floods and droughts,

bridge design, and for many recreational activities. To obtain realtime and archived streamflow data and information, visit

http://water.usgs.gov/nwis. Although the national streamgage network is operated primarily by the USGS, it is funded by a partnership of 850 agencies at the Federal, State, tribal, and local levels.

For more information about the streamgage network, visit

http://water.usgs.gov/nsip/.

By Xiaodong Jian, David M. Wolock, 

Harry F. Lins, and Steve Brady

For additional information, contact:

	 Harry Lins

	 U.S. Geological Survey

	 415 National Center

	 Reston, VA 20192

	 Email: hlins@usgs.gov

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