U.S. Department of the InteriorU.S. Geological Survey

FS 2013–3026May 2013

Streamflow of 2012—Water Year Summary

U.S. Geological SurveyReston, Virginia

May 2013

• Introduction• National Overview• Regional Patterns• Seasonal Characteristics• High and Low Flows

2012 Statewide streamflow

WetNormalDry

Introduction

The maps and graphs in this summary describe streamflow conditions for water year 2012 (October 1, 2011, to September 30, 2012) in the context of the 83-year period from 1930 through 2012, 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 1930–2012 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 specified time period 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

1930 1940 1950 1960 1970 1980 1990 2000 2010

Year

0

5

10

15

Ann

ual m

ean

runo

ff (in

ches

)

0

5

10

15

Annual mean U.S. runoff1930–2012

Average runoff in the Nation’s rivers and streams during 2012 (7.90 inches) was lower than the long-term annual mean for the United States (9.30 inches). Nationwide, 2012 streamflow ranked 69th out of the 83 years in the period 1930–2012. Note that in previous water year summaries (prior to 2011) the median runoff, not the average runoff, was compared among time periods.

2012 Statewide streamflow ranks1930–2012

AKHI

PR-VI

MA (45)RI (41)

CT (46)NJ (41)DE (56)MD (46)DC (47)

NHVT

28

28

25 2252

4833

60 4358

3858

62

603468

4561 1972 42

80 39 496466 45

7973

755655

63

41 82837460

4462

22

30

52 36

30*

Explanation - Rank 1 2–89–2064–7576–8283

Highest Muchabovenormal

AbovenormalNormal Below

normalMuchbelownormal

Lowest

21–63

Streamflow was at record low levels (ranking 83d in 83 years) in Georgia. Below-normal and much-below-normal streamflow was prevalent cross the Southeast, Midwest, and Southwest. Above-normal streamflow occurred only in Ohio. Most States had stream-flow in the normal range.

* For Puerto Rico, 69 years of available data were used.

Regional Patterns

Water resources regions of the United States

Water resourcesregions

The United States (including Puerto Rico) is divided into 21 large drain-ages, 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.

AKHI

PR-VI

28

61

3459

70 4547

6252

7436

7757

77 7759

555922

30

28*

Explanation - Rank 1 2–89–2064–7576–8283

Highest Muchabovenormal

AbovenormalNormal Below

normalMuchbelownormal

Lowest

21–63

Streamflows at much-below-normal levels were reported in the South Atlantic-Gulf, Rio Grande, and Lower Colorado regions. Below-normal conditions were measured in the Upper Mississippi and Upper Colorado regions.

Seasonal Characteristics

Autumn (October–December 2012) Statewide ranks

AKHI

PR-RI

MA (4)RI (3)

CT (4)NJ (4)DE (8)MD (8)DC (11)

NHVT

66

37

34 2057

271 415

41 920

312

64

13345

418 122 724 5 193453 7

6350

561532

71

10 8075535270

5034

46

36*

Autumn season (October–December) streamflow was at record-high levels (ranking first in 83 years) in Ohio. Above-normal and much-above-normal flows were reported in the Northeast, Great Lakes, and northern States, as well as a few western States. West coast States, Texas, Louisiana, Georgia, and South Carolina had below-normal and much-below-normal stream-flows. Nationwide, autumn season streamflow ranked 21st out of 83 years.

* For Puerto Rico, 69 years of available data were used.

Winter (January–March 2012) Statewide ranks

AKHI

PR-RI

MA (67)RI (70)

CT (64)NJ (69)DE (64)MD (61)DC (65)

NHVT

30

3634 28

4243

21 3929

36 4522

329

66

54 50659

38 3659 3231 45 555238 44

7273

564927

32

31 82836848

17

8345

29

9*

Explanation - Rank 1 2–89–2064–7576–8283

Highest Muchabovenormal

AbovenormalNormal Below

normalMuchbelownormal

Lowest

21–63

Winter season (January–March) streamflow was at record-low levels in Georgia and Florida. Below-normal and much-below-normal streamflows were reported in east coast States, California, Arizona, and Iowa. Above-normal conditions occurred in Wyoming, Utah, Louisiana, as well as Puerto Rico. Nationwide, winter season streamflow ranked 52d out of 83 years.

* For Puerto Rico, 69 years of available data were used.

Spring (April–June 2012) Statewide ranks

AKHI

PR-RI

MA (74)RI (72)

CT (70)NJ (71)DE (81)MD (76)DC (59)

NHVT

14

2922 56

4062

18 687558 798054

63

4575

755771

60 7671 7981 70 667067 79

8265

698274

73

81 81828281

69

5451

45

9*

Spring season (April–June) streamflow was below or much below normal in most States (37). Above-normal streamflow was seen only in Washington, Oregon, and Puerto Rico. On a nationwide basis, spring season streamflow was much below normal, ranking 81st in 83 years.

* For Puerto Rico, 69 years of available data were used.

Summer (July–September 2012) Statewide ranks

AKHI

PR-RI

MA (61)RI (56)

CT (60)NJ (47)DE (77)MD (54)DC (50)

NHVT

20

29

45 4154

5526 5267

78 6975

7470

49

385181

5483 6876 7581 59 558183 65

7455

81 6480

58

72 7177539

2520

53

41

46*

Explanation - Rank 1 2–89–2064–7576–8283

Highest Muchabovenormal

AbovenormalNormal Below

normalMuchbelownormal

Lowest

21–63

Summer season (July–September) streamflow in Midwestern and southeastern States—as well as Delaware, Vermont, and New York—was below or much below normal. Streamflows in Kansas and Nebraska were at record-low levels. Streamflow was above normal in Washington, Louisiana, and Florida. On a nationwide basis, summer-season streamflow was much below normal, ranking 76th in 83 years.

* For Puerto Rico, 69 years of available data were used.

High and Low Flows

0

10

20

30

0

10

20

30

2000 2004 2008 2012

Year

30

20

10

0

30

20

10

0

Perc

enta

ge o

f stre

amga

ge

Percentage of streamgages with very high and very low monthly streamflowOctober 1999–September 2012

2002 2006 2010

>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 2012, only 3 fall months (October, November, and December) had a greater-than-expected percentage of streamgages reporting very high streamflow (8, 7, and 8 percent, respectively). In contrast, there were 8 months (from February to September) with a greater-than-expected percentage of streamgages with very low flows (6, 6, 18, 8, 13, 13, 10, and 9 percent, respectively).

1950 1960 1970 1980 1990 2000 2010

Year

0

10

20

30

40

50

60

70

80

90

100

Perc

enta

ge o

f stre

amga

ges

0

10

20

30

40

50

60

70

80

90

100

Percent of streamgages above bankfull streamflow1950–2012

The bankfull streamflow is defined as the highest daily mean streamflow value expected to occur, on average, once in every 2.3 years. In 2012, 23 percent of streamgages had a daily mean streamflow value above the bankfull level. This value is much smaller 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 69 percent, which occurred in 1996.

1950 1960 1970 1980 1990 2000 2010

Year

0

5

10

15

20

25

30

Perc

enta

ge o

f stre

amga

ges

0

5

10

15

20

25

30

Percent of streamgages below 10th percentile ofannual 7-day minimum streamflow

1950–2012

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 2012, 12 percent of the streamgages reported a 7-day average low flow less than the 10th percentile 7-day low flow value. 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.

Additional Information

The USGS operates a network of nearly 8,000 streamgages nationwide, most 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 real-time 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:Office of Surface WaterU.S. Geological Survey415 National CenterReston, VA 20192http://water.usgs.gov/osw/

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