This summary is published as USGS Fact Sheet 2013-3026 and can be downloaded as a PDF file

Streamflow of 2012 - Water Year Summary

U.S. Geological Survey
Reston, Virginia

January 2013

National Overview
Regional Patterns
Seasonal Characteristics
High and Low Flows

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 1930-2012, 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

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 69^th 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.

Streamflow was at record low levels (ranking 83^rd 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 streamflow in the normal range.

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

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.

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 season (October-December) streamflow was at record high levels (ranking 1^st in 83 years) in Ohio. Above 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 and much-below normal streamflows. Nationwide, autumn season streamflow ranked 21^st out of 83 years. * For Puerto Rico, 69 years of available data were used.
		Winter season (January-March) streamflow was at record low levels in Georgia and Florida. Above or much-above normal streamflow was 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 52^ndout of 83 years. *For Puerto Rico, 69 years of available data were used.
		Spring season (April-June) streamflow was below or much-below normal in most states (37 states). Above-normal streamflow was seen only in Washington, Oregon, and Puerto Rico. On a nationwide basis, spring season streamflow was much-below normal, ranking 81^stin 83 years. * For Puerto Rico, 69 years of available data were used.
		Summer season (July-September) streamflow in midwestern and southeastern states -- as well as Delaware, Vermont and New Hampshire -- was below or much-below normal. Streamflow in Kansas and Nebraska was 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 76^th in 82 years. * For Puerto Rico, 69 years of available data were used.

High and Low Flows

In any given month, on average, it is expected that five percent of the streamgages will experience very high (>95^th percentile) and very low (<5^th percentile) average streamflow. During water year 2012, only three 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).

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 one year was 69 percent, which occurred in 1996.

percentage above 10th percentile of annual 7-day minimum streamflow

The 10^th percentile 7-day low flow is defined as the lowest 7-day average streamflow expected to occur, on average, once in every 10 years. In water-year 2012, 12 percent of the streamgages reported a 7-day low flow less than the 10^th 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, which occurred in 1954.

Additional Information

The USGS operates a network of nearly 10,000 streamgages nationwide, most in real-time. Current information derived from these stations is available on the web at http://waterwatch.usgs.gov. Tables of data that summarize historical streamflow conditions by State, beginning in the year 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, see http://water.usgs.gov/nsip/.

For additional information, contact:
	Harry Lins U.S. Geological Survey 415 National Center Reston, VA 20192 Email: hlins@usgs.gov