January-December 2005 Streamflow

Introduction

The maps and graphs appearing in this summary describe streamflow conditions for 2005 in the context of the 76-year period 1930-2005, unless otherwise noted. The illustrations are based on observed data from the U.S. Geological Survey’s National Streamflow Information Program. Prior to 1930, the number of streamgaging stations was too small to provide representative data for computing statistics for most regions of the country. Reference is also made to runoff, which is the depth to which the country’s drainage area would be covered if all the streamflow for the year were uniformly distributed on it. Runoff is a simple estimate of the absolute magnitude of water flowing through the Nation’s rivers and streams.

National Overview

Annual Average U.S. Runoff, 1930-2005

Runoff from the land surface and the resultant flow in the Nation’s rivers and streams during 2005 was above the long-term annual average for the United States. Nationwide, 2005 streamflow was the 22nd highest during the 76-year period 1930-2005. Estimated annual runoff for 2005 across the conterminous U.S. was 17.1 inches, 1.6 inches above the 1930-2005 average.

2005 Statewide Streamflow Ranks
1930-2005

Above normal streamflow characterized most of the Southwest, Northeast, and parts of the Southeast, while below normal streamflow was prevalent in the Pacific Northwest, Wisconsin, and Louisiana. Maine recorded its highest annual average streamflow since 1930, while New Hampshire, New York, Maryland, Delaware and North Carolina reported their second-highest annual streamflow for the same period. Washington State experienced its sixth lowest annual streamflow.

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.

2005 Ranks by Water Resources Region
1930-2005

In 2005, the most notable regional streamflow variations were observed along the East and West Coasts. The New England region, for example, recorded its highest annual average streamflow since 1930, reflecting the record high precipitation that fell on this area during the year. Much above-normal streamflow was observed in the coastal drainages of the Mid-Atlantic and South Atlantic-Gulf regions, as well as in the Lower Colorado region. Below normal streamflow occurred in the Pacific Northwest and Lower Mississippi regions, the latter not receiving enough precipitation from Hurricanes Katrina or Rita to offset the precipitation deficits that occurred during much of the year. Most of the interior drainages of the Nation experienced normal streamflow for the year.

Seasonal Characteristics

Winter (January-March) Statewide Ranks

Winter season (Jan-Mar) streamflow was slightly above normal for the Nation, ranking as the 19th highest in 76 years. Much above normal streamflow occurred across the southern Great Lakes states, Utah, Arizona, and Puerto Rico, while much below normal streamflow prevailed in Oregon.

Spring (April-June) Statewide Ranks

Spring season (Apr-Jun) streamflow was normal (43rd highest in 76 years) nationwide, although there were much above normal conditions scattered along the Eastern Seaboard coupled with below normal conditions stretching from the Great Lakes to Texas as well as in much of the Pacific Northwest.

Summer (July-September) Statewide Ranks

Summer season (Jul-Sep) streamflow was in the normal range for the U.S., ranking 28th out of 76 summer seasons in the record. Alabama registered its highest summer season streamflow, while Washington had its third lowest and Wisconsin its fifth lowest summer streamflow.

Autumn (October-December) Statewide Ranks

Autumn season (Oct-Dec) streamflow increased significantly across the western U.S. and the Northeast, leading to above normal conditions nationwide (10th highest autumn flows in 76 years). Eight states reported new record high autumn streamflow: Montana, Wyoming, Maine, New Hampshire, Vermont, Massachusetts, Maryland, and Delaware.

High and Low Flows

Percentage of Streamgaging Stations With Very High and Very Low Monthly Streamflows
January 2000 - December 2005

In any given month, on average, it is expected that five percent of the streamgaging stations will experience very high (>95th percentile) or very low (<5th percentile) average streamflow. In January 2005, 22 percent of streamgaging stations had very high average streamflow, or more than four times the expected number. In October and December, 10 percent and 8 percent of the streamgaging stations, respectively, reported very high average flows. In contrast, the number of streamgaging stations reporting very low streamflow was at or below that expected for each month of the year.

Number of Record High Daily Mean Flow
1950-2005

Similarly, in any given year, on average, it is expected that one percent of the streamgaging stations will experience a new all-time record high or all-time record low streamflow. In 2005, two percent of USGS streamgaging stations reported new record high streamflow. The largest number of new record highs in any one year since 1950, six percent of the gages, occurred in 1997.

Number of Record 7-Day Low Flows
1950-2005

At the other extreme, three percent of the streamgaging stations reported new record 7-day low flows in 2005. The 7-day low flow is defined as the lowest average streamflow to occur on seven consecutive days in a year. Notably, however, the number of new record low streamflows that have been set annually since 1999 (the year when the current period of widespread drought began in the U.S.) has been well-below the number of records set during previous multi-year drought periods in the 1950s and 1960s. In 1954, for example, eight percent of the streamgaging stations set new all-time record 7-day low flows, the largest number in any year since 1950.

Flooding

Number of Streamgaging Stations Reporting Flooding
1950-2005

Flooding in 2005 occurred at 54 percent of the streamgaging stations in the conterminous U.S., slightly above the long-term average of 50 percent. This is the first year since 1998 when the number has exceeded the long-term average, and most likely reflects a decrease in the area of the country affected by severe drought.

Additional Information

The USGS operates a network of nearly 7,000 streamgaging stations nationwide, many in real-time. Current information derived from these stations is available on the web at http://water.usgs.gov/waterwatch. 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 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 800 agencies at the Federal, State, Tribal, and local levels.

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