Streamflow of 2005 - Annual Summary
U.S. Geological Survey
|January-December 2005 Streamflow
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.
|Annual Average U.S.
| Runoff from the land surface and the resultant flow in the Nationís
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
|2005 Statewide Streamflow
|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.
|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
|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.
|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
|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
|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 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
|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
|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.
|Number of Streamgaging
Stations Reporting Flooding
|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.
|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