The maps and graphs in this summary describe national streamflow conditions for water year 2017 (October 1, 2016, to September 30, 2017) in the context of streamflow ranks relative to the 88-year period of 1930–2017, unless otherwise noted. The illustrations are based on observed data from the U.S. Geological Survey (USGS) National Streamflow Network (U.S. Geological Survey, 2018a). The period of 1930–2017 was used because the number of streamgages before 1930 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 period was uniformly distributed on it. The value of 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. In this summary, runoff for a specified period and geographic area is computed from all streamgages with complete record in the geographic area.
In all the graphics, a rank of 1 indicates the highest annual flow of all years analyzed and 88 indicates the lowest annual flow of all years. Rankings of streamflow are grouped into much below normal, below normal, normal, above normal, and much above normal based on percentiles of flow (less than 10 percent, 10–24 percent, 25–75 percent, 76–90 percent, and greater than 90 percent, respectively; U.S. Geological Survey, 2018b). States or water-resources regions are presented in the text in order of ranking; a highest or lowest rank is not shown when there are ties in the rankings. Some of the data used to produce the maps and graphs are provisional and subject to change.
Annual runoff in the Nation’s rivers and streams during water year 2017 (10.86 inches) was higher than the long-term (1930–2017) mean annual runoff of 9.33 inches for the contiguous United States (fig. 1). Nationwide, the 2017 streamflow ranked 10th highest out of the 88 years.
Record low streamflow levels were reported in Alaska (fig. 2). Streamflow was below normal in Hawaii, Georgia, New Jersey, Connecticut, and Tennessee. Streamflow was above normal in Illinois, Vermont, Utah, Montana, Washington, New York, Iowa, Indiana, Idaho, and Puerto Rico and the Virgin Islands. Streamflow was much above normal in Minnesota, Oregon, Nevada, Michigan, California, Wisconsin, and Wyoming. Most States had streamflow in the normal range.
The United States (including Puerto Rico and the Virgin Islands and the District of Columbia) is divided into 21 large drainages, or water-resources regions (fig. 3). These water-resources regions are based on surface topography and contain the drainage area of a major river; the combined drainage areas of a series of rivers, such as the Texas-Gulf region, which includes several 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.
Streamflow was reported at record low levels in the Alaska region (fig. 4). Below normal streamflow was reported in the Hawaii and Tennessee regions. Streamflow was above normal in the Souris-RedRainy, Caribbean, and Upper Mississippi regions. Much above normal streamflow was reported in the Great Basin, Pacific Northwest, California, and Great Lakes regions.
The USGS operated a nationwide network of more than 8,200 streamgages in 2017, and almost all USGS streamgages are operated in real time. Current (2018) information derived from these stations is available at https://waterwatch.usgs.gov. Tables of data that summarize historical streamflow conditions by State, expressed as runoff, beginning in water year 1901, can be accessed at https://waterwatch.usgs.gov/?id=statesum. These tables are updated every few months to reflect the most current streamflow data. The streamflow information used to prepare this summary also is used for water management, flood and drought monitoring, bridge design, and several recreational activities. To obtain real-time and archived streamflow data and information, visit https://doi.org/10.5066/F7P55KJN. The National Streamflow Network, which is part of the Groundwater and Streamflow Information Program, is operated primarily by the USGS; however, funding for operating the network is provided by the USGS and about 850 Federal, State, tribal, regional, and local partners. Access additional streamflow information online at https://www.usgs.gov/gwsip.
U.S. Geological Survey, 2018a, Groundwater and Streamflow Information Program: U.S. Geological Survey web page, accessed June 2018 at https://www.usgs.gov/water-resources/groundwater-and-streamflow-information.
U.S. Geological Survey, 2018b, Map of real-time streamflow compared to historical streamflow for the day of the year (United States): U.S. Geological Survey web page, accessed June 2018 at https://waterwatch.usgs.gov/?id=ww_current.
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