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The USGS conducts various studies of streamflow statistics for data collected at streamflow-gaging stations. Streamflow statistics for gaged streams and methods for estimating those statistics for ungaged streams are used by water resource planners and managers for designing infrastructure, managing floodplains, and protecting life, property, and aquatic resources. The most recent USGS studies of streamflow statistics for Alaska are presented in reports on flood frequency, flow duration, low-flow frequency, and streamflow record extension.
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Methods for accessing data and estimating streamflow statistics for Alaska are provided in USGS reports and, for selected locations, in the online StreamStats tool. These studies use data from USGS streamflow data-collection stations, available online at NWISWeb.
Flood frequency analysis uses a series of annual peak-streamflow, or flood, data recorded for a stream to develop a statistical expression of flood probability for that stream, such as the 1-percent chance flood (sometimes called the 100-yr flood). Regression equations relating flood frequency statistics for a group of gaged streams to physical or climatic characteristics of their respective drainage areas provide a tool for estimating flood frequency statistics at ungaged areas. The USGS most recently revised flood frequency regression equations for Alaska and conterminous basins in Canada in 2016.
Flow duration statistics, such as the 98-percent duration flow, describe the daily mean discharge in a stream that is exceeded a given percentage of the time. Low-flow frequency statistics, such as the 7-day, 2-yr low flow, refer to the discharge that occurs on a certain number of consecutive days that is associated with a certain exceedance probability. Regression equations relating these streamflow statistics for a group of gaged streams to physical or climatic characteristics of their respective drainage areas provide a tool for estimating the streamflow statistics at ungaged areas. The USGS has developed selected flow-duration and low-flow frequency regression equations for Alaska and conterminous basins in Canada.
StreamStats is a web-based application that facilitates access to data and computation tools and streamlines estimation of streamflow statistics. StreamStats is presently available in Alaska only for the Cook Inlet Basin. In addition to providing previously computed information for a streamgage location, Cook Inlet Basin StreamStats automates delineation of a drainage basin for a user-selected location, determination of the drainage area and mean annual precipitation, and computation of flood frequency estimates using those basin characteristics. The development of the Cook Inlet Basin StreamStats application is described in the most recent USGS Alaska flood-frequency report, U.S. Geological Survey Scientific Investigations Report 2016-5024.
Daily streamflow values for a short-record streamgage can be estimated from data for a longer-record index streamgage when the daily values for the overlapping period are closely correlated. Streamflow record extension creates a continuous string of daily values at the short-record streamgage for the period of record of the longer-record streamgage.
The USGS has approved streamflow records extension data for selected gaged streams. The data, methods of analysis, and accuracy of the estimated discharges are available in the accompanying reports.
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NWISWeb provides real-time and historic surface water data for USGS streamgages.
The National Water Information System (NWIS) web application provides access to real-time and historical surface-water, groundwater, water-quality, and water-use data collected at approximately 1.5 million sites across all 50 states.
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StreamStats provides access to spatial analytical tools that are useful for water-resources planning and management, and for engineering and design purposes. The map-based user interface can be used to delineate drainage areas, get basin characteristics and estimates of flow statistics, and more. Available information varies from state to state.
The NWIS mapper provides access to over 1.5 million sites contained in the USGS National Water Information System (NWIS), including sites where current and historical surface-water, groundwater, springs, and atmospheric data has been collected. Users can search by site type, data type, site number, or place.
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