U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 03-4114
Estimating Annual High-Flow Statistics and Monthly and Seasonal Low-Flow Statistics for Ungaged Sites on Streams in Alaska and Conterminous Basins in Canada
Prepared in cooperation with
ALASKA DEPARTMENT OF TRANSPORTATION
AND PUBLIC FACILITIES
By Jeffrey B. Wiley and Janet H. Curran
Methods for estimating daily mean flow-duration statistics for seven regions in Alaska and low-flow frequencies for one region, southeastern Alaska, were developed from daily mean discharges for streamflow-gaging stations in Alaska and conterminous basins in Canada. The 15-, 10-, 9-, 8-, 7-, 6-, 5-, 4-, 3-, 2-, and 1-percent duration flows were computed for the October-through-September water year for 222 stations in Alaska and conterminous basins in Canada. The 98-, 95-, 90-, 85-, 80-, 70-, 60-, and 50-percent duration flows were computed for the individual months of July, August, and September for 226 stations in Alaska and conterminous basins in Canada. The 98-, 95-, 90-, 85-, 80-, 70-, 60-, and 50-percent duration flows were computed for the season July-through-September for 65 stations in southeastern Alaska. The 7-day, 10-year and 7-day, 2-year low-flow frequencies for the season July-through-September were computed for 65 stations for most of southeastern Alaska. Low-flow analyses were limited to particular months or seasons in order to omit winter low flows, when ice effects reduce the quality of the records and validity of statistical assumptions.
Regression equations for estimating the selected high-flow and low-flow statistics for the selected months and seasons for ungaged sites were developed from an ordinary-least-squares regression model using basin characteristics as independent variables. Drainage area and precipitation were significant explanatory variables for high flows, and drainage area, precipitation, mean basin elevation, and area of glaciers were significant explanatory variables for low flows. The estimating equations can be used at ungaged sites in Alaska and conterminous basins in Canada where streamflow regulation, streamflow diversion, urbanization, and natural damming and releasing of water do not affect the streamflow data for the given month or season. Standard errors of estimate ranged from 15 to 56 percent for high-duration flow statistics, 25 to greater than 500 percent for monthly low-duration flow statistics, 32 to 66 percent for seasonal low-duration flow statistics, and 53 to 64 percent for low-flow frequency statistics.
Description of Study Area
Determination of Drainage-Basin Characteristics
Determination of Streamflow Analysis Regions
Flow Statistics for Streamflow-Gaging Stations
Estimating Flow Statistics for Ungaged Sites
Procedures for Estimating Flow Statistics
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Other downloadable data:
Statistics High-flow statistics EXCEL Monthly low-flow statistics EXCEL Seasonal low-flow statistics EXCEL
Equations High-flow regressions EXCEL Monthly low-flow regressions EXCEL Seasonal low-flow regressions EXCEL
Characteristics Range of basin characteristics, for high-flow statistics EXCEL Range of basin characteristics, for low-flow statistics EXCEL
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For additional information contact:
Alaska Science Center, Water Resources Office
U.S. Geological Survey
4230 University Drive, Suite 201
Anchorage, AK 99508-4664
Please visit http://alaska.usgs.gov/ for more information about USGS activities in Alaska.
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Last modified: Thursday, September 01 2005, 05:09:18 PM