Streamflow record extension for selected streams in the Susitna River Basin, Alaska

Abstract

Tables Table 1. Basin characteristics for selected streams in and near the Susitna River Basin, Alaska …………………………………………………………………………… 4 Table 2. Correlation coefficients (Pearson's r) between logarithms of daily discharge values at sites of interest and potential index stations for streams in the Susitna River Basin, Alaska ……………………………………………………………… 9 Table 3. Values for variables, discharge input ranges, and measures of error for equations for estimating daily discharge from index station data at selected streamgages, Susitna River Basin, Alaska ……………………………………………………… 12 Table 4. Periods of observed and extended streamflow records and index stations used for record extension for selected streamgages, Susitna River Basin, Alaska …… 15 Table 5. Mean monthly discharge for composite (observed and extended) records for selected streamgages in the Susitna River Basin, Alaska, water years 1950-2010 ………………………………………………………………………… 17 Table 6. Difference in mean monthly discharge between composite (observed and extended) records and observed records for selected streamgages in the Susitna River Basin, Alaska, water years 1950-2010 ……………………………… 17 Table 7. Annual mean discharge for composite (observed and extended) records for selected streamgages in the Susitna River Basin, Alaska, water years 1950-2010 ………………………………………………………………………… 18 Table 9. Nash Sutcliffe efficiency (NSE) coefficients comparing observed and predicted discharge values at selected streamgages in the Susitna River Basin, Alaska …………………………………………………………………………… 20 AbstractDaily streamflow records for water years 1950-2010 in the Susitna River Basin range in length from 4 to 57 years, and many are distributed within that period in a way that might not adequately represent long-term streamflow conditions. Streamflow in the basin is affected by the Pacific Decadal Oscillation (PDO), a multi-decadal climate pattern that shifted from a cool phase to a warm phase in 1976. Records for many streamgages in the basin fell mostly within one phase of the PDO, such that monthly and annual statistics from observed records might not reflect streamflow conditions over a longer period. Correlations between daily discharge values sufficed for extending streamflow records at 11 of the 14 streamgages in the basin on the basis of relatively long-term records for one or more of the streamgages within the basin, or one outside the basin, that were defined as index stations. Streamflow at the index stations was hydrologically responsive to glacier melt and snowmelt, and correlated well with flow from similar high-elevation, glaciated basins, but flow in low-elevation basins without glaciers could not be correlated to flow at any of the index stations. Kendall-Theil Robust Line multi-segment regression equations developed for one or more index stations were used to extend daily discharge values to the full 61-year period for all 11 streamgages. Monthly and annual statistics prepared for the extended records show shifts in timing of breakup and freeze-up and magnitude of snowmelt peak...

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