Selected Special Conditions Affecting Peak Streamflow and Extreme Floods in Alaska Through Water Year 2022
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- Document: Report , HTML , XML
- Data Releases:
- USGS data release - Selected peak-flow special conditions for USGS streamgages in Alaska (ver. 2.0)
- USGS data release - Selected basin boundaries for USGS streamgages in Alaska through 2014
- USGS data release - Selected basin boundaries for USGS streamgages in Alaska through 2019
- USGS data release - Summary of selected basin and streamflow special conditions for USGS streamgages in Alaska
- USGS data release - Extreme flood, atmospheric river presence, and basin characteristic data for a study of peak streamflow special conditions in Alaska
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Abstract
The U.S. Geological Survey, in cooperation with the Alaska Department of Transportation and Public Facilities, inventoried selected special conditions for annual peak flows and identified extreme floods at streamgages in Alaska through water year 2022 to facilitate hydrologic analysis. Special conditions identified from U.S. Geological Survey gaging records and basin characteristics included regulation and diversion, urbanization, indeterminate drainage areas, drainage areas less than the minimum used in regional analyses, glacial lake outburst floods, other outburst floods, and snowmelt floods. For peak flows that occurred during calendar years 1980–2019, an atmospheric river dataset was used to identify atmospheric river presence or absence on the dates peak flows occurred. Extreme floods (defined as peak flows exceeding the 1-percent annual exceedance probability flood magnitude or an empirical measure of relative magnitude using Creager’s coefficient C) were identified and associated with flood-generating mechanisms using the other inventoried special conditions and other information.
The gaging record contained glacial lake outburst floods at 15 streamgages and other types of outburst floods at 10 streamgages. Non-outburst peak flows in Alaska resulted from a mixture of rainfall and melt-based flood-generating mechanisms in all but the most rain-dominated seasonal flow regime. Melt-based flood-generating mechanisms included snowmelt, high-elevation snow and ice melt, or rain-on-snow events. Atmospheric rivers were common in Alaska and conterminous basins in Canada, occurring in that region on 67 percent of the days in the calendar year 1980–2019 period. Atmospheric rivers were more common on the days of peak flows and even more common on the days of non-outburst extreme floods. The percentage of days when an atmospheric river was present increased to 78 percent for the days of peak flows in that period and to 83 percent for the days of non-outburst extreme floods in that period. Of 149 extreme floods in the gaging record, 38 were generated by outburst floods. Of the non-outburst extreme floods, 72 percent were generated by rainfall and 26 percent were generated by melt-based processes or a combination of rainfall and melt-based processes. Flood-generating mechanisms could not be determined for the final 2 percent of the non-outburst extreme floods because the month and day of the peak flows were unknown and no other information was available. Secondary factors strongly associated with extreme floods included antecedent rain and streamflow conditions and warm storm conditions that produced rain instead of snow or generated snowmelt.
Suggested Citation
Curran, J.H., 2025, Selected special conditions affecting peak streamflow and extreme floods in Alaska through water year 2022: U.S. Geological Survey Scientific Investigations Report 2025–5056, 41 p., https://doi.org/10.3133/sir20255056.
ISSN: 2328-0328 (online)
Study Area
Table of Contents
- Abstract
- Introduction
- Description of Study Area
- Data Collection and Compilation Methods
- Results of Inventories of Special Conditions for Peak Flows
- Results of Assessment of Flood-Generating Mechanisms for Extreme Floods
- Discussion—Applications for Hydrologic Analysis
- Limitations
- Summary
- References Cited
| Publication type | Report |
|---|---|
| Publication Subtype | USGS Numbered Series |
| Title | Selected special conditions affecting peak streamflow and extreme floods in Alaska through water year 2022 |
| Series title | Scientific Investigations Report |
| Series number | 2025-5056 |
| DOI | 10.3133/sir20255056 |
| Publication Date | July 17, 2025 |
| Year Published | 2025 |
| Language | English |
| Publisher | U.S. Geological Survey |
| Publisher location | Reston, VA |
| Contributing office(s) | Alaska Science Center Water |
| Description | Report: viii, 41 p.; 5 Data Releases |
| Country | United States |
| State | Alaska |
| Online Only (Y/N) | Y |