Scientific Investigations Report 2007–5159
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2007–5159
Re-evaluation of the 1921 Peak Discharge at Skagit River near Concrete, Washington
By M.C. Mastin
Table of Contents
Conversion Factors
Abstract
Introduction
Purpose and Scope
Field Survey of the 2003 Flood
Field Survey of the 2006 Flood
Calculated Water-Surface Slope for the 2006 Flood and the n Value for the 2003 Flood
Recalculating the 1921 Peak Discharge
Historic Peak Discharges Based on the Stage-Discharge Rating
Re-evaluating the Historic Peak Discharges
Summary
References Cited
Figures
Figure 1. Topographic map of the slope-area measurement reach on the Skagit River near Concrete showing the three cross sections (XS1, XS2, and XS3), the streamflow-gaging station, and HWMs from the 2003 flood and the 2006 flood surveyed by the U.S. Geological Survey.
Figure 2. High-water marks (HWMs) from peak flow of November 6, 2006, that was surveyed November 21, 2006, by the U.S. Geological Survey on the right bank between cross sections 2 (XS2) and 3 (XS3) on the Skagit River about 3,000–5,000 feet downstream of the streamflow-gaging station, Skagit River near Concrete, Washington (station No. 12194000).
Figure 3. Cross section XS2 as surveyed in 1923 and 2004, n values for the particular subareas (n), peak water surface for the 1921 and 2003 floods, and the points at which the cross sections were subdivided into two subareas. [Note: Stationing for the 1923 surveyed cross section was adjusted to fit the stationing surveyed in 2004.]
Figure 4. Historical photographs showing only small, sparse brush on the island/bar near cross section 2, Skagit River, Washington. Historical photographs on file at the U.S. Geological Survey, Washington Water Science Center.
Figure 5. High-water marks (HWMs), cross sections (XS), and water-surface profile from the peak flow of November 27, 1949 on the Skagit River about 3,000–5,000 feet downstream of the streamflow-gaging station, Skagit River near Concrete, Washington (station No. 12194000).
Figure 6. Cross sections B, C, and D and the n values (n) used in the n-verification study based on the 1949 peak discharge at Skagit River near Concrete, Washington.
Figure 7. Stage-discharge rating based on revised 1921 peak discharge recalculation extended to a gage height of 69.3 feet and the current stage-discharge rating for Skagit River near Concrete, Washington, showing selected discharge measurements, published historical peak discharges, and the proposed revised historic peak flows.
Tables
Table 1. Revised peak discharges for Skagit River near Concrete, Washington.
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Send questions or comments about this report to the author, M.C. Mastin, (253) 552-1609.
For more information about USGS activities in Washington, visit the USGS Washington Water Science Center home page.
U.S. Department of the Interior | U.S. Geological Survey