Revision History

Publication Series and Series Number:  Scientific Investigations Report 2005-5029

Publication Title:  Verification of 1921 Peak Discharge at Skagit River near Concrete,

Washington, Using 2003 Peak-Discharge Data

Publication Authorship:  M. C. Mastin and D. L. Kresch

First Version and Date of First Release:  1.0  March 8, 2005

Current Version and Date of Current Release:  2.0  August 2005

Summary of Product Components

Component	Description	Last Revised in Pub Version	Date of Last Revision
Book	Verification of 1921 peak discharge at Skagit River near Concrete, Washington, using 2003 peak discharge data	2.0	August 9, 2005

Historical List of Revisions (latest revision first)

Version 2.0—August 2005

 Cover 1—Addition of “Version 2.0, August 2005” under report series and number.

Title page—Addition of “Version 2.0, August 2005” under report series and number.

On page 1—Second paragraph, first sentence rewritten as “The four largest annual peak discharges used in the determination of the 100-year flood discharge at Skagit River near Concrete occurred in 1897, 1909, 1917, and 1921.“

On page 1—First paragraph under INTRODUCTION:

Third sentence rewritten as “The 100-year flood, the primary design flood used for these projects is based on the historical peak discharges at Skagit River near Concrete, Wash….inadequate protection measures.”

New 4^th sentence added: “Station 12194000 is used to determine the design flood because it has a long period of record, has a stable stage-discharge rating curve, and is downstream of all major tributaries in the Skagit River basin.”

Second paragraph under INTRODUCTION, second sentence, “Pursuant…, recently has completed a draft…”, was rewritten as, “Pursuant…, recently completed a draft…”

Third sentence, “A critical…probability the—100-year flood.” was rewritten as “A critical…probability—the 100-year flood.”

Fourth sentence, “Annual peak discharges…1917, and 1921.” was replaced with “A log-Pearson Type III flood-frequency analysis of all available unregulated annual peak discharges at Skagit River near Concrete was used to determine the 100-year flood discharge.

A new paragraph was added following the fourth sentence:

The Skagit River near Concrete gaging station was established as a continuous record station in 1924. However, because Skagit River flows have been regulated since 1924, all of the annual peak discharges determined since 1924 are affected by regulation. Estimates of the unregulated annual peak discharges for water years 1944–2004 were determined from the regulated annual peak discharges by USACE (Ted Perkins, U.S. Army Corps of Engineers, written commun., 2004) and used in the flood-frequency analysis. Unregulated annual peak discharges could not be determined for the 1925–43 water years because necessary streamflow data were not available. Also used in the flood-frequency analysis were peak discharges for historic floods in 1897, 1909, 1917, and 1921. Peak discharges for the 1815 (500,000 ft3/s) and 1856 (350,000 ft3/s) historic floods were downgraded to estimates and consequently not used in the flood-frequency analysis because the times and validity of the peak stages of these floods could not be validated (R.A. Kimbrough, U.S. Geological Survey, oral commun., 2004). The peak discharges of the 1897, 1909, 1917, and 1921 floods have the strongest influence on the magnitude of the 100-year flood discharge because they are the four largest discharges used in the flood-frequency analysis.”

On page 2—Second paragraph, last sentence rewritten as “Therefore, any inaccuracy in the peak discharge of the 1921 flood would affect accuracies of the peak discharges of the other three largest floods used in the flood-frequency analysis.”

Third paragraph, first sentence rewritten as “The slope-area measurement of the 1921 peak discharge was based on (1) three surveyed cross sections, along a reach of the river a short distance downstream of the Skagit River near Concrete streamflow-gaging station,…”

On page 14—Figure 10, upper right end of solid line on graph:

1921 “o” changed to “+”; 1898 date changed to 1897; “+” and 1917 date added below 1921 date.

On page 15—Second paragraph, first sentence rewritten as “The relative influence of various estimates of the peak discharge of the December 13, 1921, flood on the determination of the 100-year flood discharge for Skagit River near Concrete gaging station was evaluated by comparing the 100-year flood discharges determined from those estimates.

Remainder of second paragraph, “Annual peak discharges…streamflow data were not available.” was deleted.

Third paragraph, second sentence was rewritten as, “Peak discharges determined in this analysis for the 1921 flood ranged from 10.8 percent greater than…by Stewart.”

Third paragraph, third sentence was rewritten as, “Assuming that the same approximate range in percentage of differences would apply to the other three historic peak discharges, discharges 10 percent greater than and 10 percent less than those determined by Stewart were calculated (table 1).

Fourth paragraph, first sentence: The word “distribution” was replaced with “flood-frequency analysis.”

On page 16—Second paragraph, first sentence was rewritten as, “The four largest annual peak discharges used in the determination of the 100-year flood discharge at Skagit River near Concrete, Washington, occurred in 1897, 1909, 1917, and 1921.

Cover 4—Addition of “Version 2.0, August 2005” under report series and number.

Removed the U.S. Geological Survey 125^th anniversary logo