Revision History for U.S. Geological Survey Scientific Investigations Report 2016–5050
By Thomas Over, Riki Saito, Andrea Veilleux, Jennifer Sharpe, David Soong, and
Audrey Ishii
Estimation of Peak Discharge Quantiles for Selected Annual Exceedance Probabilities in Northeastern Illinois
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Posted online June 28, 2016
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Revised and reposted November 27, 2017
The text version was modified.
The covers, title page, and the back of the title page were revised to show the new version number for SIR 2016-5050. Two graphs were removed from the front cover.
Subsequent to publication of SIR 2016–5050, an error was discovered in the reported methodology. It was discovered that the at-site flood frequencies computed using so-called “weighted” skew coefficient values were not actually computed using the weighted skew; that is, as a weighted average of the station and regional skew values. Instead, the flood frequencies were computed using the regional skew only.
The preferred skew coefficients to use for computing at-site flood frequencies are the weighted skews; however, it was determined that the flood frequencies obtained using the regional skew have only modest differences from those obtained using the weighted skews. As a result, it was decided to correct the report to reflect the methodology actually implemented. An update of the analysis and report are planned, which will use the weighted skew values and include additional years of record.
The following revisions to SIR 2016–5050 reflect what was actually done in the analysis and correct a few typographical and grammatical errors.
Corrections related to skewness coefficients:
On p. 1, in the second paragraph of the abstract, "...generalized skew coefficients..." was changed to "...regional skew coefficients..."
On p. 8, in the first paragraph in the left column, "...that is weighted with the at-streamgage skewness values in the frequency analysis...” was revised to read, "...for use in the frequency analysis..."
On p. 12, in the last sentence that begins in the left column, "The skewness estimate from this relation was combined with the at-site skew according to their associated uncertainties to obtain a weighted skew estimate for use in obtaining the at-site peak discharge quantile estimation..." was revised to read, "The regional skewness estimate from equation 3, without weighting with the at-site skewness, was used to obtain at-site peak discharge quantile estimates..."
On p. 12, in the last paragraph, including equation 4 and following "where" entries (now deleted), the entire paragraph was revised to read, "For use in the frequency analysis, the skewness values for each streamgage were taken as equal to the regional skewness values developed as described in the “Regional Skew Analysis” section and appendix 1."
On p. 22, in the first paragraph, "...including weighting with the regional skew model...” was revised to read, "...including application of the regional skew model..."
On p. 22, in the first "where" paragraph after equation 8 (formerly eq. 9), "...with weighted skew in cubic..." was revised to read, "...with regional skew in cubic..."
On p. 33, in the second "where" paragraph after equation 16 (formerly eq. 17), "...by using EMA with weighted skew as..." was revised to read, "...by using EMA with regional skew as..."
On p. 33, in the first paragraph after the "where" paragraphs after equation 16 (formerly eq. 17), '…in the rows labeled "EMA (weighted skew"), "Regional regression", and "Weighted EMA (weighted skew) and regional regression", respectively.' has been revised to read "…in the third, fourth, and fifth rows, respectively, for each streamgage."
On p. 39, in the left column, in the first complete paragraph, "To improve the skew estimates used for the peak discharge quantile estimation, weighted skew coefficients were computed as the variance-weighted average of at-site and generalized skew coefficients. The generalized skew coefficients..." was revised to read, "For the peak discharge quantile estimation, regional skew coefficients were used in place of the at-site skew. The regional skew coefficients..."
On various pages, equation numbers and references to equations 5 and larger have been reduced by 1 because of the deletion of equation 4.
Downloadable file of table 2, in the third of five rows for each streamgage, in the "Frequency analysis method" column, "At-site, adjusted for urbanization, EMA, weighted skew: (Qp)g,s" has been revised to read, "At-site, adjusted for urbanization, EMA, regional skew: (Qp)g,s"
Corrections of typographical and grammatical errors:
On title page and p. 1, middle initials were added with author names.
On p. x, water year definition was added.
On p. 2, first paragraph, "whereas for simulation models, regional calibration is a 'difficult, unsolved problem' (Vogel, 2006)." has been revised to read, "whereas significant challenges remain for regional calibration of simulation models (Vogel, 2006)."
On p. 2, second paragraph under "Description of Study Area" heading, "...vegetation type, primarily alfisols, which form under forest, nearer to Lake Michigan and mollisols, which form under grasslands, over..." has been revised to read, "...vegetation type. Alfisols, which form under forests, dominate nearer to Lake Michigan, whereas mollisols, which form under grasslands, cover..."
On p. 7, added a reference for the quote in the second paragraph.
On p. 8, in the x-axis for figure 4, "Fraction of basins" has been revised to read, "Urbanized fraction (Theobald, 2005, classes 7–10) of basin at end of record used in Soong and others (2004)."
On p. 8, in the y-axis for figure 4, "Empirical distribution function of fraction of Theobald (2005) classes 7-10 at end of the streamgage record" has been revised to read, "Fraction of basins having urbanized fraction less than value on x axis."
On p. 8, in the caption for figure 4, "...(from Soong and others, 2004)" has been revised to read, "...of Soong and others (2004)."
On p. 9, in the first line of text, "The list streamgages with at least 10 years of record..." has been revised to read, "The list of streamgages with at least 10 years of record..."
On p. 11, in the last line of the caption for figure 6, "greater than...” has been revised to read, “fewer than..."
On p. 14, added a reference for the National Inventory of Dams in the first full paragraph of the second column.
On p. 20, in the middle line of the caption for figure 10, "...urban fraction with least squares with quantile regression..." has been revised to read,"...urban fraction with quantile regression..."
On p. 47, table 1-3, fixed several values in the "Average regional skew" column
Throughout the report:
Corrected capitalization and formatting of text and headings, and the use of punctuation, where applicable.
Corrected some usage of abbreviations to ensure they were defined at first use and used thereafter (and redefined for every figure and table).
URLs were changed to "https," where applicable, and DOI URLs were changed from "http://dx.doi.org/..." to "https://doi.org/..."
Where necessary, changed singular verbs referring to "data" to plural verbs because "data" is the plural of "datum."
Corrected out-of-order figure callouts by adding callouts to sections in the report where the figures are located.
In parentheses, changed "equation" to "eq." and "figure" to "fig."
Downloadable file of table 2, column K in the group of columns with the header "Discharge for a given annual exceedance probability, ft3/s," the subheader "0.01" has been revised to read "0.005"
Downloadable file of table 13, changed "DEM_P_1_0" to "DEM_1_0_P"