Over, T.M., Saito, R.J., Veilleux, A.G., Sharpe, J.B., Soong, D.T., and Ishii, A.L., 2017, Estimation of peak discharge quantiles for selected annual exceedance probabilities in northeastern Illinois (ver. 2.0, November 2017): U.S. Geological Survey Scientific Investigations Report 2016–5050, 50 p. with appendix, https://doi.org/10.3133/sir20165050.

Subsequent to publication of the initial Illinois urban peak-flow regression report, SIR 2016–5050 version 1 in June, 2016, an error was found 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 from using the regional skew alone have only modest differences from those obtained using the weighted skews. As a result, it was decided to correct the report on an interim basis, creating SIR 2016–5050 version 2, to reflect the methodology actually implemented. The revised report was released on November 28, 2017, at https://doi.org/10.3133/sir20165050.

An update of the analysis and report are planned for October, 2018, which will use the weighted skew values and include additional years of record.