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R27-181, National Transportation Library (NTL) Curation Note: As this dataset is preserved in a repository outside U.S. DOT control, as allowed by the U.S. DOT’s Public Access Plan (https://doi.org/10.21949/1503647) Section 7.4.2 Data, the NTL staff has performed NO additional curation actions on this dataset. The current level of dataset documentation is the responsibility of the dataset creator. NTL staff last accessed this dataset at its repository URL on 2023-12-12. If, in the future, you have trouble accessing this dataset at the host repository, please email NTLDataCurator@dot.gov describing your problem. NTL staff will do its best to assist you at that time., The U.S. Geological Survey Central Midwest Water Science Center completed a report (Over and others, 2023) documenting the methods, results, and applications of an updated flood-frequency study for the State of Illinois. This data release contains data related to the analysis completed to determine peak-flow quantiles (flood frequency estimates) at streamgages in Illinois for 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities (AEPs), as well as data used to develop regional regression equations that relate the peak-flow quantiles and the basin characteristics of selected streamgages in Illinois, Indiana, and Wisconsin, based on data through water year 2017 (a water year is the period from October 1 to September 30 and is designated by the year in which it ends; for example, water year 2017 was from October 1, 2016, to September 30, 2017). There is one set of equations for each of Illinois’ seven hydrologic regions, and, for each region, one equation for each AEP. These regional equations allow the estimation of peak-flow quantiles at ungaged locations throughout the state and their uncertainties. This data release contains a figure of the study area in addition to seven tables that provide both input data and results in tabular format. See metadata for detailed information., The total size of the zip file is 5.71 MB. The .csv, Comma Separated Value, file is a simple format that is designed for a database table and supported by many applications. The .csv file is often used for moving tabular data between two different computer programs, due to its open format. The most common software used to open .csv files are Microsoft Excel and RecordEditor, (for more information on .csv files and software, please visit https://www.file-extensions.org/csv-file-extension). The .jpg file extension is associated with JPEG (Joint Photographic Experts Group) file format. JPEG is a lossy image compression algorithm that significantly reduces the file size of the original image at the cost of quality. The higher the compression ratio the lower the quality of the .jpg file (for more information on .jpg files and software, please visit https://www.file-extensions.org/jpg-file-extension). The .xml file type is commonly used for files written in Extensible Markup Language (XML). XML is a human-readable, machine-understandable, general syntax for describing hierarchical data, applicable to a wide range of applications (for more information on .xml files and software, please visit https://www.file-extensions.org/xml-file-extension)

R27-181, National Transportation Library (NTL) Curation Note: As this dataset is preserved in a repository outside U.S. DOT control, as allowed by the U.S. DOT’s Public Access Plan (https://doi.org/10.21949/1503647) Section 7.4.2 Data, the NTL staff has performed NO additional curation actions on this dataset. The current level of dataset documentation is the responsibility of the dataset creator. NTL staff last accessed this dataset at its repository URL on 2023-12-12. If, in the future, you have trouble accessing this dataset at the host repository, please email NTLDataCurator@dot.gov describing your problem. NTL staff will do its best to assist you at that time., The U.S. Geological Survey (USGS) Central Midwest Water Science Center (CMWSC) completed a report (Over and others, 2023) documenting methods for peak-flow frequency analysis in Illinois following Bulletin 17C guidelines. The methods are used to provide estimates of peak-flow quantiles for 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities (AEPs) for selected USGS streamgages. This data release presents peak-flow frequency analyses for selected streamgages in Illinois, Indiana, and Wisconsin, based on data through water year 2017 (a water year is the period from October 1 to September 30 and is designated by the year in which it ends; for example, water year 2017 was from October 1, 2016, to September 30, 2017)., The total size of the zip file is 1.24 MB. The .csv, Comma Separated Value, file is a simple format that is designed for a database table and supported by many applications. The .csv file is often used for moving tabular data between two different computer programs, due to its open format. The most common software used to open .csv files are Microsoft Excel and RecordEditor, (for more information on .csv files and software, please visit https://www.file-extensions.org/csv-file-extension). The .xml file type is commonly used for files written in Extensible Markup Language (XML). XML is a human-readable, machine-understandable, general syntax for describing hierarchical data, applicable to a wide range of applications (for more information on .xml files and software, please visit https://www.file-extensions.org/xml-file-extension). The .txt file type is a common text file, which can be opened with a basic text editor. The most common software used to open .txt files are Microsoft Windows Notepad, Sublime Text, Atom, and TextEdit (for more information on .txt files and software, please visit https://www.file-extensions.org/txt-file-extension). The .psf file type is a common file type, but it mostly associated with the software Microstation by architects, engineers, contractors and GIS professionals (for more information on .psf files and software, please visit https://www.file-extensions.org/psf-file-extension-microstation-plot-specification-file). The .prt file extension is typically part of a larger CAD project and contains 3D information. This can be used by many CAD programs, but the file is not interchangeable (form more information on .prt files and software, please visit https://www.file-extensions.org/prt-file-extension). The .exp file type is created by several programs. It can be created by Microsoft Visual C++ to store exported data from C++ projects. It can also be created by CATIA CAD software to export data (for more information on .exp files and software

R27-181, This report presents the methods, results, and applications of an updated flood-frequency study for the State of Illinois. This study, which uses data through September 2017, updates two previous studies that used data through 1999 and 2009, respectively. Flood-frequency estimates are used for a variety of land-use planning and infrastructure design purposes, including for the hydraulic design of bridges. The flood frequencies presented are the stream discharges (or quantiles) that are exceeded each year with a given probability, called the annual exceedance probability (AEP). Estimates are provided for eight AEPs: 0.5, 0.2, 0.1, 0.04, 0.02, 0.01, 0.005, and 0.002. The basic data used are the annual maximum discharges (peak flows) at stream gages in and near Illinois and the measurable physical properties (basin characteristics) of the basins upstream from those stream gages. The logarithms of the peak-flow records at qualifying stream gages were fit to the Pearson Type 3 distribution using federally recommended methods, providing one of the two primary products of the study, which is the set of peak-flow quantiles at the stream gages and their uncertainties. The other primary product is sets of equations, determined by least-squares regression, that relate the peak-flow quantiles and the basin characteristics. There is one set of equations for each of Illinois’ seven hydrologic regions, and, for each region, one equation for each AEP. These regional equations allow the estimation of peak-flow quantiles at ungaged locations throughout the state and their uncertainties. A set of illustrative example applications is provided, and tables of all results at all study stream gages and regions are provided in associated data releases. The study results are also being made available in a web application, StreamStats.

R27-144, This report provides two sets of equations for estimating peak discharge quantiles at annual exceedance probabilities (AEPs) of 0.50, 0.20, 0.10, 0.04, 0.02, 0.01, 0.005, and 0.002 (recurrence intervals of 2, 5, 10, 25, 50, 100, 200, and 500 years, respectively) for watersheds in Illinois based, on annual maximum peak discharge data from 117 watersheds in and near northeastern Illinois. One set of equations was developed through a, temporal analysis with a two-step least squares-quantile regression technique that measures the average effect of changes in the urbanization, of the watersheds used in the study. The resulting equations can be used to adjust rural peak discharge quantiles for the effect of urbanization, and in this study the equations also were used to adjust the annual maximum peak discharges from the study watersheds to 2010 urbanization, conditions., The other set of equations was developed by a spatial analysis. This analysis used generalized least-squares regression to fit the peak discharge, quantiles computed from the urbanization-adjusted annual maximum peak discharges from the study watersheds to drainage-basin, characteristics. The peak discharge quantiles were computed by using the Expected Moments Algorithm following the removal of potentially, influential low floods defined by a multiple Grubbs-Beck test. To improve the quantile estimates, generalized skew coefficients were obtained, from a newly developed regional skew model in which the skew increases with the urbanized land use fraction. The drainage-basin, characteristics used as explanatory variables in the spatial analysis include drainage area, the fraction of developed land, the fraction of land, with poorly drained soils or likely water, and the basin slope estimated as the ratio of the basin relief to basin perimeter., This report also provides: (1) examples to illustrate the use of the spatial and urbanization-adjustment equations for estimating peak discharge, quantiles at ungaged sites and to improve flood-quantile estimates at and near a gaged site; (2) the urbanization-adjusted annual maximum, peak discharges and peak discharge quantile estimates at streamgages from 181 watersheds including the 117 study watersheds and 64, additional watersheds in the study region that were originally considered for use in the study but later deemed to be redundant., The urbanization-adjustment equations, spatial regression equations, and peak discharge quantile estimates developed in this study will be, made available in the web-based application StreamStats, which provides automated regression-equation solutions for user-selected stream, locations. Figures and tables comparing the observed and urbanization-adjusted peak discharge records by streamgage are provided at, http://dx.doi.org/10.3133/sir20165050 for download.