Jennifer B. Sharpe

Bathymetric survey of Rock Run Rookery Lake, Will County, Illinois.

The bathymetric data set was collected in Rock Run on Dec. 10, 2015 by USGS ILWSC staff Clayton Bosch and Louis Pappas. The bathymetric data were collected with an RD Instruments 1200 kHz ADCP (S/N 8617) and Trimble Ag 162 GPS mounted on the M/V La Moine. A temporary reference point (TRP) was established on the north side of the footbridge over the connecting channel to the Des Plaines River. The mean water surface elevation (504.97 feet, WGS 84) during the survey was established from a temporary reference point whose elevation was later established by GPS survey. The measured depths were then converted to a lake bed elevation. The location and depth data were compiled into a bathymetry dataset (Rock Run Bathymetry Data.csv). The dataset was imported as a shapefile into ArcMap (ArcGIS software 10.3.1). A shape file of lake boundary elevation was developed based on imagery from September 16, 2015 (U.S. Department of Agriculture Farm Services Agency National Agriculture Imagery Program (NAIP)) (point data can be found in Rock Run Lake Boundary.csv). This shape file was merged with the elevation shape file to enforced the lake and island edges in the final bathymetry. This elevation shape file was then contoured using Geostatistical Analyst/Deterministic methods/Radial Basis Functions with Completely Regularized Spline (defaults were used except Sector type: 4 Sectors, Angle: 42, Major semiaxis: 800, Minor semiaxis: 500). The raster was then exported to a GeoTIFF file with a resulting raster cell size of 1 foot.

Estimation of peak discharge quantiles for selected annual exceedance probabilities in northeastern Illinois

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.

Ohio River backwater flood-inundation maps for the Saline and Wabash Rivers in southern Illinois

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