Estimating flood-peak discharge magnitudes and frequencies for rural streams in Illinois

[摘要] Flood-peak discharge magnitudes and frequencies at streamflow-gaging sites were developed with the annualmaximum series (AMS) and the partial duration series (PDS) in this study. Regional equations for both flood serieswere developed for estimating flood-peak discharge magnitudes at specified recurrence intervals of rural Illinoisstreams. The regional equations are techniques for estimating flood quantiles at ungaged sites or for improvingestimated flood quantiles at gaged sites with short records or unrepresentative data. Besides updating at-site floodfrequencyestimates using flood data up to water year 1999, this study updated the generalized skew coefficientsfor Illinois to be used with the Log-Pearson III probability distribution for analyzing the AMS, developed a programfor analyzing the partial duration series with the Generalized Pareto probability distribution, and applied theBASINSOFT program with digital datasets in soil, topography, land cover, and precipitation to develop a set of basincharacteristics. The multiple regression analysis was used to develop the regional equations with subsets of the basincharacteristics and the updated at-site flood frequencies. Seven hydrologic regions were delineated using physiographicand hydrologic characteristics of drainage basins of Illinois. The seven hydrologic regions were used forboth the AMS and PDS analyses.Examples are presented to illustrate the use of the AMS regional equations to estimate flood quantiles at anungaged site and to improve flood-quantile estimates at and near a gaged site. Flood-quantile estimates in fourregulated channel reaches of Illinois also are approximated by linear interpolation. Documentation of the flood datapreparation and evaluation, procedures for determining the flood quantiles, basin characteristics, generalized skewcoefficients, hydrologic region delineations, and the multiple regression analyses used to determine the regionalequations are presented in the main text and appendixes.

[发布机构] U.S. Geological Survey

[学科分类] 地球科学(综合)