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Title:Implementation and evaluation of the Streamflow Statistics (StreamStats) web application for computing basin characteristics and flood peaks in Illinois
Author(s):Ishii, Audrey L.; Soong, David T.; Sharpe, Jennifer B.
Subject(s):Flood frequency,flood-peak estimation, flood-peak discharge, streamflow statistics, automated watershed delineation, basin characteristics, Web application, StreamStats
Abstract:Illinois StreamStats (ILSS) is a Web-based application for computing selected basin characteristics and flood-peak quantiles based on the most recently (2010) published (Soong et al., 2004) regional flood-frequency equations at any rural stream location in Illinois. Limited streamflow statistics including general statistics, flow durations, and base flows also are available for U.S. Geological Survey (USGS) streamflow-gaging stations. ILSS can be accessed on the Web at by selecting the State Applications hyperlink and choosing Illinois from the pull-down menu. ILSS was implemented for Illinois by obtaining and projecting ancillary geographic information system (GIS) coverages; populating the StreamStats database (StreamStatsDB) with streamflow-gaging station data; processing the 30-meter digital elevation model (DEM) for Illinois to conform to streams represented in the National Hydrography Dataset 1:100,000 stream coverage; and customizing the Web-based Extensible Markup Language (XML) programs for computing basin characteristics for Illinois. The basin characteristics computed by ILSS then were compared to the basin characteristics used in the published study, and adjustments were applied to the XML algorithms for slope and basin length. Testing of ILSS was accomplished by comparing flood quantiles computed by ILSS at an approximately random sample of 170 streamflow-gaging stations computed by ILSS with the published flood-quantile estimates. Differences between the log-transformed flood quantiles were not statistically significant at the 95-percent confidence level for the State as a whole, nor by the regions determined by each equation, except for region 1, in the northwest corner of the State. In region 1, the average difference in flood-quantile estimates ranged from 3.76 percent for the 2-year flood quantile to 4.27 percent for the 500-year flood quantile. The total number of stations tested in region 1 was small (21) and the mean difference is not large (less than one-tenth of the average prediction error for the regression-equation estimates). The sensitivity of the flood-quantile estimates to differences in the computed basin characteristics are determined and presented in tables. A test of usage consistency was conducted by having at least 7 new users compute flood-quantile estimates at 27 locations. The average maximum deviation of the estimate from the mode value at each site was 1.31 percent for the 100-year flood quantile after four mislocated sites were removed. A comparison of manual 100-year flood-quantile computations with ILSS computations at 34 sites indicated no statistically significant difference. ILSS appears to be an accurate, reliable, and effective tool for flood-quantile estimates.
Issue Date:2010-01
Series/Report:ICT-10-063 UILU-ENG-2010-2003
Genre:Technical Report
Publication Status:published or submitted for publication
Peer Reviewed:not peer reviewed
Sponsor:Illinois Department of Transportation
Rights Information:No restrictions. This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161
Date Available in IDEALS:2013-11-05

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