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Scientific Investigations Report 2009–5197

In cooperation with the Illinois Center for Transportation, Illinois Department of Transportation, and the Illinois Department of Natural Resources—Office of Water Resources

Implementation and Evaluation of the Streamflow Statistics (StreamStats) Web Application for Computing Basin Characteristics and Flood Peaks in Illinois

By Audrey L. Ishii, David T. Soong, and Jennifer B. Sharpe



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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 and others, 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 with streamflow-gaging station data; hydroprocessing the 30-meter digital elevation model (DEM) for Illinois to conform to streams represented in the National Hydrographic 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 a 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 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 after four mislocated sites were removed. A comparison of manual 100-year flood-quantile computations with ILSS at 34 sites indicated no statistically significant difference. ILSS appears to be an accurate, reliable, and effective tool for flood-quantile estimates.

First posted February 2010

For additional information contact:
Director, Illinois Water Science Center
U.S. Geological Survey
1201 West University Avenue, Suite 100
Urbana, IL 61801

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Suggested citation:

Ishii, A.L., Soong, D.T., and Sharpe, J.B., 2010, Implementation and evaluation of the Streamflow Statistics (StreamStats) Web application for computing basin characteristics and flood peaks in Illinois: U.S. Geological Survey Scientific Investigations Report 2009–5197, 25 p.

Also published as:
Ishii, A.L., Soong, D.T., and Sharpe, J.B., 2010, Implementation and evaluation of the Streamflow Statistics (StreamStats) Web application for computing basin characteristics and flood peaks in Illinois: Illinois Center for Transportation Report FHWA-ICT-10-063, 39 p.




Implementing Illinois StreamStats (ILSS)

Data Preparation

Computer Code Development

Illinois StreamStats Database

Evaluation and Adjustment of Basin Characteristics

Drainage Basin Area, Percent Water, Average Soil Permeability

Basin Length

Stream Slope

Evaluation of Flood-Peak Quantiles

Test of Illinois StreamStats Usage Consistency

Sensitivity of Flood-Peak Quantiles

Conclusions and Limitations



References Cited

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