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Scientific Investigations Report 2012–5168

Prepared in cooperation with the Kentucky Division of Water

Construction of Estimated Flow- and Load-Duration Curves for Kentucky Using the Water Availability Tool for Environmental Resources (WATER)

By Michael D. Unthank, Jeremy K. Newson, Tanja N. Williamson, and Hugh L. Nelson

Thumbnail of and link to report PDF (6.08 MB)Abstract

Flow- and load-duration curves were constructed from the model outputs of the U.S. Geological Survey’s Water Availability Tool for Environmental Resources (WATER) application for streams in Kentucky. The WATER application was designed to access multiple geospatial datasets to generate more than 60 years of statistically based streamflow data for Kentucky. The WATER application enables a user to graphically select a site on a stream and generate an estimated hydrograph and flow-duration curve for the watershed upstream of that point. The flow-duration curves are constructed by calculating the exceedance probability of the modeled daily streamflows. User-defined water-quality criteria and (or) sampling results can be loaded into the WATER application to construct load-duration curves that are based on the modeled streamflow results.

Estimates of flow and streamflow statistics were derived from TOPographically Based Hydrological MODEL (TOPMODEL) simulations in the WATER application. A modified TOPMODEL code, SDP-TOPMODEL (Sinkhole Drainage Process-TOPMODEL) was used to simulate daily mean discharges over the period of record for 5 karst and 5 non-karst watersheds in Kentucky in order to verify the calibrated model. A statistical evaluation of the model’s verification simulations show that calibration criteria, established by previous WATER application reports, were met thus insuring the model’s ability to provide acceptably accurate estimates of discharge at gaged and ungaged sites throughout Kentucky.

Flow-duration curves are constructed in the WATER application by calculating the exceedence probability of the modeled daily flow values. The flow-duration intervals are expressed as a percentage, with zero corresponding to the highest stream discharge in the streamflow record. Load-duration curves are constructed by applying the loading equation (Load = Flow*Water-quality criterion) at each flow interval.

First posted November 9, 2012

For additional information contact:
Kentucky Water Science Center
U.S. Geological Survey
9818 Bluegrass Parkway
Louisville, KY 40299-1906

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Suggested citation:

Unthank, M.D., Newson, J.K., Williamson, T.N., and Nelson, H.L., 2012, Construction of estimated flow- and load-duration curves for Kentucky using the Water Availability Tool for Environmental Resources (WATER): U.S. Geological Survey Scientific Investigations Report 2012–5168, 14 p., available only at




Model Description

Model Calibration and Verification

Construction of Estimated Flow-Duration Curves Using WATER

Construction of Estimated Load-Duration Curves Using WATER


References Cited

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