**StreamStats in Kentucky**

Kentucky StreamStats incorporates regression equations for estimating instantaneous peak flows with annual exceedance probabilities of 50, 20, 10, 4, 2, 1, 0.5, and 0.2 percent. These peak flows have recurrence intervals of 2, 5, 10, 25, 50, 100, 200, and 500 years, respectively. Equations for estimating mean annual flows, harmonic mean flows, and the 7-day 2-, 10-, and 20-year and 30-day 2- and 5-year low flows also are included. In addition, Kentucky StreamStats include equations for estimating bankfull flow, area, width, and depth. The reports below document the regression equations available in StreamStats for Kentucky, the methods used to develop the equations and to measure the basin characteristics used in the equations, and the errors associated with the estimates obtained from the equations. Users should familiarize themselves with these reports before using StreamStats to obtain estimates of streamflow statistics for ungaged sites.

- Brockman, R. A., Agouridis, C. T., Workman, S. R., Ormsbee, L. E., Fogle, A. W., 2012, Bankfull regional curves for the Inner and Outer Bluegrass Regions of Kentucky, Journal of the American Water Resources Association, v. 48, no. 2, p. 391-406.
- Hodgkins, G.A. and Martin, G,R., 2003, Estimating the Magnitude of Peak Flows for Streams in Kentucky for Selected Recurrence Intervals, U.S. Geological Survey Water-Resources Investigations Report 03-4180, 68 p., 1 plate.
- Martin, G.R., 2002, Estimating Mean Annual Streamflow of Rural Streams in Kentucky: U.S. Geological Survey Water-Resources Investigations Report 02-4206, 35 p.
- Martin, G.R., and Arihood, L.D., 2010, Methods for estimating selected low-flow frequency statistics for unregulated streams in Kentucky: U.S. Geological Survey Scientific Investigations Report 2010-5217, 83 p.
- Martin, G. R. and Ruhl, K. J., 1993, Regionalization of harmonic-mean streamflows in Kentucky: U.S. Geological Survey Water-Resources Investigations Report 92-4173, 47 p., 1 pl.

**Click on this link**** **to obtain general information on the Kentucky application, as well as specific sources and computation methods for basin characteristics.** **

## Availability of peak-flow estimates

The peak-flow regression equations are implemented only for hydrologic regions 2, 3, 5, 6, and 7 in Kentucky. Drainage area is the only explanatory variable in these equations. Equations for hydrologic regions 1 and 4 are not implemented at this time because an additional explanatory variable, stream slope, is needed to solve the equations. The capability for StreamStats to compute stream slope in a manner that duplicates the method used in the report by Hodgkins and Martin (2003) has not yet been devised.

## Probability of zero-flow estimates

The equations in Kentucky StreamStats for estimating the 7-day 2-, 10-, and 20-year and 30-day 2- and 5-year low flows (Martin and Arihood, 2010) were developed using logarithmic transformations of the variables, and thus they are unable to estimate zero flow. Consequently, the authors also developed equations for estimating the probabilities of zero flow occurring at the times of the 7-day 2-, 10-, and 20-year and 30-day 2- and 5-year low flows. These two sets of equations should be used in tandem. If the probability of zero flow is larger than the inverse of the return period, then the statistic is estimated to be zero. Alternatively, if the probability of zero flow is equal to or less than the inverse of the return period, then the estimated value of the low-flow statistic should be used. For example, if the PROBZ7Q20 statistic is larger than the inverse of the return period (1/20 or 0.05), then the value of M7D20 is estimated to be zero. If the PROBZ7Q20 statistic is less than or equal to 0.05, then the regression equation should be used to determine the value of M7D20.

StreamStats for Kentucky was developed in cooperation with the Kentucky Energy and Environment Cabinet, Department of Environmental Protection, Division of Water.