**StreamStats in Pennsylvania**

Pennsylvania StreamStats incorporates regression equations for estimating numerous streamflow statistics. Equations are included for estimating the 2-, 5-, 10-, 50-, 100-, and 500-year recurrence interval floods, which have the probability of exceedance in any single year of 50, 20, 10, 2, 1, and 0.2 percent, respectively. Equations also are included for estimating the 7-day, 10-year; 7-day, 2-year; 30-day, 10-year; 30-day, 2-year; and the 90-day, 10-year low flows, the 10-year, 25-year, and 50-year base flows, and the harmonic mean flow, and the mean annual flow. The reports below document the regression equations available in StreamStats for Pennsylvania, the methods used to develop the equations and to measure the basin characteristics used in the equations, references to GIS data layers used in the analysis, and the errors associated with the estimates obtained from the equations. Users should familiarize themselves with this report before using StreamStats to obtain estimates of streamflow statistics for ungaged sites.

- Roland, M.A., and Stuckey, M.H., 2008, Regression equations for estimating flood flows at selected recurrence intervals for ungaged streams in Pennsylvania: U.S. Geological Survey Scientific Investigations Report 2008-5102, 57 p.
- Stuckey, M.H., 2006, Low-flow, base-flow, and mean-flow regression equations for Pennsylvania streams: U.S. Geological Survey Scientific Investigations Report 2006-5130, 84 p.

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

In addition to solving the above regression equations, Pennsylvania StreamStats can be used to delineate drainage areas and to provide the basin characteristics that are needed as input for the **Ba**seline **S**treamflow **E**stimator (BASE) program, which can estimate daily mean streamflows for 1960-2008 for user-selected sites on ungaged streams. The estimates provided by BASE assume that flows at the selected site are minimally altered by human activities. Additional information on the BASE program, including instructions for downloading, installing, and operating the program are at the following web page:

**Note:** An adjustment factor is applied to the basin characteristic *mean basin slope* to more accurately replicate the values used to develop the regression equations. *Mean basin slope* is used in the regression equation for low-flow region 1. Both the raw (unadjusted) and adjusted basin slope values can be displayed using the BasinChars tool, however, only the adjusted value is displayed on the FlowStats form if the ungaged site of interest is within low-flow region 1.

StreamStats for Pennsylvania was developed in cooperation with the Pennsylvania Department of Protection, the Federal Emergency Management Agency, the Pennsylvania State Association of Township Supervisors, and the Susquehanna River Basin Commission.