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.
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.
Error in Mean Elevation for HUC 02050302 Corrected 5/26/10
On 5/26/2010 an error was reported by a user regarding unreasonable flow estimates for watersheds delineated in Hydrologic Unit Code (HUC) 02050302, around Altoona, PA. Upon investigation, we determined that a conversion factor was incorrectly specified for the data in that HUC, and the program was reporting mean elevation values that were too high by a factor of 100. As a result, the peak flow estimates for watersheds delineated in this HUC were far too low. Mean annual streamflow estimates also were affected, and were too high. All other flow estimates were not affected. The problem was corrected on 5/26/2010. The erroneous data are believed to have been put in place 11/19/2009, to correct a problem that had caused incorrect delineations in the northeast portion of that HUC (the Juniata River), northeast of Huntingdon. Users may see the problem area indicated on the current Pennsylvania StreamStats web site. (Users may turn off the alert message polygon by unchecking the "DataProblemAlert" layer in the Map Contents panel.)
The USGS StreamStats team regrets the error, and is modifying our procedures to reduce the chance of similar errors in the future. Users are reminded, however, it is the user's responsibility to always check the results completely, and to use professional judgment. In this case the Ungaged Site Reports would have clearly indicated that the mean elevation value was outside the valid range for the regression equations. The reported elevations would have been unreasonable, for example 180,000 feet instead of 1800 feet. Users who have gotten such results should re-run the analysis on the StreamStats web site.
Users are requested to report any unusual or unreasonable results or other problems to the StreamStats team at GS-W StreamStats@usgs.gov.
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.
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