The following is one of over 75 programs & documentation included with Hydro-CD by Dodson

SWSTAT - Surface-Water Statistics 

VERSION/DATE: Version 4.1 - 02/25/2002




SWSTAT contains a number of options for statistically analyzing time-series data. The time-series data are read from a Watershed Data Management (WDM) file. The computed statistics and (or) time series can be written back to the WDM file or to a text file. The statistics options include:

Basic Computes minimum, maximum, mean, and standard deviation of a time series (any time step). Compare Uses flow-duration analysis and class intervals to compute absolute error, root mean square error, and bias by class interval for two time series. The standard error of estimate is computed. The flow-durations curves can be plotted. Data may be any time step.

Duration Performs traditional flow-duration analysis by counting occurrences of all time-series values within flow intervals. The duration curve can be plotted. Data are analyzed at a daily time step.

Frequency Analyzes time series using log-Pearson Type III distribution, without the extra features of Bulletin 17B found in the PEAKFQ program. The distribution is fitted by method of moments. Based on the USGS A193 WATSTORE program. Data are read from time-series data sets and analyzed at an annual time step.

Hydrograph Computes duration hydrograph tables and curves. Based on the USGS K956 WATSTORE program. The duration hydrograph curves may be plotted. Data are analyzed at a daily time step. Although originally developed for streamflow data, any time series may be analyzed.

N-day Computes annual n-day high and (or) low flows from a daily time series. A default set of 1-, 2-, 3-, 7-, 10-, 30-, 60-, 90-, 183-, and 365-day periods can be selected, or up to 10 durations may be specified. Analysis may be over a calendar year, water year, or a season. Based on the USGS A969 WATSTORE program.

Trend Tests annual time series for trends. Computes Kendall's tau, the associated p-level and the slope of the trend line. The p-level is the attained (two-sided) significance level of the test. The data may be read from a time-series data set or from a table data set.


Standard textbook procedures are used. The log-Pearson Type III and Pearson Type III distributions are fit using the method of moments. The Kendall Tau procedure is used for trend analysis. Class intervals used for flow-duration and comparison analysis are created as uniform log units or are user defined.


To install and run SWSTAT, the following are necessary:

- Pentium-class PC
- Windows 9x/Me, Windows NT 4.0, or Windows 2000
- up to 4.9 megabytes of free disk space
- 4.1 megabytes of free memory 



2012 - Walter P. Moore & Associates, Inc. - Houston, TX, USA