HEC-SSP is designed to perform statistical analyses of hydrologic data.  The following is a description of the major capabilities of HEC-SSP.  The following is a description of the major capabilities of HEC-SSP:

• User Interface
• Statistical Analysis Components
• Data Storage and Management
• Graphical and Tabular Output

User Interface

The user interacts with HEC-SSP through a graphical user interface (GUI).  The main focus in the design of the interface was to make it easy to use the software, while still maintaining a high level of efficiency for the user.  The interface provides for the following functions:

• File management

• Data entry, importing, and editing

• Statistical analyses

• Tabulation and graphical displays of results

• Reporting facilities

• Online help

Statistical Analysis Components

Flow Frequency Analysis (Bulletin 17B) – This component of the software allows the user to perform annual peak flow frequency analyses.  The software follows Bulletin 17B, “Guidelines for Determining Flood Flow Frequency,” by the Interagency Advisory Committee on Water Data.

Data Storage and Management

Data storage is accomplished through the use of "text" files (ASCII and XML), as well as the HEC Data Storage System (HEC-DSS).  User input data are stored in flat files under separate categories of study, analyses, and a data storage list.  Annual peak flows are stored in a project HEC-DSS file as time series data.  Output data is predominantly stored in HEC-DSS, while a summary of the results is written to an XML file.  Additionally, an analysis report file is generated whenever a computation is made.  This report file is written to a standard ASCII text file.

Data management is accomplished through the user interface.  The modeler is requested to enter a Name and Description for each study being developed.  Once the study name is entered, a directory with that name is created, as well as a study file.  Additionally a set of subdirectories is created with the following names: Bulletin17bResults; Layouts; and Maps.  As the user creates new analyses, an analyses file is created in the main project directory.  The interface provides for renaming and deletion of files on a study-by-study basis.

Graphical and Tabular Output

Graphics include a map window and frequency curve plots.  The map window can be used to display background map layers.  Locations of the data being analyzed can be displayed on top of the map layers.  The frequency curve plot shows the results of the 17B analysis, including: the analytically computed curve; the expected probability curve; confidence limits; and the raw data points plotted based on one of three available plotting position methods.  Tabular output consists of tables showing the computed frequency curves, confidence limits, and summary statistics.  All graphical and tabular output can be displayed on the screen, sent directly to a printer (or plotter), or passed through the Windows Clipboard to other software, such as a word-processor or spreadsheet.

A report file is available for each Bulletin 17B analysis.  This report file includes the input data; preliminary results; all of the statistical tests (Low and High Outliers; Broken Record; Zero Flows Years; Incomplete Record; Regional Skews; and Historic Information); and final results.  This report file is similar to the FFA output file.