v2.4 Release Notes

Beta released:

Final released:

New Features

Peaks Over Threshold Analysis

A Peaks Over Threshold analysis was added to HEC-SSP. The Peaks Over Threshold analsysis provides a streamlined approach to performing a peaks over threshold analysis on a variety of hydrologic and meteorologic data. The analysis allows users to extract a partial duration series using multiple filtering criteria.

Users can visualize diagnostic data that help inform selection of an appropriate threshold.

The analysis allows users to plot an event count histogram, annualized frequency curve, and confidence limits.

The Peaks Over Threshold analysis enables users to investigate the sensitivity of the results to annualization method, distribution fitting method, threshold value, and time separation and magnitude differential criteria. Flood and precipitation frequency analyses are typically performed using a block maxima approach/annual maximum series. Peaks over threshold analysis is likely a new concept to many HEC-SSP users. Additional information on the Peaks Over Threshold analysis can be found in the HEC-SSP User's Manual and in the Fall 2024 HEC Newsletter. 

Available Tutorials

User's Manual documentation on the Peaks Over Threshold Analysis is available here: Peaks Over Threshold Analysis User's Manual

A frequently asked questions (FAQ) page on peaks over threshold analysis is available here: Peaks Over Threshold Frequently Asked Questions

Tutorials illustrating usage of the Peaks Over Threshold analysis are available here: Peaks Over Threshold Tutorials

A 2-day Partial Duration Series workshop was taught in 2023, prior to the implementation of the Peaks Over Threshold analysis in HEC-SSP. Tutorials in this workshop utilize R.

Available Webinar

This feature was presented in a webinar.

This feature was funded by the U.S. Army Corps of Engineers (USACE) Headquarters General Investigations (GI) program and the Science and Engineering Technology (SET) program. Initial code implementation and documentation were completed by Avital Breverman, Mike Bartles, Nick Van, Will Lehman, and Greg Karlovits. Testing was completed by HEC staff (Avital Breverman, Mike Bartles, Greg Karlovits, and Melissa Mika), Philadelphia District (Elizabeth Shaloka), Louisville District (Matthew Fox), Rock Island District (Alex Morrison) and USGS staff (Nancy Barth, Sarah Murphy, and Nick Taylor).

Bugs Fixed

The following bugs were present in previous versions and have been fixed within version 2.4.

USGS Data Import

The U.S. Geological Survey is in the process of updating their data access tools and APIs to refer to Water Data for the Nation (WDFN). As such, the USGS download capabilities within HEC-SSP have undergone updates and modernization efforts. When downloading data directly from the USGS within HEC-SSP, you should notice that the importer now appends the USGS station ID in the F-part column of the station table and to data object names (e.g., USGS-01381500) for easier identification. This issue was fixed within v2.4-beta.1.

USGS Data Import: Location qualifier disambiguation

When importing USGS station data, location qualifiers such as "at", "nr" (near), "above", and "below" are now preserved in DSS record paths and data names. Previously, stations like "Whippany River at Morristown, NJ" and "Whippany River nr Morristown, NJ" could produce identical DSS paths, causing data collisions. The importer now appends the USGS station ID in the F-part column of the station table and to data object names (e.g., USGS-01381500) for easier identification. This issue was fixed within v2.4-beta.1.

Time series plot variable determination was case-sensitive

In previous versions, the dataset variable was case-sensitive. HEC-DSS C-parts of "FLOW" and "Flow" were not considered the same variable type and these time series were plotted on different y-axes. Variable type is now case-insensitive. This bug was introduced in v2.2 and fixed within v2.4-beta.1

Distribution Fitting Analysis confidence limits and expected probability curves

In previous versions, confidence limits and expected probability curves computed within the Distribution Fitting Analysis were truly random and not reproducible.  The computed confidence limits and expected probability curves for two analyses with the same dataset, distribution, and distribution fitting method were different.  Confidence limits and expected probability curves are now pseudo random and reproducible for a given dataset, distribution, and distribution fitting method combination. This bug was introduced in v2.2 and fixed within v2.4-beta.1.

Variable Time Window option doesn't include perception thresholds prior to start of systematic/historical data

In previous versions, when using the variable time window option within the Bulletin 17 analysis, perception thresholds that were entered prior to the start of the first systematic or historical event were not included in the analysis.  This issue has been rectified such that all data is incorporated when using the variable time window compute option.  This bug was introduced in v2.3 and fixed within v2.4-beta.1.

Selecting a Data Set prior to entering an Analysis Name causes an error when re-opening a study

Selecting a Data Set prior to entering a Name in the Bulletin 17, General Frequency, Volume Frequency, Balanced Hydrograph, Duration, or Distribution Fitting analyses caused an error when the study was re-opened. Users must now enter a Name prior to selecting a Data Set in these analysis types. This bug was introduced in v2.2 and fixed within v2.4-beta.1.

Correlation Analysis drops Name, Description, DSS File Name, and Report File fields after successful compute

In previous versions, the Correlation Analysis dropped user-entered information (Name, Description, DSS File Name, Report File, and location information) after a successful compute. This bug was introduced in v2.3 and fixed within v2.4-beta.1.

Incorporate zeroes in the sample size when checking manual censoring threshold

When using the Multiple Grubbs-Beck (MGB) test to examine and possibly censor low outliers in combination with Bulletin 17C procedures, no more than half of the exactly known observations (i.e., systematic data) can be censored. When manually defining the MGB censoring threshold, a check is performed to ensure that the user-defined threshold won't censor more than half of the exactly known observations. Within previous versions, this check was incorrectly disregarding zero values. This bug was introduced in v2.1 and fixed within v2.4-beta.1.

Coincident Frequency Analysis Manual Entry Duration Analysis variable name and units labels

Within the Coincident Frequency Analysis, the labels for Data Name and Data Variable were not displaying correctly when the Manual Entry method of specifying a frequency curve was selected. This bug was introduced in v2.3 and fixed in v2.4-beta.1.

Manual Entry Duration Analysis XML file name

In previous versions, the XML file name for a manual entry Duration Analysis was always Manual-Entry_Duration.xml. This caused issues when users attempted to select the analysis within an Coincident Frequency Analysis. The XML file associated with a manual entry Duration Analysis is now named based on the analysis name. This issue was introduced in v2.0 and fixed within v2.4-beta.1.

Manual Entry Duration Analysis exceedance probabilities

In previous versions, the computed exceedance probabilities used in a manual entry Duration Analysis were different than the exceedance probabilities displayed on the Options tab of the Duration Analysis Editor. As a result, when a manual entry Duration Analysis was computed, the computed curve would not align with the user-specified exceedance probabilities. This issue was introduced in v2.0 and fixed within v2.4-beta.1.

Volume Frequency Analysis Summary Report tables display quantiles in reverse order for low flow (annual minima)

When computing a low flow Volume Frequency Analysis (using annual minima), the Summary Report would display the compute quantiles in reverse order. The quantiles are now displayed in the correct order. This issue was introduced in v1.0 and fixed within v2.4-beta.1.

Graphical Frequency plotting positions for Median/Hazen

When computing plotting positions for graphical frequency in a General Frequency Analysis, the points would fail to plot if Median or Hazen is initially selected for the plotting positions. This bug was fixed within v2.4-beta.1.

Prevent erroneous Bulletin 17C confidence limits

When using a data set with very few annual peaks (e.g., 10) and regional skew information in the Bulletin 17 analysis, confidence limits could be erroneous for rare AEP. This bug was fixed within v2.4-beta.1.

Beta Releases

The following table presents features that were added and bugs that were fixed within each beta release.  Only bugs that were introduced and fixed during the v2.4 development cycle are listed here.