HEC-WAT leverages unique plugins specific to HEC-WAT and existing software to work together through a plugin architecture. The plugin architecture allows externally developed stand alone software packages to integrate without requiring special code in HEC-WAT to support them. There are numerous ways to implement plugins for other software applications to participate in the HEC-WAT framework.

HEC-WAT is not aware of the individual pieces of software used; it simply loads a set of plugins and calls the API endpoints based on the context of the user's specifications through the model alternatives and the linkages of the model alternative inputs and outputs. The individual pieces of software provide the technical mechanics within the framework (e.g., editing, reporting capability, computational analyses, etc.) and are not intended to contain any code specific to HEC-WAT. Developers can follow the Plugin Developers Guide to develop their own plugins for HEC-WAT. The primary HEC applications have plugins and a few additional plugins specific to HEC-WAT are integrated in the HEC-WAT software install package.


HEC-WAT Framework - Basic Conceptual Diagram

The HEC-WAT software install package includes plugins for the following HEC software applications:

Hydrologic – HEC-HMS

HEC-HMS (http://www.hec.usace.army.mil/software/hec-hms/) is a standalone software application that is designed to simulate the precipitation-runoff processes of dendritic watershed systems. The software is designed to be applicable in a wide range of geographic areas and is a generalized hydrologic modeling system capable of representing many different watersheds to simulate either a single flood event or a continuous simulation that spans a couple of weeks or multiple decades. A model of the watershed is constructed by selected modeling methods for different components of the hydrologic cycle defining meteorologic boundary conditions. HEC-HMS in the HEC-WAT compute sequence is a hydrologic precipitation rainfall-runoff model that generally provides simulated flow at multiple locations within a watershed.

Reservoirs – HEC-ResSim

HEC-ResSim (http://www.hec.usace.army.mil/software/hec-ressim/) is a standalone software application that is used to model reservoir operations at one or more reservoirs whose rule-based operations are defined by a variety of operational goals and constraints. The software simulates reservoir operations for flood management, low flow augmentation and water supply for planning studies, detailed reservoir regulation plan investigations, and real-time decision support. HEC-ResSim in the HEC-WAT compute sequence is a reservoir simulation model that provides regulated flow hydrographs. Results from both HEC-HMS and HEC-ResSim can be used by the hydraulics model.

Hydraulics – HEC-RAS

HEC-RAS (http://www.hec.usace.army.mil/software/hec-ras/) is a standalone software application that allows the user to perform one- dimensional steady and unsteady flow and two-dimensional unsteady flow simulations. HEC-RAS also includes sediment transport/mobile bed computations and water temperature modeling. HEC-RAS contains four one-dimensional river analysis components for: (1) steady flow water surface profile computations; (2) unsteady flow simulation; (3) movable boundary sediment transport computations; and (4) water quality analysis. The HEC-RAS Mapper tool that is available from the HEC-RAS interface, calculates inundation boundary and water depth maps. HEC-RAS in the HEC-WAT compute sequence is a river hydraulic model that computes the river stages, water surface profiles, and levee breach information that is used to compute consequences by HEC-FIA.

Consequences – HEC-FIA

HEC-FIA (http://www.hec.usace.army.mil/software/hec-fia/) is a standalone software application that evaluates consequences using either continuously observed or simulated stage hydrographs (hydrograph-based) or depth grids (GIS-based). For a specified analysis, the software evaluates urban and agricultural flood damage, area inundated, number of structures inundated, and consequences. Consequences include economic and life loss. HEC-FIA also provides information to flood managers and emergency managers for emergency response activities.




HEC-WAT has multiple types of plugins that provide a variety of useful features. There are two main types of plugins that are important to note and discuss that pertain to the computation of results in HEC-WAT:

  • Computable plugins
  • Hydrologic Event Generator plugins

Computable plugins can participate in the program sequence within an HEC-WAT simulation, meaning that they can be linked to other models, compute results, and may produce output variables. All plugins that participate in the program sequence in a WAT compute are considered computable plugins.

Hydrologic Event Generator plugins are a specific subset of computable plugins. They support the FRA Compute type in HEC-WAT by providing the list of hydrologic events in an FRA simulation. 

The following computable plugins are provided with the installation package for HEC-WAT: 

Hydrologic Sampler

The Hydrologic Sampler plugin can generate system-wide hydrologic events for a Flood Risk Analysis compute, or Monte Carlo simulation. The outputs produced by the Hydrologic Sampler plugin can take the form of flow hydrographs or rainfall hyetographs spanning the analysis period selected for the simulation. This is a Hydrologic Event Generator plugin.

Stochastic Data Importer

The Stochastic Data Importer plugin is used to import user defined hydrologic data generated externally to HEC-WAT intended to be computed as events in an FRA compute, including both flow hydrographs and rainfall hyetographs. The Stochastic Data Importer plugin is only available for use during a Flood Risk Analysis compute. This is a Hydrologic Event Generator plugin.

Time Window Modifier

The Time Window Modifier plugin allows the user to change the time window computed by the Hydrologic Event Generator plugin (Hydrologic Sampler or Stochastic Data Importer). The time windows can be lengthened or shortened, and the Time Window Modifier  is typically used to shorten time windows to reduce computational burden for more complex models like HEC-RAS. The Time Window Modifier plugin is only available for use during a Flood Risk Analysis compute.

Time Window Interval Generator

The Time Window Interval Generator plugin can be used in a deterministic compute to break a multi-year continuous simulation into segments that are 1 year in duration.  This is useful to support continuous simulation in some plugins higher in the program order, and annual sub-timewindows for other plugins lower in the program order. The Time Window Interval Generator plugin is only available for use during a deterministic compute.

Scripting 

The Scripting plugin allows the user to write a Jython script to perform customized actions during the compute sequence.

Fragility Curve Sampler

The Fragility Curve Sampler plugin supports random selection of both the probability and trigger elevation of failures at levee breach locations identified as part of an HEC-RAS model alternative. The Fragility Curve Sampler plugin is only available for use during a Flood Risk Analysis compute.

Performance Metrics 

The Performance Metrics plugin generates the following performance and economic results:

  • Assurance
  • Annual Exceedance Probability
  • Long-Term Exceedance Probability
  • Expected Annual Damage

The Performance Metrics plugin is only available for use during a Flood Risk Analysis compute.