United States Army Corps of Engineers (USACE) policy states that USACE will analyze water resources projects using a risk framework that incorporates watershed and systems approaches. USACE's Hydrologic Engineering Center (HEC) developed the Watershed Analysis Tool (HEC-WAT) to support these requirements.

In 2000 the National Research Council published a report reviewing how the Hydrologic Engineering Center's Flood Damage Assessment (HEC-FDA) software improved the state of the practice for water resources risk analysis. In that document, the authors described a series of improvements that they saw as necessary to further advance the state of the art and the state of the practice. Those recommendations were:

  • Support Systems Based Approaches
  • Separate Natural Variability and Knowledge Uncertainty
  • Evaluate Consequences at the Individual Structure Level
  • Utilize an Event-Based Monte Carlo Approach

Messrs. Christopher Dunn, Gary Brunner, Jeff Harris, William Charley, and John DeGeorge developed an initial design of HEC-WAT which was adapted by Mike Deering to include the Flood Risk Analysis (FRA) compute option in response to these recommendations.  Once a draft design document was created, the formal design process started and several other individuals joined the team: Mike Deering, Beth Faber, William Lehman, Mark Jensen, William Scharffenberg, Joan Klipsch, and Penni Baker. The above personnel were also involved in the development and implementation of the Flood Risk Analysis (Monte Carlo) compute option. Development and testing of the final release of Version 1.0 was led by Lea Adams, Chief, Water Resource Systems Division, and Version 1.1 was led by William Lehman, Economist, Water Resource Systems Division, Hydrologic Engineering Center.

HEC-WAT helps a study team perform the necessary hydrologic, hydraulic, environmental, and consequence analysis to support the planning function by integrating water resources software that is commonly applied by a multi-disciplinary study team when conducting a water resources study. Many pieces of software within the HEC suite of tools are implemented within HEC-WAT, thus allowing a study team to perform many of the necessary hydrologic, hydraulic, and consequence analyses from a single interface. The HEC software currently incorporated in HEC-WAT includes HEC-HMS (hydrology), HEC-ResSim (reservoir operations), HEC-RAS (hydraulics), and HEC-FIA (consequences).

The development of the Flood Risk Analysis (FRA) compute option within the HEC-WAT software allows a watershed or study area to be analyzed in a systems context using risk analysis and also supports risk-based analyses and risk-informed decision-making. FRA uses event-based Monte Carlo-style uncertainty sampling to evaluate the impact of natural variability and knowledge uncertainty across a watershed or within a system, which in turn provides a more complete picture of flood risk in a watershed.

The goal of HEC-WAT is to help USACE offices perform all types of water resource studies in a coordinated and comprehensive fashion. HEC-WAT accomplishes this goal through a plugin architecture that allows for integration of other software applications. These applications provide their own editors to the user through the HEC-WAT plugin API to facilitate editing and viewing through the HEC-WAT application. HEC-WAT facilitates computation of these models within the plugin API, including provision of random seeds within the Monte Carlo portion of the FRA compute option. This allows a seamless, repeatable, system-wide approach to watershed modeling. Through this framework the user can organize and develop alternatives and compare results.

Mark Ackerman, Ben Chacon, Ryan Ripken, John DeGeorge, and Shannon Newbold of Resource Management Associates (RMA) developed the graphical user interface, developed the concept of plugins, implemented and assisted HEC in the development of the plugins, and assisted with debugging and the overall design of the program.