The U.S. Army Corps of Engineers (USACE) conducts water resources planning and management studies to fulfill USACE's Civil Works mission. These studies begin with the definition of problems, opportunities, objectives, and constraints and continue through the planning process by formulating, evaluating, and comparing alternatives. Various analyses are necessary to determine alternative performance and related impacts so that appropriate decisions may be made. The studies often require hydrologic/hydraulic, economic, environmental, and social performance and impact analyses. 

The Hydrologic Engineering Center (HEC) developed HEC-WAT to support field users in performing water resources studies in a comprehensive, systems-based approach. HEC-WAT leverages the typical HEC tools utilized by field users to evaluate project performance across a range of structural and nonstructural measures.

Flood Risk Management

USACE flood risk management (FRM) policy requires that USACE analytical processes must be consistent with applicable regulations and policies. The following documents provide a background of the policies that impact how water resources decisions are made using risk-informed decision making processes:   

From within USACE there is very little guidance and few tools to support these requirements. HEC-WAT seeks to provide a flexible framework that can meet the technical challenges for small and large watersheds. It includes an option that analyzes complex riverine systems across the range of natural variabilities while incorporating appropriate knowledge uncertainties. 

HEC-WAT Mission, Vision, and Goals

The HEC-WAT team seeks to provide a platform to integrate water resources. One way we do that is by providing software to facilitate the practice of "Integrated Water Resources Management” in support of the USACE Campaign Plan's Strategic Goal 2: Deliver Integrated Water Resource Solutions. The HEC-WAT Mission, Vision, and Goals align to produce a tool that can meet the needs of USACE across multiple business lines, provide useful decision metrics for many stakeholders, and support multi-disciplinary teams working in the field of Flood Risk Management. 

Mission

To provide a water resources tool that integrates engineering and consequence software to support a wide range of applications, including watershed and systems-based risk analysis.

Vision

Develop the primary integration tool for engineering and water resources studies.

Goals

  • To provide an excellent user experience
  • To provide innovative solutions to complex problems
  • To provide world class training and documentation
  • To support field applications of HEC-WAT for real world problems
  • To increase the combined capabilities of water resources engineering software

HEC-WAT Overview

HEC-WAT is software that orchestrates the building, editing, and running of a series of models to help perform water resources studies while addressing the USACE guidance described above. The software provides flexibility in the risk analysis phase of water resources studies. It can be used to perform small Continuing Authorities Program (CAP) studies or large comprehensive studies. The HEC-WAT interface streamlines and integrates the analytical process of water resource studies by using the software tools commonly applied by multi-disciplinary teams such as HEC-HMS (Hydrometeorology), HEC-ResSim (Reservoir Systems Analysis), HEC-RAS (Hydraulics), and HEC-FIA (Flood Consequences). 

The individual model applications used within the HEC-WAT framework can be built and edited inside or outside HEC-WAT, and model results can be viewed from HEC-WAT by selecting elements found on the schematic. Once the models are located (i.e., importing models, building models) within an HEC-WAT study, the models can be connected and run in a user-defined sequence. The models, the input data, and the results are all stored in HEC-WAT's directory structure. Therefore, all data and files used to make decisions are easily retrieved. Alternative analyses can be performed, and output from multiple alternatives can be viewed concurrently, making alternative analyses and alternative selection more efficient.

Supporting the USACE Planning Process

The USACE Planning Process is a well-defined six-step approach to problem-solving (ER 1105-2-100, Section 2-3).  This six-step process, applied in all USACE Planning projects, consists of the following steps:  

  • Step 1 - Identification of problems and opportunities
  • Step 2 - Inventory and forecasting
  • Step 3 - Alternative formulation
  • Step 4 -  Alternative evaluation
  • Step 5 - Alternative comparison
  • Step 6 - Plan selection

HEC-WAT assists project teams in the performance of Steps 2-5 of the Planning Process. 

In Step 2, a current or baseline condition as well as forecasted conditions are determined. The inventorying process involves defining the project or watershed boundaries, identifying existing data or models, and identifying what further products need to be developed to address the identified problems and opportunities. HEC-WAT facilitates identification of the geospatial scope of a project, what processes are included in the analysis, and how those processes work together. The hydrologic, hydraulic, reservoir operation, and consequence models identified in this step can all be placed and connected in the HEC-WAT framework, and the current and forecasted conditions can likewise be incorporated.

 In Step 3, alternative plans for the project are formulated by combining different alternative measures. Those alternatives can be represented in the HEC-WAT framework via the setup of the sub-models, which incorporate the various alternative measures. For example, alternative measures can can include structural measures such as levees (incorporated in HEC-RAS), reservoirs (incorporated in HEC-ResSim), detention basins (through HEC-HMS or HEC-ResSim), or a variety of other structural measures in the appropriate models. Nonstructural measures can be represented through HEC-FIA by elevating or removing structures from the inventory, changing warning scenarios, or flood proofing by changing depth-damage relationships. Alternatives are also used to represent future (forecasted) conditions, such as a reduction in permeable surfaces in HEC-HMS to show the impacts of future development. 

HEC-WAT supports evaluation of the alternatives (Step 4) through both the deterministic and Flood Risk Analysis (FRA) compute options. Once the alternatives have been evaluated, HEC-WAT provides the ability to generate and visualize results from the various component models. This facilitates comparison of the alternatives as part of Step 5 in the Planning Process.