Columbia River Treaty 2014/2024: HEC-WAT Innovations for CRT Computes

Abstract

In order for a 50,000 event flood risk analysis (FRA) computation to be feasible given the number and complexity of models in the Columbia River Treaty (CRT) 2014/2024 Review compute sequence, features and tools were added and enhanced in the HEC-WAT (Hydrologic Engineering Center's (HEC) Watershed Analysis Tool) software. The features were designed to speed up the simulation compute time as well as ensure that only the appropriate output was saved. Two features are responsible for reducing the simulation time, the Time Window Modification tool and the Skip Flag tool. The Time Window Modification tool provides capabilities for dynamically modifying the time window used by each model in the compute sequence; so that models did not have to use the same simulation time window. An added benefit of the Time Window Modification tool is the ability to find a starting time that meets boundary conditions and at the same time does not cause initial boundary conditions to go unstable. The Skip Flag tool provides an interface for defining thresholds (flow, stage, or other output) that are used to determine when certain models in the compute sequence are skipped. The amount of model files and data generated from a simulation of 50,000 events for the full CRT model could easily overwhelm a computer's storage. Features were added to remove model files at the end of a number of events while providing the flexibility to save specific files by defining the file name or file extension. Output data from the individual models can also be saved or deleted and an option was included to extract scalar values, like the maximum flow, from the individual models. For example, in order to compare CRT modeling alternatives, peak flows from the snowmelt season were evaluated. HEC-WAT was able to extract this maximum flow from output and discard the flow hydrograph for the entire water year.