The Hydrologic Modeling System (HEC-HMS): Toward a Complete Framework for Hydrologic Engineering

The Hydrologic Modeling System (HEC-HMS) is designed to perform deterministic hydrologic simulation in support of engineering studies. It is intended to assist in planning, designing, and operating projects by providing information about current and future runoff from watersheds, with and without water control structures. It is the integration of models for simulating the hydrologic cycle with models for simulating the operation of reservoirs, levees, diversions and other structures that make the program useful. Until recently, the program lacked the capability to address some types of studies. Changes in the program framework have been made and new features added to make it more flexible, robust, and complete. The reservoir element included in the program is used to represent any lake, detention basin, or reservoir with a storage-outflow relationship. The program now allows for explicit, physical description of each outlet from the reservoir. Transient events such as a dam failure can also be simulated. The new capabilities are implemented using an adaptive time-step, iterative solution of the continuity equation following Brent's method. The meteorologic model is responsible for processing all of the relevant atmospheric data to produce the boundary conditions for land-surface hydrology simulation. The framework previously supported only liquid precipitation and evapotranspiration processing. It has been expanded to include frozen precipitation and snowmelt as well. Most hydrologic simulation is performed using a top-down approach by assuming the meteorologic forcing is fixed. In the real world there are bi-directional feedback connections between different parts of the hydrologic cycle. Recent changes in the program framework make it possible to perform bottom-up simulation. The program framework that manages data and simulations has been made much more flexible and robust. Flexible because it allows the user to perform tasks in any order, and robust because it automatically handles data coordination issues. A new interface has been designed to make the most use of the improved framework. The interface is based on the concept of direct manipulation and allows the user to quickly find, view, and modify all of the data objects used in the program.