HEC-HMS (the Hydrologic Engineering Center's Hydrologic Modeling System) simulates watershed hydrology, hydrograph routing, and water-control elements. Depending on the selected methods and inputs, it estimates runoff volume, peak flow, hydrograph timing, reservoir storage and releases, and erosion and sediment transport. The table summarizes selected capabilities and links to the current documentation; it is not an exhaustive inventory for every software version.

Summary of Simulation Methods included in HEC-HMS

Category and documentation

Selected capabilities

Precipitation and evapotranspiration

Observed, gridded, interpolated, and hypothetical meteorological inputs; choose a representation appropriate to the event or continuous simulation.

Snowmelt

Temperature-index methods for snow accumulation and melt, including gridded representation.

Canopy, surface storage, and infiltration losses

Methods with differing data needs and event/continuous applicability. Loss options include Initial and Constant, SCS Curve Number, Green and Ampt, Deficit and Constant, Linear Deficit and Constant, and Soil Moisture Accounting; this list is selective.

Direct-runoff transformation

Unit-hydrograph methods, ModClark, Kinematic Wave, and 2D Diffusion Wave represent runoff translation and attenuation with different spatial detail and assumptions.

Baseflow

Methods representing slower subsurface contributions, including Recession and Linear Reservoir.

Reach routing

Hydrologic routing methods such as Lag, Modified Puls, Muskingum, and Muskingum-Cunge. Review each method's assumptions and suitability for the reach.

Reservoirs and water-control elements

Reservoir storage and outflow routing, including Outflow Curve, Outflow Structures, Specified Release, and Rule-Based Operations; diversions represent transfers from the main flow path.

Erosion and sediment transport

Subbasin sediment yield, reach transport, and reservoir sediment processes, with method-specific sediment inputs and outputs.

Select methods for their physical assumptions, required data, and ability to provide the decision information. HEC-HMS includes a 2D Diffusion Wave subbasin transform, while its reach routing methods implement hydrologic routing rather than the full unsteady hydraulic equations. Detailed channel hydraulics, backwater, structures, or inundation mapping may require a companion model such as HEC-RAS; see Are Other Methods Required?.

Current HEC-HMS.

Beyond individual process methods, HEC-HMS provides Forecast Alternatives, the Combined Parameter Editor, forecast optimization, and Ensemble Simulations. These support forecast adjustments and analysis workflows; their availability and setup depend on the installed version.

The HEC-HMS User's Manual explains setup and use. The HEC-HMS Technical Reference Manual describes the methods, equations, assumptions, and parameter estimation.