Download page What is HEC-HMS and what is its Role?.
What is HEC-HMS and what is its Role?
HEC-HMS is a numerical model (computer program) that includes a large set of methods to simulate watershed, channel, and water-control structure behavior, thus predicting flow, stage, and timing. The HEC-HMS simulation methods, which are summarized in the table below, represent:
Watershed precipitation and evaporation. These describe the spatial and temporal distribution of rainfall on and evaporation from a watershed.
Runoff volume. These address questions about the volume of precipitation that falls on the watershed: How much infiltrates on pervious surfaces? How much runs off of the impervious surfaces? When does it run off?
Summary of Simulation Methods included in HEC-HMS
Category
Method
Precipitation
User-specified hyetograph
User-specified gage weighting
Inverse-distance-squared gage weighting
Gridded precipitation
Interpolated precipitation
Frequency-based hypothetical storms
Standard Project Storm (SPS) for Eastern United States
Hypothetical storm
Evapotranspiration
Monthly Average
Priestly-Taylor
Penman Monteith
Hamon
Hargreaves
Interpolated ET
User-specified
Snowmelt
Temperature Index
Gridded Temperature Index
Runoff-volume
Initial and constant
SCS curve number (CN)
Gridded SCS CN
Green and Ampt
Layered Green and Ampt
Exponential
Smith Parlange
Deficit and constant
Gridded deficit and constant rate
Soil moisture accounting (SMA)
Gridded SMA
Direct-runoff
User-specified unit hydrograph (UH)
Clark's UH
Snyder's UH
SCS UH
ModClark
Kinematic wave
User-specified s-graph
2D Diffusion Wave
Baseflow
Constant monthly
Exponential recession
Linear reservoir
Nonlinear Boussinesq
Routing
Kinematic wave
Lag
Modified Puls
Muskingum
Muskingum-Cunge
Water control structures
Diversion
Reservoir/detention pond
Direct runoff, including overland flow and interflow. These methods describe what happens as water that has not infiltrated or been stored on the watershed moves over or just beneath the watershed surface.
Baseflow. These simulate the slow subsurface drainage of water from a hydrologic system into the watershed's channels.
Channel flow. These so-called routing methods simulate one-dimensional open channel flow, thus predicting time series of downstream flow, stage, or velocity, given upstream hydrographs.
The HEC-HMS methods are described in greater detail in the HEC-HMS Technical Reference Manual (HEC, 2000). That manual presents the concepts of each method and the relevant equations that are included. It discusses solution of the equations, and it addresses configuration and calibration of each method.