HEC-HMS (Hydrologic Modeling System) 3.5, User's Manual

This manual is a user's guide to the following program:
Corps of Engineers' recently released Hydrologic Modeling System (HEC-HMS) Version 3.5. HEC-HMS is designed to simulate the precipitation-runoff processes of dendritic watershed systems. It is the successor to HEC-1 and provides a similar variety of options but represents a significant advancement in terms of both computer science and hydrologic engineering. In addition to unit hydrograph, hydrologic and reservoir routing options, capabilities include a linear quasi-distributed runoff transform (Mod Clark) for use with gridded precipitation, continuous simulation with either a one-layer or more complex five-layer soil moisture method, and a versatile parameter estimation option. The software is designed for interactive use in a multi-tasking, multi-user network environment, and can be used with both X-Windows and Microsoft Windows.
The program is a generalized modeling system capable of representing many different watersheds. A model of the watershed is constructed by separating the hydrologic cycle into manageable pieces and constructing boundaries around the watershed of interest. Any mass or energy flux in the cycle can then be represented with a mathematical model. In most cases, several model choices are available for representing each flux. Each mathematical model included in the program is suitable in different environments and under different conditions. Making the correct choice requires knowledge of the watershed, the goals of the hydrologic study, and engineering judgment.
The program features a completely integrated work environment including a database, data entry utilities, computation engine, and results reporting tools. A graphical user interface allows the seamless movement between the different parts of the program. Program functionality and appearance are the same across all supported platforms.
HEC-HMS provides a variety of options for simulating precipitation-runoff processes. In addition to unit hydrograph and hydrologic routing options similar to those in HEC-1, capabilities currently available include: a linear-distributed runoff transformation that can be applied with gridded (e.g., radar) rainfall data, a simple "moisture depletion" option that can be used for simulations over extended time periods, and a versatile parameter optimization option. The latest version also has capabilities for continuous soil moisture accounting and reservoir routing operations.The primary new features include:
* Subbasin elements include new canopy and surface simulation components.
* A gridded Green Ampt loss rate method has been added.
* A simulation run can now be imported, bringing all necessary data with it.
* The Muskingum-Cunge channel routing method has been improved.
* The diversion element includes new options for simulating diversion flow.
* The background maps can now be displayed conditionally, depending on zoom level.
* The Green Ampt component is now more consistent with soil physics terminology.
* The range of use for the pump component has been increased.
* The temperature index snowmelt method has been improved.
* Specified release method for reservoir routing
* Radial and vertical gates added to reservoir spillways
* New optional parameter for orifice outlet in reservoir
* New Smith-Parlange loss rate method in subbasin
* New nonlinear Boussinesq baseflow method in subbasin
* Lateral weir and pump station methods for diversion
* Optional stage calculations added to two routing methods
* Channel losses added to reach