WMS:HEC-HMS

Overview

The Hydrologic Modeling System (HMS), written by the Hydrologic Engineering Center (HEC), simulates a watershed's rainfall-runoff process. It is designed to replace HEC-1, and has similar options to HEC-1, but incorporates some advances in hydrologic engineering. These advances include (1) a linear quasi-distributed runoff transform (called ModClark) for use with gridded precipitation, (2) continuous simulation capabilities with either a one-layer or more complex five-layer soil moisture method, and a parameter estimation option. HMS also incorporates a graphical user interface (GUI) for entering hydrologic data, where HEC-1 data was entered using text input files. WMS 7.1 and later versions provide tools for setting up, computing data for, and entering data for HMS models. These models can then be saved to HMS format and the model can be run in HMS. The results from these models can then be read into and viewed in WMS.

You may wonder why you would set up and run an HMS model in WMS when you can just do it in HMS. The reason you would do this is because WMS provides GIS, watershed modeling, and HMS parameter computation capabilities all in one place, while HMS does not provide this.

The HEC Data Storage System (DSS) is a format that was previously unsupported in WMS. Since HMS uses this format for importing and exporting time series data, WMS 7.1 and later versions now support importing and exporting DSS files, allowing for reading and writing time series data from and to HMS.

All the HMS data is entered using one of three dialogs. These dialogs are meant to correspond to the three different types of data entered in HMS: The HMS meteorologic data, the control data, and the basin data. The first dialog used in WMS is the HMS Properties dialog, shown below:

File:WMSimage6.jpg

The second is the HMS Meteorologic Model dialog, shown below:

File:WMSimage7.jpg

The final dialog is the HMS Job Control dialog:

File:WMSimage8.jpg

HEC-1 / HEC-HMS Comparison

HMS includes most of the same capability as HEC-1, but has dropped some of the lesser used functions and added others. You can use WMS to delineate watershed data and define most parts of the HMS model. The Export HMS Basin File found in the HEC-1 menu will create the input file necessary to use data derived in WMS to perform modeling in HMS.

There are five different files that are (or can be) exported as part of the HMS simulation.

1. The Project file is like the WMS super file in that it is used to keep track of the other files that make up the HMS simulation.
2. The Control file includes the job control data, or simulation global parameters such as time step, number of ordinates, id cards, etc.
3. The Basin file has all of the parameters for each hydrologic unit (basin, outlet, diversion, etc.).
4. The Precipitation file contains the information used to define the precipitation event for the simulation.
5. The Map file is a map or trace of the watershed and sub-basin boundaries. It is not a terrain model and therefore cannot be used to extract information such as area or runoff distance; it is only a "picture" of the watershed that is placed as a backdrop to the HMS schematic. If you have a watershed derived in WMS from a digital terrain model then you can export it as part of your HMS project. In order to export the map you must convert it to feature objects. If you create your watershed from feature objects or a DEM then it will already be in this format. If you create your watershed from a TIN then you will need to use the Drainage Data -> Feature Objects command found in the Drainage menu prior to exporting your HMS files.

Related Topics:

• Opening an HMS File
• Post Processing HMS Results
• Running HMS
• Saving an HMS File
• HMS Properties Dialog
• Job Control
• Saving HEC1 Files
• Running an HEC-1 Analysis