Many HEC-HMS models integrated into HEC-RTS for real-time forecasting were originally developed for detailed studies, not for operational use. As a result, these models often contain more detail and generate larger files than necessary for real-time applications. Even when models were initially intended for real-time forecasting, excess detail from early development phases can lead to bloated file sizes and longer forecast creation times. Over time, repeated forecast creation and model duplication can unnecessarily consume disk space and slow performance.

This guide will walk you through techniques to streamline your HEC-HMS model by identifying and removing unnecessary files and outputs to save disk space, reduce forecast creation time, and improve project portability.

Only remove files and components explicitly mentioned in this guide. Many files are essential for model operation.

Prerequisites

This guide uses WinDirStat. 

USACE personnel can install it via the App Portal.

Step 1: Backup your Model

Always create a backup of your HEC-HMS model before making any changes.

Step 2: Analyze the Model Directory with WinDirStat

  1. Open WinDirStat and point it to the HEC-HMS folder (<watershed name>\hms).
  2. Let the scan complete to visualize folder and file sizes.
  3. In the example shown above:
    1. Total project size: ~1.4 GB
    2. Key contributors:
      1. files (direct project files): ~40%
      2. terrain: ~20%
      3. results: ~10%
    3. Folders like gis, ensemble, and datavar contribute minimal size and can be ignored in this example.

Step 3: Evaluate and Reduced HEC-DSS File Size

  1. Expand the files option in WinDirStat to inspect any .dss files.
  2. Identify large .dss files (e.g., ExampleModel.dss, NWK_Osage2.dss, NWK_Osage.dss).
  3. Open the ExampleModel.dss file using HEC-DSSVue.
  4. Remove any datasets with an F Part of FOR: from the file.
    1. Use the filters to find all pathnames that include FOR: in the F Part.
    2. Select the necessary records.
    3. From the Edit menu, select Delete Records.
  5. Squeeze the file by selecting Squeeze from the Tools menu.
    1. The file size was reduced from 165 MB to 133 KB in this example.
  6. If other .dss files (e.g., NWK_Osage.dss, NWK_Osage2.dss) appear unused:
    1. Temporarily delete them and open HEC-HMS.
    2. If prompted with a Missing File References message, the file is still needed.
    3. You can manually confirm by going to the File menu in HEC-HMS and selecting References.
      1. If any of the missing references point to the .dss file you deleted, the file was needed and should be replaced in the directory.

Step 4: Trim the Results and Terrain Folders

  1. Delete all .tilecache files in the hms\results folder. They are used only for spatial results visualization and can be regenerated.
  2. Delete all .log files. These are safe to remove and regenerate as needed.
  3. For models using HEC-HMS 4.12+, terrain is no longer copied with each forecast, so trimming this is less critical.

While terrain doesn't impact disk space in forecast runs, simplifying it can improve map rendering and reduce simulation time.

Step 5: Target Smaller, Redundant Files

Even small files can accumulate and impact performance:

  1. Remove outdated components (e.g., extra basin models, test elements).
  2. Reduce the number of discharge gages and simplify input sources to what’s essential for forecasting.
  3. Consolidate gage data into fewer .dss files (e.g., one .dss file for all discharge/stage gages instead of one per gage).
  4. After cleanup, cross-reference the global file references (File → References) and delete unreferenced .dss files.

In the example, model size was reduced from 1.4 GB to 600 MB, a nearly 60% reduction.

Best Practices and Recommendations

  • Preserve calibration/validation data outside of the operational model. Store a backup with all historical data before cleanup.
  • Iteratively refine your model by removing components in phases.
  • Maintain a clean directory structure and periodically review project files.

Final Review

By cleaning up your HEC-HMS project, you can:

  • Save hundreds of megabytes of storage per model
  • Speed up forecast creation in HEC-RTS
  • Improve performance when transferring or archiving models
  • Simplify troubleshooting and model maintenance

Small changes lead to big gains. A leaner HEC-HMS model means faster, more efficient real-time forecasting.

Additional Resources

Refer to the Reducing Your Project's Footprint tutorial that focuses on managing GIS files within an HEC-HMS model.