Western Washington Hydrology Model

Version 3.0 is available

Thank you for evaluating WWHM (version 2.0). The program has been redesigned to provide the flexibility to handle unequal pre-developed and post-developed areas and the capability to simulate multiple ponds and basins. In addition, the program has an "Autopond" algorithm that can generate pond designs that in most cases will be optimally sized to pass the flow duration standard. The program can also generate design flow rates and volume for use in sizing stormwater treatment BMPs.

Under Help\Content\ there is a "Quick Start" option that provides an overview of the program features and operation.

WWHM2 Download and Installation Instructions (7-28-03) (PDF)

NOTE: Some Windows 2000 users have experienced installation difficulties with  wwhm2.5e. You may try installing the wwhm2.6 version by downloading "WWHM2.6Setup.msi" and "allmaps.zip". When downloading these files, please remember not to save the downloads in C:\Program Files\WWHM2 folder. (However, allow WWHM2 program to be installed in C:\Program Files\WWHM2 folder).

DRAFT Western Washington Hydrology Model Version 2.1 User's Manual

Suggested procedures for sizing Infiltration Ponds using WWHM (PDF)


wwhm2-patch-to-update-version-2.5e-to-2.5f.exe (NOTE: When using "File/New Project," please go to "View/Preferences/MISC" and click on "Restore Defaults" and then "UPDATE." This will make sure that the "Pan Evap" is correctly set to "0.76." This bug was recently found and occurs only if you use "File/New Project.") The patch below will fix this bug and update WWHM2.5e to WWHM2.5f. To use the patch you must (1)- have already setup WWHM2.5e on your computer; (2)- download the patch and double click on it and unzip it in the default C:\Program Files\WWHM2 folder.

wwhm2-patch-to-update-version-2.5e-to-2.5f.exe Download and double click on this patch to unzip it in the default C:\Program Files\WWHM2 folder. This will fix a bug and update WWHM2.5e to WWHM2.5f.

Check out county updates below

Major items in the 1-12-04 update:

Based on a December 2003 report by MGS Engineering Consultants, Inc., the relationship for converting the water quality design flows from hourly to 15 minute flows has been updated. The new relationship has been developed using 25 years of actual 15-minute precipitation data from a Seattle Public Utility gage located near the University of Washington Hydraulics Laboratory in Seattle. This new relationship is shown below:

For mixed till and outwash sites, the 15-minute to 60-minute ratio can be expressed as a weighted average of the till and outwash areas:

R15/60 = 1.13*Woutwash + Wtill *[ 1.00 + 0.13*(imperv) ]

where: Woutwash is the fraction of the site that contains outwash deposits; Wtill is the fraction of the site underlain by till, and Woutwash + Wtill = 1 ; and imperv is the fraction of the site covered by impervious surfaces.

Summaries of the previous updates


County map files for Version 2.0:

Clallam (updated 8/28/03) Kitsap (updated 7/18/03) Skagit
Clark Lewis Skamania (updated 12/12/02)
Cowlitz Mason Snohomish
Grays Harbor Pacific Thurston
Island (updated 12/12/02) Pierce Wahkiakum
Jefferson (updated 8/28/03) San Juan Whatcom (updated 2/12/03)

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