“To protect watershed health, understand the watershed as a Whole System,” says Dr. Richard Horner, University of Washington (Seattle)


Note to Reader:

Washington State research informed the early implementation of British Columbia’s Fish Protection Act (1997), the first legislation of its kind in Canada. In the mid-1990s, the pioneer work of Dr. Richard Horner and Dr. Chris May (University of Washington, Seattle) was transformational. Their findings resulted in a hydrology-based framework for protecting watershed health. The framework provided a starting point for applying science-based understanding to reinvent drainage engineering practice, commencing with release of Stormwater Planning: A Guidebook for British Columbia in 2002.


Watershed protection starts with an understanding of how water gets to a stream….

Richard Boase_March2015_500pWatershed protection starts with an understanding of how water gets to a stream from individual sites, how long it takes, and whether there are impacts along the way. The work of Richard Horner and Chris May was a catalyst for the Province of British Columbia to embrace the Water Balance Methodology some 15 years ago,” states Richard Boase, Environmental Protection Officer with the District of North Vancouver, and Co-Chair of the Water Balance Model for British Columbia initiative.

“The Water Balance Methodology links actions at the site scale with outcomes at a watershed scale. When the watershed goal is protection of aquatic resources, two decades ago Richard Horner and Chris May proved that it is necessary to first mitigate ‘changes in hydrology’ – that is, changes in how rainwater reaches streams. The Water Balance Methodology addresses flow path differences, and leads to solutions that would maintain watershed health. ”

A Watershed is a Whole System

1Richard Horner_120p“So many studies manipulate a single variable out of context with the whole and its many additional variables,” states Dr. Richard Horner, now an adjunct professor at the University of Washington. “We, on the other hand, investigated whole systems in place, tying together measures of the landscape, stream habitat, and aquatic life.” Richard Horner founded the Center for Urban Water Resources Management in 1990.

Four Factors Limit Stream Health

“In 1996, Richard Horner and Chris May published a seminal paper that synthesized a decade of Puget Sound research to identify and rank the four factors that degrade urban streams and negatively influence aquatic productivity and fish survival (Table 1 below). This science-based ranking provides a framework for Integrated Watershed Management,” reports Bill Derry. In the 1980s, he was one of the first stormwater utility managers in Washington State.

Bill Derry_2015_500pWhen published, this ranking (Table 1) shook conventional stormwater management wisdom in the Pacific Northwest to its foundation. This research made it clear that stormwater management was as much or more about land use decisions as engineering solutions. We also learned that we needed to address transportation choices.”

Bill Derry believed so strongly in the need for scientifically defensible research that he convinced his fellow utility managers to organize and fund the research centre founded by Richard Horner. Bill Derry communicated the science in a way that was easy for his audiences to understand. In the latter half of the 1990s, his teaching resonated with local governments in British Columbia.

Stormwater Magazine_article_4 factors

Work at Multiple Scales

Chris May_500pThe key to the Whole Systems approach is understanding the integrated significance of the three flow paths in a watershed – surface runoff, lateral interflow in shallow soils, and deep groundwater. Unlock that key and we can successfully implement appropriate measures so that creek systems are more resilient and therefore able to better cope with an altered flow regime,” continues Dr. Chris May. Previously the Urban Watershed Manager with Seattle Public Utilities, he is now Surface & Stormwater Division Director with Kitsap County Public Works in Washington State.

“We at Kitsap County have used this Whole Systems concept to develop our strategy for retrofit and rehabilitation – it is not sufficient to do only a single (or even a few) things – it is necessary to do everything! We know we need to work on multiple scales and on multiple fronts to improve conditions in our small stream watersheds – that’s our strategy.”


“The work of Richard Horner and Chris May is standing the test of time,” concludes Richard Boase. “The reason is that they applied systems thinking and looked at watersheds as a whole.”

To Learn More:

The most complete reference to all stream research undertaken by Richard Horner and Chris May is their final report to the United States Environmental Protection Agency, published in 2004.

Click on https://waterbucket.ca/cfa/files/2015/02/Ecological-Effects-of-Stormwater-and-Controls-on-Small-Streams-final-report_Mar-2004.pdf

For an historical perspective on implementation of the hydrology-based framework in BC, click on Rainwater Management in a Watershed Context – What’s the Goal?

Primer on Water Balance Methodology_Feb-2014_cover

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