Category:

Rainfall-Runoff Modeling

WHOLE-SYSTEM, WATER BALANCE TRAINING FOR ENGINEERS: “The Town’s experience is that the weak link in drainage analyses is always the assumptions,” stated Shelley Ashfield, Municipal Engineer, when she explained why the Town of Comox took on responsibility for an educational process to bridge a gap in practitioner understanding


How water gets to a stream, and how long it takes, is not well understood among land and drainage practitioners. “A lack of explicit identification and justification of the assumptions and simplifications made in the analysis of stormwater impacts has resulted in stormwater systems that address hypothetical as opposed to actual site characteristics and development impacts,” stated Shelley Ashfield. “Learning from this experience, the Town now requires that assumptions be stated and explained. We are saying WHAT is your assumption, and WHY.”

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VIDEO: “Maximum Extent Practicable, or MEP, has become the definitional driver for a lot of what we do,” said Andy Reese, engineer and writer who coined the term Voodoo Hydrology in 2006 to explain the pitfalls inherent in urban drainage practice


“Years ago I was privileged to travel around the US with EPA putting on seminars,” stated Andy Reese in 2011. “Three off-the-cuff words have probably have had the biggest impact in influencing land design of any sort of regulatory program that ever was, and perhaps that ever will be. Those three words were maximum, extent and practicable. Back then, none of those words were capitalized. They were just a made-up term. But MEP is now taking on green infrastructure overtones, sustainability overtones, LID overtones, and on and on.”

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Global runoff volumes are increasing dramatically, according to a new Columbia University study (2018): “Our findings can help provide scientific guidance for infrastructure and ecosystem resilience planning and could help formulate strategies for tackling climate change,” stated Dr. Pierre Gentine


Columbia Engineering researchers have demonstrated that stormwater runoff extremes have been dramatically increasing in response to climate change and other anthropogenic changes to the environment. The researchers also found that storm runoff has a stronger response than precipitation to human-induced changes (climate change, land-use land-cover changes, etc). “Our work helps explain the underlying physical mechanisms related to the intensification of precipitation and runoff extremes,” Pierre Gentine said. “

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EDITORIAL: When does a road become a river? Why hydrologists and water planners need to move beyond averages – Australasian Journal of Water Resources (July 2018)


A river can be defined as ‘A large natural stream of water flowing in a channel to the sea, a lake or another river’ or more simply as ‘A large quantity of a flowing substance’. Obviously, under the second definition a road could be defined as a river and potentially under the first if again our interpretation of ‘natural’ is as flexible as current common usage! Why is such a seemingly silly and perhaps confusing question important?” stated Katherine Daniell.

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Restore Watershed Hydrology and Re-Set the Ecological Baseline: “A goal of the IREI program is to embed state-of-the-art hydrology in engineering ‘standard practice’,” says Kim Stephens, Partnership for Water Sustainability


“Among land and drainage practitioners, how water gets to a stream and how long it takes is not well understood. Unintended consequences of this failure to ‘get it right’ include degraded urban streams, more flooding, more stream erosion, less streamflow when needed most, and an unfunded infrastructure liability,” states Kim Stephens. “In 2006, American engineer and textbook author Andy Reese coined the term voodoo hydrology to both describe drainage practice and draw attention to the need for changing the way drainage engineers practice their trade.”

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Voodoo Hydrology Annual Webinar Series (December 2017): Andy Reese explains the pitfalls of urban hydrology methods


Andy Reese coined the term Voodoo Hydrology in 2006. “As a stormwater community, we have for years relied upon common urban stormwater hydrologic design methodologies and trusted their results. But, should we? We must understand that urban hydrology, including newer Green Infrastructure sizing approaches, as commonly practiced, is an inexact science where we are simply trying to get close to the right answer,” states Andy Reese.

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IMPLEMENTATION OF WHOLE-SYSTEM, WATER BALANCE APPROACH: “The challenge is to move from stop-gap remediation of in-stream problems to long-term restoration of a properly functioning watershed,” stated Peter Law, Vice-President of the Mid Vancouver Habitat Enhancement Society


“By sharing the story of Shelly Creek, we want readers to recognize that erosion is a common issue impacting salmon and trout habitats in small streams, draining into the Salish Sea,” states Peter Law. “Existing standards of practice have resulted in negative impacts. Continuing to use those standards will result in further environmental degradation of the watershed and loss of stream productivity. Building support for action starts with community engagement.”

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FLASHBACK TO 2012: "A key challenge has been translating global climate science to local land-use decisions. The new Climate Change Module in the Water Balance Model helps overcome this obstacle,” stated Chris Jensen, Senior Policy Analyst, Government of British Columbia


“If mitigation is about CARBON, then adaptation is about WATER. Hence, being able to quickly and effectively model how the ‘water balance’ may change over time is a critical input to local government decision processes,” stated Chris Jensen. ” We heard from communities that they desired an easy to use tool, one that would help them understand and identify evaluate options for climate adaptation. This need served as a catalyst for development of the Climate Change Module.”

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LEADING CHANGE: British Columbia's Water Balance Methodology – Coming to Terms with "Voodoo Hydrology"! (Forester University Webinar on May 2, 2017)


The Water Balance Methodology has its genesis in the whole-system approach that Dr. Ray Linsley (1917-1990) championed more than 60 years ago. As a professor at Stanford University, he pioneered the development of continuous hydrologic simulation as the foundation for water balance management. In the 1960s, Linsley championed the paradigm-shift from empirical relationships to computer simulation of hydrologic processes.

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United States EPA funds creation of Center for Infrastructure Modeling & Management: “British Columbia experience in whole-system, water balance based approaches in the Pacific Northwest adds a critical combination of tools and understanding to the water resources toolbox,” states Dr. Charles Rowney, Director of Operations


“It is the combination of diverse needs, ideas and solutions that will make the vision for the Center work,” stated Dr. Rowney. “That is one of the reasons we’re so pleased with the agreement just reached with the British Columbia Partnership for Water Sustainability. We have many needs in common, and many ideas to share. The leadership shown by the Partnership has led to a body of knowledge from which others can learn.”

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