Category:

Rainfall-Runoff Modeling

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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LOOK AT DRAINAGE DIFFERENTLY: "We have a standard-of-practice that is generally accepted as not achieving what is best for the environment," stated Jim Dumont at the 2017 Comox Valley Eco-Asset Symposium


“So what is the nub of the issue? In standard practice, only surface runoff is considered, and this has led to degraded streams. The other pathways by which rainfall reaches streams are ignored,” explained Jim Dumont. “If communities are to truly benefit from use of nature’s assets to provide vital community infrastructure services, then we must change the engineering standard-of practice to one that is state-of-the-art and reflects real-world hydrology.”

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Interview offers insight into 'watershed / stream' approach: Watershed objectives start with the stream and end with the stream, say Jim Dumont & Kim Stephens


James Careless had an assignment to look into stormwater modelling tools (for projecting flow and other patterns); both to determine the most common tools used, and some of the most innovative approaches that are coming into use. His research into BC’s water balance approach led him to switch gears from an examination of modelling tools to learning what ‘establishing watershed objectives for stormwater management’ means in practice.

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Water Balance Methodology: "Watershed objectives start with the stream and end with the stream," says Jim Dumont, the Partnership's Engineering Applications Authority


“The Water Balance Methodology is based upon watershed and stream function and operation. Understanding how precipitation makes its way to the stream allow us to assess how a watershed and stream operates and to analytically demonstrate impacts of development and the effectiveness of any mitigation works,” states Jim Dumont. “The Methodology provides solutions with verifiable results and where mitigation systems optimized for cost and function.”

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United States EPA: Modelling study demonstrates that "green infrastructure = flood resilience"


“Research has demonstrated the water quality and channel protection benefits of GI; however, the effect of reducing the severity of flood events has not been investigated at a watershed level,” said Dr. Dan Medina. “The EPA posed this question – would the combined effect of thousands of rain gardens designed to capture relatively small volumes of runoff lead to a significant reduction in flood risk? The answer to this question is YES.”

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Voodoo Hydrology Annual Webinar Series (January 2016): “The rise of Green Infrastructure and Resilience Planning opens the door for newer Voodoo like never before,” observes Andy Reese, water resources engineer and author


“All uses of rainfall instead of flow data make the ‘Big Assumption’,” states Andy Reese. “This is a problem, because there are an infinite number of combinations of all the variables within the watershed we have to estimate to try to arrive at that one peak flow. So we must make simplifying assumptions about everything that affects stormwater volume and that moderates its flow rate.”

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