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“The need to embrace LID practices arose from the need to prevent further increases in damage to both the environment and the agricultural community resulting from the increases in runoff from urban areas. The Neighbourhood Concept Plan (NCP) established rainfall capture objectives for maintaining the predevelopment runoff rates and volumes. The first phase of development brought the need to create calculation methods to verify that the designs complied with the NCP requirements,” stated Jim Dumont.

“The ‘Water Balance is a term that has been widely adopted by many; however, there are also many different meanings and methods for its application. In this article, I describe four different approaches to a so-called ‘water balance approach’,” stated Jim Dumont. “For each approach, I provide a very simple introduction so that the reader will have a sense of what each approach involves. My purpose is to provide a contrast with the approach we have been developing and adopting in British Columbia.”

“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.”

A decade ago, three neighbourhood developments in Langley established successive provincial precedents that informed the evolution of the Water Balance Methodology. “Langley is unique in that DFO approved the water balance strategy at a neighbourhood scale for each of Routley, Yorkson and Northeast Gordon,” stated Jim Dumont. “DFO approval meant that design standards were applied uniformly across each neighbourhood. This was a time-saver for everyone. The approach resulted in consistency of implementation.”

Flood, drought, fire, wind and cold – because extreme events are becoming the norm…..As communities face the increasing impacts of climate change, there is an unfunded liability – the cost to restore watershed hydrology and water resilience in the built environment. “The Partnership for Water Sustainability is evolving, online tools that support implementation of the whole-system, water balance approach. British Columbia, Washington State and California are leaders. We are moving forward in parallel on this journey,” states Jim Dumont.

The Partnership for Water Sustainability in British Columbia partnered with Forester University to share, via webcast, the British Columbia innovation and experience that has resulted in the whole-system, water balance approach. “We are delighted to have Kim Stephens and Jim Dumont share British Columbia’s cutting-edge continuous simulation model, known as the Water Balance Methodology,” stated Emily Shine. “At Forester University, we aim to position ourselves at the forefront of innovation in rainwater management and green infrastructure, and that is why we are calling Water Balance Methodology a webinar that cannot be missed.”

The agreement is to collaborate regarding reciprocal benefits and joint actions related to water resources research and practice in North America. The focal point for cross-border collaboration is the new US-based Center for Infrastructure Modelling & Management, the new home for SWMM. “Tools like SWMM and QUALHYMO can enable the hydrologic computations; it is up to us to recognize the need, and to deliver tools that facilitate the analysis. I expect that discussions about methodology will be as much a part of the Centre as the development of new code,” states Jim Dumont.

“So what is the nub of the issue? In standard practice, only surface runoff is considered, and this has led to degraded streams. If communities are to truly benefit from use of nature’s assets to provide vital community infrastructure services, then two issues must first be recognized as being impediment to changes in practice,” stated Jim Dumont. “Issue #1 is widespread lack of understanding of the relationship between flow-duration and stream (watershed) health. Issue #2 is widespread application of a standard of practice that has little connection to real-world hydrology.”

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. What makes BC’s stormwater approach different than other jurisdictions; particularly the U.S., he wondered?

“Breakthroughs in science-based understanding occurred in the mid-1990s. Yet engineering practice generally did not incorporate this understanding. The Water Balance Methodology has addressed this historical oversight and is being enhanced over time to incorporate fresh insights,” stated Jim Dumont. “If the stream flows and durations of flow can be maintained without increasing the magnitude and duration of above average stream discharges, then success can be demonstrated.”