Note to Reader:
The following story comprises two parts. First, the “Water Balance Model Express for Landowners” (WBM Express) is introduced. This web-based scenario comparison and decision support tool was developed by the Partnership for Water Sustainability in British Columbia. In part two, the Water Balance Methodology for populating the WBM Express with a set of three watershed target values is explained.
The WBM Express is incorporated in the curriculum for an online course on Urban Watershed Management at the University of British Columbia. The faculty members who teach the Master of Land and Water Systems Program have developed an online tutorial that provides step-by-step guidance on use of the WBM Express.
To access the YouTube video about the WBM Express, click on the image below. Separate videos demonstrate how to use GEOweb open data portal developed by the District of North Vancouver. Scroll down.
Mimic the Natural Water Balance to Protect Watershed Health
Funded by Metro Vancouver and a federal-provincial program for climate change adaptation, the Water Balance Model Express for Landowners provides local governments with the capability to protect stream health by implementing Water Balance targets at the site scale. This means slow, sink and spread rainwater.
GEOweb is a mapping information tool. Developed in-house by the District of North Vancouver, the GEOweb Geographic Information Systems (GIS) database allows users to identify a property using orthophotographs taken at various intervals from 1992 to the present.
“The innovative online format of GEOweb and the WBM Express makes them very accessible,” reports Julie Wilson, instructor in Urban Watershed Management at UBC
“When our long term collaborator at the District of North Vancouver, Richard Boase, informed us of some of the new tools available to support rainwater management and planning in the District, I immediately knew I wanted to incorporate them into an assignment for the course,” states Julie Wilson. She is the instructor for the online course, Urban Watershed Management, created by Dr. Hans Schreier, Professor Emeritus in the Faculty of Land and Food Systems at the University of British Columbia.
“Being fully accessible online, the GEOweb mapping information tool and the Water Balance Model Express were ideally designed for students in the Urban Watershed Management course, as many of them are remotely based across Canada and internationally.”
“So I went to work creating an assignment based on a real property in the Lynn Valley area of North Vancouver that is undergoing some form of re-development. To help familiarize the students with the layout of the tools, I worked with Richard Boase to create a few online video tutorials to introduce GEOweb and the WBM Express.” To access the YouTube videos about GEOweb, click on the two images below.
Description of Student Assignment
“The assignment was to assess a property for changes in development over time, and see how beneficial management practices can mitigate rainwater runoff and associated impacts,” continues Julie Wilson.
“GEOweb allowed students to identify a property in the Lynn Valley area that had visibly changed as a result of redevelopment, resulting in an increased impervious surface on the property.”
“Using tools in GEOweb’s ‘Properties Application’, students delineated and estimated impervious areas on the property before and after re-development. This information was then input into the WBM Express in order to model runoff and potential impacts to stream health. The students then were asked to make changes to the property by adding rainwater capture components (such as rain gardens and infiltration swales), and report on the differences in the stream health indicator.”
What the Students Learned
“The students appreciated the power and utility of these kinds of tools to engage with the public on issues of development and rainwater management,” reports Julie Wilson.
“The innovative online format of both tools makes them very accessible, and would be very useful to convey the value of retaining vegetation and using landscape-based features, by illustrating these concepts with a homeowner’s very own property.”
Student Feedback – Quotable Quotes:
- “The potential for this type of software to educate the public about watershed health is incredible. Once the public and builders are educated about what kind of changes they can make to their properties, and the associated benefits of these changes, this type of software will be of a great benefit to local watersheds.”
- “Overall I see this tool as a pioneering instrument to educate and connect with the general public regarding how their actions at the property scale can impact or relate to overall stream health.”
- “Overall, GEOweb and the WBM Express are useful tools which help consider rainwater management in relation to residential development.”
Flood on November 3, 2014
“This was also a very timely assignment, as shortly after the students completed it, the heavy rainfall event on November 3rd in North Vancouver resulted in localized flooding in Lynn Valley, the very same area where the properties in the assignment were based.”
“The students really made the connection between urban flood risk and impervious area in the watershed, especially when coupled with steep terrain, shallow soils, wet antecedent conditions and an intense rainfall event (PLUS in this situation, a lack of snowpack to absorb and delay some of the rainfall).”
“It was very unfortunate that one of our students was directly affected by the flood water and debris of this event, but it emphasized the importance of rainwater management and watershed management,” concludes Julie Wilson.
Water Balance Methodology & Performance Targets
The calculator engine for the WBM Express is populated with a set of three water balance performance targets (i.e. Watershed Targets):
- The three Watershed Targets are retention volume, baseflow release rate, and infiltration area.
- Values for the three are established and input by the local government; and are determined pursuant to the Water Balance Methodology for Protecting Stream Health.
- The WBM Express integrates and balances the three targets. It DOES NOT estimate runoff.
- It is a tool that provides an assessment of how well a property is doing in achieving the Watershed Targets. The two concepts are completely different.
The question MUST be framed in terms of “What do we need to do on a site to allow it to mimic the natural environment?” This is a much different question than “how much runoff volume?”, and one that leads to the desired answer much more quickly.
“A decade ago, looking at rainfall differently led the Province to initiate a change in the way rainwater is managed. In 2002, introduction of the Water Balance Methodology was a catalyst to trigger actions on the ground that would maintain or restore the natural Water Balance. The initial priority was to reduce surface runoff volume,” states Peter Law, Chair of the Guidebook Steering Committee and a founding Director of the Partnership for Water Sustainability in British Columbia.
“Then, in 2007, the Beyond the Guidebook initiative enhanced the Water Balance Methodology to address the relationships between volume of rainwater captured and held on site, release to interflow, and resulting flow rates in streams.”
“By 2012, Beyond the Guidebook had also addressed the relationship between volume of rainwater captured and groundwater recharge. Application of the Water Balance Methodology enables local governments to establish a set of three watershed-specific and integrated Performance Targets.”
“Since 2012, the focus of the Beyond the Guidebook initiative has been on how to integrate and implement performance targets that result in balanced solutions. The key to mimicking the hydrology of a natural watershed is to replicate the shallow soil storage and conveyance system.”
Demonstrate Effectiveness of Mitigation Measures
“The water balance of a watershed is complex. There are three pathways by which rainwater reaches streams: surface runoff, interflow in shallow soils, and deep groundwater, ” continues Jim Dumont, the Partnership’s Engineering Applications Authority.
“The water balance of a watershed is a topic which has suffered from descriptions that oversimplify the processes to such an extent that unintentional adverse consequences may be occurring as a result of application of commonly employed prescriptive practices. A goal of the Partnership in evolving the Water Balance Methodology is to address and rectify this issue of concern.”
“Surface runoff is a small component of natural watershed function. The key to replicating watershed function and mitigating impacts is understanding ALL flow paths through the landscape. Then, Watershed-based Targets can be distilled into a set of design values that are easily applied at a lot level.”
“An integrated design for land development, rainwater management and groundwater recharge would balance the annual volume necessary for interflow storage with the annual volumes necessary to sustain the duration of interflow and allow infiltration to groundwater.”
“The Water Balance Methodology provides a logical and straightforward way to assess potential impacts resulting from urban development; and analytically demonstrate the effectiveness of the methods proposed for preventing and/or mitigating those impacts.”
“The Primer on the Water Balance Methodology lays the foundation for the integration of watershed information into a system of analysis that allows a practitioner to describe how the streams in a watershed are impacted by urban development.”
To Learn More:
Released in February 2014 by the Partnership, the Primer on Water Balance Methodology for Protecting Watershed Health is primarily written for a technical audience, and provides the water resource practitioner with how-to-guidance for applying an analytical process to establish the three Watershed-based Targets that “mimic the Natural Water Balance”.
In April 2014, the Partnership released a supplementary guidance document titled “An Introduction to the Water Balance Methodology for Protecting Watershed Health”.
A graphic representation of the application of the three targets can be envisioned in the graphic below of a typical rain garden. Note how the three watershed targets can be readily identified in the different parts of this standard installation.