Water Balance Model insights inform New Zealand delegation
New Zealand Reaches Out to District of North Vancouver
The Institute for Resources, Environment and Sustainability at the University of British Columbia recently facilitated an exchange of information between the District of North Vancouver and a delegation from New Zealalnd.
According to Dr. Hans Schreier of UBC, “When Dr. Maggie Lawton of Manaaki Whenua Landcare Research asked which local government should she talk to about their use of the Water Balance Model, my first response was the District of North Vancouver. Richard Boase of the District is a leading advocate of this tool, and is a member of the Water Balance Model Training Team that conducts workshops province-wide. So he was a natural for the New Zealanders to meet.”
Manaaki Whenua – Landcare Research is New Zealand’s foremost environmental research organisation specialising in sustainable management of land resources optimising primary production, enhancing biodiversity, increasing the resource efficiency of businesses, and conserving and restoring the natural assets of New Zealand communities. According to Dr. Lawton, the mission of her organization is “Science making a difference for a truly clean, green and sustainable New Zealand.”
To provide a framework for information sharing with the New Zealand delegation, Richard Boase prepared a slideshow that illustrates the direction in which the District of North Vancouver is heading in order to achieve watershed health objectives.
“The key is what we do at the site scale”, said Boase, “because our actions over time can either have cumulative impacts or cumulative benefits. Drawing on the District’s GIS resources, I was able to identify representative properties from different eras – 50 years ago and today – to illustrate how the current approach to site development results in dramatically greater volumes of surface volume. I was also able to demonstrate the benefits of landscape-based source controls in reducing runoff volumes to acceptable levels.”
To view the presentation, click on District of North Van – SF Rainwater Management
THE WAY PROPERTIES WERE ONCE DEVELOPED is illustrated by the representative property below. This shows the extensive tree canopy coverage (53%) versus the relative small percentage (32%) of hard surfaces.
THE WAY PROPERTIES ARE CURRENTLY BEING DEVELOPED is illustrated below. In this example, the only reason there is still a portion of tree canopy (23%) is that the property is located adjacent to a watercourse such that there is a protective covenant. The percentage of hard surface has increased by ~50% due to the doubling of the building footprint.
THE IMPACT ON RUNOFF VOLUMES DUE TO THE COMBINATION OF A REDUCED TREE CANOPY AND A LARGER HOUSE is illustrated by the volume comparison below. The yellow bar on the left represents total annual rainfall. The increase in annual surface runoff volume is a dramatic 59%. Without the tree covenant, the increase would be an even more dramatic 88%. According to Richard Boase, “a key message is that we were doing better 50 years ago when we did not even think about the need for source controls.”
THE BENEFITS OF INCORPORATING LANDSCAPE-BASED SOURCE CONTROLS TO CAPTURE RAIN WHERE IT FALLS is illustrated by the comparisons shown below. This demonstrates that the addition of absorptive landscaping, pervious surfaces and a rain garden would reduce the annual runoff volume to a level below that for the older property.