Capture Rain Where It Falls: At 2007 Water Balance Model Partners Forum, Ministry of Environment's Peter Law provided historical context for Performance Target Methodology
Note to Reader:
The Water Balance Model is the centrepiece of the Water Sustainability Action Plan for British Columbia. In March 2007, the Inter-Governmental Partnership held a Water Balance Model Partners Forum so that local government partners could share success stories and lessons learned in implementing green infrastructure.
Integrated Strategy for Managing the Rainfall Spectrum & Mimicking the Water Balance
Test the Achieveability of Water Balance Performance Targets
The desire to mitigate environmental impacts has provided a driver for the ‘green infrastructure’ movement in British Columbia. This movement is water-centric, is founded on a natural systems approach, and is influencing infrastructure policies, practices and standards.
Water Balance Methodology
Development of the Water Balance Methodology for establishing Performance Targets has facilitated implementation of an Integrated Strategy for managing the complete rainfall spectrum to achieve green infrastructure and water-centric outcomes.
Stormwater Planning: A Guidebook for British Columbia pioneered the application of performance targets to rainwater management, and the Water Balance Model enables users to test their achievability.
For a performance target to be implemented and effective, it must be quantifiable. It must also have a feedback loop so that adjustments and course corrections can be made over time. To be understood and effective, a performance target needs to synthesize complexity into a single number that is simple to understand and achieve, yet is comprehensive in scope.
A runoff volume-based performance target fulfills these criteria.
Effective and Affordable
As explained by Peter Law, who was Guidebook Chair while on the staff of the Ministry of Environment, “When we wrote the Guidebook, we recognized there is a material difference in the characterization of surface runoff that originates from an individual development site versus flow that you see at a catchment or watershed scale. What you see in a watercourse is the total flow – that is, water that flows overland plus water that moves through soil until it daylights.”
“This is one reason why Chapter 6 in the Guidebook emphasizes the need for flexibility in setting performance targets, and states that performance targets should be customized for individual watersheds and catchments, based on what is effective and affordable in the context of watershed-specific conditions.”
To Learn More:
To download a copy of Chapter 6, click on Setting Performance Targets and Design Guidelines.
Surface Runoff versus Total Flow
“The output from the current version of the Water Balance Model is ‘surface runoff’, whereas the output from the Water Balance Model powered by QUALHYMO will be ‘total flow’. This expanded capability is a key to determining what level of rainfall capture may be effective and affordable,” stated Jim Dumont, Engineering Applications Authority for the Water Balance Model Partnership.
“It is important for everyone to keep in mind that the application of a performance target approach is essentially about due diligence and doing the right things to capture rain where it falls. The performance target approach is intended to be the exact opposite of a prescriptive approach. The latter is counter-productive when it leads to rigid standards that have the effect of inhibiting creativity and innovation”, added Peter Law.
