Whole-System, Water Balance Approach
The Partnership for Water Sustainability in British Columbia collaborates with government and others to develop methodologies, tools and resources to support implementation of the Whole-System, Water Balance Approach; as well as provide teaching, training and mentoring.
Under the umbrella of the Water Sustainability Action Plan for British Columbia, the Partnership is the steward for Stormwater Planning: A Guidebook for British Columbia-PDF. Released in 2002, the Guidebook established a new direction for drainage engineering in British Columbia with introduction of the Integrated Strategy for managing the complete spectrum of rainfall events.
Look at Rainfall Differently
The Integrated Strategy expands the scope and responsibility of drainage practice to include stream health. The Guidebook looked at rainfall differently. Its innovation included:
- Translated science-based understanding.
- Introduced the “retain-detain-convey” strategy.
- Formalized the performance target approach.
- Established an adaptive management precedent.
- Initiated the paradigm-shift to rainwater management.
Building on the Guidebook foundation, the subsequent and ongoing Beyond the Guidebook program delivered by the Partnership is a multi-year process. The program objective is to encourage, enable and support changes to drainage engineering practice so that it is science (evidence)-based.
Water Balance Performance Targets
The Guidebook centrepiece is the Water Balance Methodology. Since 2002, understanding has grown, and so the Partnership has evolved the methodology to downscale performance targets from the regional to site scales. The methodology now interweaves watershed hydrology and stream dynamics.
The Water Balance Methodology recognizes the potential change in the paths followed by rainwater in the hydrologic cycle; and establishes the methodologies required to protect stream and watershed. The flow-duration relationship is the cornerstone of the Water Balance Methodology.
The Partnership collaborates with government to apply the Water Balance Methodology and calculate watershed-specific performance targets. Desired outcomes in implementing performance targets are two-fold: prevent flooding and protect stream health.
Integrated Strategy for Managing the Rainfall Spectrum has 3 Objectives:
- Mimic the proportion of water infiltrated to groundwater under natural watershed conditions;
- Provide interflow connectivity to the stream;
- Maintain or decrease potential flood risks.
British Columbia Guidance Documents:
- Stormwater Planning: A Guidebook for British Columbia
- Beyond the Guidebook 2015
- Beyond the Guidebook 2010
- Beyond the Guidebook 2007
- Beyond the Guidebook Primer Series
- Watershed Case Profile Series
Look at Rainfall Differently:
Watershed protection starts with an understanding of how water gets to a stream, how long it takes, and whether there are impacts along the way.
Flow Path & Time Scale:
There are three flow paths, each with a different time scale:
- Surface – from minutes to hours
- Interflow – from days to seasons
- Deep Groundwater – from years to decades.
In coastal British Columbia, interflow is the primary pathway in a properly functioning watershed system. This is illustrated in the table below.
|Annual Water Balance by Region (as derived from long-term hydrometric data for gauged watersheds)|
|Flow Paths||Coastal BC||Alberta -Edmonton||Ontario – Ottawa||Nova Scotia||Maryland|