Rainwater Management in British Columbia: Performance Target Methodology at heart of Provincial Guidebook



A Common Sense, Effective and Affordable Approach

Founded on British Columbia case study experience, and published by the BC Ministry of Water, Land and Air Protection in 2002, Stormwater Planning: A Guidebook for British Columbia formalized a science-based understanding to set performance targets for reducing rainwater runoff volumes and rates. These targets represent the synthesis of biological and hydrological understanding.

Different audiences have different information needs

The Guidebook is structured to meet the information needs of different audiences: from senior managers and elected officials…to those professional planning and engineering staff who are tasked with implementing early action…to land developers and the consulting community. To provide for this range of audiences, the Guidebook is organized in three parts:

  • Part A – The Problem and Principles (‘Why’):written for senior managers, elected officials and those wanting a general introduction to integrated rainwater management.
  • Part B – The Solutions (‘What’):written mainly for engineers and planners, this part provides examples of how to achieve integrated rainwater management at both planning and site levels.
  • Part C – The Process (‘How’): written for administrators and the complete range of stakeholders who will be involved in making the move from planning to action, this part defines roles, methods, means and timing for integrated rainwater management.

For readers who are new to integrated rainwater management, Part A is required reading.

Readers looking for a sense of what integrated rainwater management means on the ground willenjoy the examples in Part B.

Those wanting to start or fund an integrated rainwater management plan or program will find organizational advice in Part C.

Founded on case study experience

The Guidebook draws heavily on case study experience by leading local governments and developers in British Columbia. The illustrations were adapted from projects by the authors.

The overall objective of the Guidebook is to offer a common sense, effective and affordable approach to integrated rainwater management.


Land Development and Watershed Protection can be Compatible

“The widespread changes in thinking about rainwater runoff impacts that began in the late 1990s reflected new insights in two areas: hydrology; and aquatic ecology. These new insights were the result of improved understanding of the causes-and-effects of changes in hydrology brought about by urban development, and the consequences for aquatic ecology,” explains Peter Law, Chair of the Guidebook Steering Committee.

“The missing link between Policy Objectives and Site Design Practices had been a Science-Based Understanding of development impacts. The initial breakthrough in filling this knowledge-gap was achieved in Washington State when Rich Horner and Chris May published their landmark findings in 1997 on the relationships between watershed imperviousness and biological impacts.”

“The next breakthrough was in British Columbia with the development of the Water Balance Methodology in 2000. Through a science-based understanding of the relationship between hydrology and aquatic ecology, it is possible to derive a comprehensive set of watershed protection objectives.”



The Integrated Strategy for Managing the Rainfall Spectrum

The Guidebook formalized the Integrated Strategy for Managing the Complete Spectrum of Rainfall Events as the foundation for a “design with nature” approach to rainfall capture and runoff control. The key to implementing the strategy is that most of the annual rain volume falls as light showers. Although daily rainfall amounts range from light showers to heavy rain to extreme storms, only a handful of long duration downpours occur in any year and extreme events are rare. The Integrated Strategy is illustrated by the graphic below.

To accomplish multiple outcomes, the volume target for development sites is to limit the annual runoff to 10% of annual rainfall. Analysis of  rainfall patterns shows that 90% rainfall capture is typically within reach. In assessing the achievability of 50-year plans for watershed retrofits, however, the focus is on what is feasible and affordable over time.

Integrated Strategy for Managing the Rainfall Spectrum & Mimicking the Water Balance

Design with Nature to Achieve Two Goals

At the site level, a “design with nature” strategy optimizes the use of soil, plants and trees, and surface treatments to capture rain where it falls. Recognizing that there is a practical limit to what can be achieved at the site scale once land clearing has altered the water balance, the integrated strategy for managing the complete rainfall spectrum has three tiered or cascading components. As shown in the accompanying graphic, these correspond to three scales — site, neighbourhood and watershed — to achieve two goals:

  • Protect aquatic habitat through site and neighbourhood solutions that keep rain on site and delay runoff, respectively.
  • Protect life and property through watershed-scale solutions that reduce flooding.

When landscape-based solutions are implemented at the site level, success is evident at the neighbourhood and watershed scales.


Posted August 2006