Beyond the Guidebook 2015: Cowichan Region is applying science-based understanding to restore the ‘Water Balance’ in urbanizing areas

How Performance Targets for Storage, Infiltration and Flow Release are incorporated in a  Rain Garden Design

How Performance Targets for Storage, Infiltration and Flow Release are incorporated in a Rain Garden Design

Restoring the ‘Water Balance’ in Urbanizing Areas

Land development alters the three pathways by which rainfall reaches streams. This changes the proportions of annual Water Balance volumes for surface runoff, groundwater and interflow (lateral flow in shallow soils). Warmer, wetter winters (with less snowpack and more rainfall) and drier, longer summers exacerbate changes in seasonal Water Balance distribution and volumes.

Local government regulates how land is developed, drained and serviced. It has the authority and ability to require that land owners comply with watershed-based volume targets that will restore the Water Balance distribution after land is urbanized.

The Cowichan Region is a provincial leader in demonstrating how to apply science-based understanding and strategies to develop criteria and tools for use in areas where local government action can influence Water Balance outcomes.

To Learn More:

The Cowichan Valley chapter in Beyond the Guidebook 2015 is 14 pages and is organized in six sections. To download a PDF copy and read the complete story, click on Convening for Action in Cowichan Region.

To download a copy of the entire 158-page Beyond the Guidebook 2015, click on this link:

Water Balance Methodology

Primer on Water Balance Methodology_Feb-2014_coverIn 2013, CVRD and the Partnership for Water Sustainability jointly funded a case study to develop a logical and straightforward way to assess potential impacts resulting from urban development; and analytically demonstrate how to restore the hydrologic function of a watershed.

The Cowichan case study is part of the technical foundation for the Primer on the Water Balance Methodology for Protecting Watershed Health.

An integrated design for land development, rainwater management and groundwater recharge would replicate the shallow soil storage and interflow conveyance system in order to mimic the hydrologic performance of a natural watershed.

Performance Targets:

The Primer presents the basic science and a basic knowledge needed to create an understanding of watershed hydrology and the natural processes that affect the flow of rainwater from cloud to stream.

The table beloqw illustrates the application of three Water Balance performance targets to size and design the components of a standard rain garden installation. Targets are watershed-based.



Water Balance Model Express

The key to rainwater management is to connect each property’s hard surfaces with well-designed absorbent or porous surfaces. The Water Balance Model Express for Landowners has pre-set values for the three Water Balance parameters (retention volume, base flow release, and infiltration area). These are established by the local government at a watershed-scale.

The Express guides the property owner through a simple and visually oriented set of sizing options for rain gardens, cisterns, infiltration swales and landscaping.

Rainwater Brochure

The CVRD has developed a ‘rainwater brochure’ to inform and educate the community about core Water Balance concepts, and to support use of the WBM Express.

Act Like a Watershed:

Kate Miiller_2014_120p“Our community is deeply committed to watershed management and stewardship. However, often they are missing the specific tools and information to transform that commitment to concrete actions they can take in their own lives. This often means simple changes to how they develop or care for their properties,” states Kate Miller, Manager, Environmental Services.

D24_Rainwater Brochure