7.3 Stormwater (Rainwater) Management Plans

Another important aspect of water and watershed planning is the management of rainwater or stormwater. All communities in BC are subject to rainfall events and need to provide adequate drainage to prevent localized flooding. It is widely recognized that urban development can increase impervious surfaces, impacting the hydrology of local streams. Rural resource activities such as forestry can also influence land cover, and thus impact, hydrology.

Projections of increased stormwater runoff as a result of climate change and urban development have led some municipalities to seek additional funds for infrastructure upgrades, while other communities are examining alternative approaches to managing rainwater. In addition to, or instead of, building bigger pipes, ditches and pumps to convey water from bigger storms, some communities are taking the approach of “store it, spread it, and sink it”. Rainwater and stormwater can be viewed as a valuable resource that can be stored in wetlands and detention ponds and infiltrated into the ground to recharge water tables. This can reduce or avoid many of the economic and environmental costs associated with the traditional model of conveying rainwater as quickly as possible from roads, rooftops and parking lots into storm sewers, drainage ditches and streams. Urban stormwater runoff can adversely impact stream hydrology, fish habitat and watershed health by eroding stream banks, by causing water turbidity and siltation of spawning and rearing habitat, and by introducing other pollutants, such as oil from roads, into the system.

Under the Local Government Act, municipalities are responsible for the provision of drainage, and in some cases, Regional Districts may also have associated responsibilities. How we handle stormwater has a huge impact on aquatic ecosystems. Integrated stormwater management planning is a proactive process that utilizes land use planning tools to protect property and aquatic habitat from stormwater flows, while at the same time accommodating urban growth. Ideally, the aim of these plans is to ensure that stormwater runoff resembles natural runoff patterns (i.e., volume and timing of surface water runoff), and does not transport pollutants or sediment from the land into watercourses. Stormwater management plans are typically completed at the local government level, with guidance from the Province. 5

BC’s Stormwater Planning Guidebook, released in 2002, is premised on the idea that land development and watershed protection can be compatible. It assumes that municipalities exert control over runoff volume through their land development and infrastructure policies, practices and actions.

Integrated Stormwater Management Plans (ISMPs) are required to be developed and implemented by Metro Vancouver’s member municipalities in accordance with the Integrated Liquid Waste and Resource Management Plan. To help facilitate this, Metro Vancouver developed a comprehensive ISMP Template (consistent with the provincial guide) to guide member municipalities with this process. The updated LWMP is pending approval from the Minister of Environment.

Outdated approaches to stormwater management, which fail to respect natural systems and water cycles, have been accused of being one of the largest water pollution challenges in the province. In recent years, rainwater management has emerged as a new way of thinking about the precipitation that falls on the land. Instead of viewing stormwater as a site-specific problem that is best solved by piping water away from properties into streams, rainwater management considers the dynamics of the entire watershed and identifies how development can use “green infrastructure” to maintain natural systems and protect buildings. Green infrastructure is a concept that emphasizes the importance of the natural environment in decisions about land use planning. For example, the installation of permeable pavements, rain gardens, bioretention ponds and constructed wetlands help reduce the volume of runoff that enters sewer systems and increase absorption. Instead of relying heavily on pipes and concrete, green infrastructure takes advantage of the natural absorption, storage, evaporation and filtration services that nature provides. As opposed to the quick, high-impact flush that comes with traditional approaches to stormwater management, lower impact green development seeks to mimic the natural water cycle by allowing water to infiltrate down through the ground and slowly release into the watershed.i

The release of Beyond the Guidebook: Context for Rainwater Management and Green Infrastructure in British Columbia in 2007 has helped shift the focus of traditional stormwater management to the integrated, holistic approach that rainwater management embodies.

Climate change—and in particular the potential for more frequent and more intense extreme precipitation events—is an important consideration in this type of planning. Urban flooding is now the leading cause of home insurance claims in Canada, and is a priority of the insurance industry. For more details refer to Hazard Perceptions: Public Education Can Help Snap Flooding, from the Institute for Catastrophic Loss Reduction. There is limited science on which to base projections for a specific location; however, some jurisdictions have identified voluntary planning contingencies for extreme precipitation based on the best science available. For example, on Vancouver Island, the Capital Regional District has identified a planning contingency of a 15% increase in frequency and duration of winter storms for the next 100 years. These contingencies should inform decisions about which stormwater management techniques to adopt and what the management goals should be in terms of rate of runoff.

Characteristics, Benefits and Applications

Under the Environmental Management Act (Municipal Sewer Regulation), stormwater management planning is a formal requirement of Liquid Waste Management Plans, which is one of several mechanisms used by the Province to regulate stormwater in BC. Although municipalities are generally not required to have Liquid Waste Management Plans, they often opt to complete such plans because the plans allow a suitable length of time to develop and implement effective and affordable solutions.

The outcome of integrated stormwater planning includes regional or watershed level objectives and priorities, integration of these objectives into community planning, and implementation of on-site practices that reduce volume and rate of run-off and improve water quality. Stormwater management plans need to be integrated with Official Community Plans and zoning bylaws that regulate the location of development and density of use. 5

Some benefits of undertaking stormwater management planning and implementing completed plans include:

• protection of the aquatic environment, including water quality and stream flow, and protection from flooding;
• protection of community assets and infrastructure from localized flooding;
• protection of water supply (e.g., groundwater recharge areas);
• management of erosion and sedimentation processes; and
• protection of aesthetic values and recreational uses of water.

Key Elements and Steps

The Stormwater Planning Guidebook provides a detailed explanation of the various stages of preparing a plan. It outlines three key steps and associated methods that work towards integrated stormwater management solutions, and five guiding principles to uphold in the process, as outlined below. They include the following:

Stormwater Planning Steps

1. identify at-risk catchments;
2. set preliminary performance targets; and,
3. select appropriate stormwater management site design solutions.

Guiding Principles of Integrated Stormwater Management (ADAPT)

1. Agree that stormwater is a resource;
2. Design for a complete spectrum of rainfall events;
3. Act on a priority basis in at-risk catchments;
4. Plan at four scales (regional, watershed, neighbourhood and site); and,
5. Test solutions and reduce costs by adaptive management.