Stormwater Management

What is Stormwater?

Stormwater is excess rainfall or melted snow that is not absorbed into the ground and therefore becomes stormwater “runoff”. Over time, as development occurs, paved or built surfaces areas (impervious surfaces) typically increase, reducing the area available to absorb rainfall, thereby generating a greater volume and rate of runoff.

The impacts that development has to our runoff is typically grouped into the three following general categories:

Water Quality

As the runoff travels across these surfaces like roads and parking lots, it picks up pollutants such as gasoline, motor oil, heavy metals, sediment, and solid waste. Runoff from home sites and roofs can contain pathogens, fertilizers and other chemicals. With further development, impervious surfaces may increase, and urbanized areas generate a greater volume of more polluted runoff which is carried to our local creeks and waterways through the stormwater drainage system.

Flooding

Flooding happens when water levels rise above the banks of streams and rivers, sometimes threatening homes or buildings nearby. Development can increase both the amount and rate of runoff, which can increased the potential for flooding to occur.

Erosion

When our streams receive too much runoff from new development, it can lead to excessive erosion along the banks. Streams are constantly adjusting to changes in water flow, so when there’s a sudden increase in flow rate, volume and duration, they naturally “try” to widen to handle the extra flow of water. This widening process often erodes the banks, which can result in impacts to trees, trails or other pieces of infrastructure.

What is Stormwater Management?

Stormwater management reduces the potential impacts caused by uncontrolled runoff by managing the quantity and quality of the water. In natural areas, plants and soil help to absorb rain slowly, filter and break down pollutants, replenish groundwater and keep our waterways healthy. In urban areas, impervious surfaces prevent rainwater from soaking into the ground. Modern approaches to stormwater management try to mimic these natural processes with green infrastructure, in addition to more traditional infrastructure (storm drains) to help protect against the potential for surface flooding.

Traditional infrastructure, often referred to as “grey infrastructure” can include storm drains, which convey runoff to our creeks, waterways or oceans. To combat flooding, stormwater management facilities can be constructed to “hold back” and release runoff to mimic “pre-development” or natural conditions. Stormwater management facilities can include wet ponds, constructed wetlands, dry ponds, underground storage tanks or rooftop storage.

Green infrastructure is often used to treat runoff at the source, by filtering, absorbing and infiltrating smaller levels of rainfall, typically dealing primarily with water quality and erosion, along with flood mitigation effects. Green infrastructure can include rain gardens, bioretention cells, rain barrels, permeable pavement or green roofs.

With a changing climate, more intense rainfall events are expected; therefore, managing stormwater is increasingly more important, in order to reduce peak flows and flooding events.

How Does the Stormwater System Work?

The stormwater system is an integrated network of natural and engineered infrastructure that helps divert, slow and hold excess rainwater, which includes:

  • Catch basins: These are one of the main ways stormwater gets into the underground pipe system. These include metal grates/openings that capture runoff from our roadways and direct runoff to our storm drains.
  • Storm drains: These pipes carry collected runoff away from streets and homes towards our watercourses, creeks and oceans.
  • Watercourses and ditches: Ditches are found in rural areas and act similar to storm drains, where they collect and convey runoff. Watercourses/creeks/streams receive runoff from our storm drains and ditches, where they ultimately discharge to the ocean.
  • Stormwater management facilities: These are human-made basins to manage and treat runoff and release floodwaters at a slower rate to mitigate overwhelming the downstream system. These facilities are typically categorized as follows:
    • Wet ponds: include standing water year-round, where sediments and pollutants are slowed down so they can be deposited.
    • Constructed Wetlands: similar to a wetpond, however, with shallower water and denser plants, providing greater ecological habitat and filtering mechanisms.
    • Dry ponds: depressions/basins with no standing water which are typically grassed, and only fill up with water during rain events.
  • Rain gardens/bioretention cells: hold and filter stormwater before releasing it slowly, removing contaminants and reducing the risk of flooding.
  • Floodplains: flat, vegetated, low-lying areas next to rivers or streams, which have the ability to absorb and filter stormwater; provide extra “storage” of floodwaters, and slow down stream flows to mitigate erosion and flooding.
  • Natural Wetlands: help store and treat excess stormwater and allow for natural infiltration, contaminant removal and aquifer recharge.
  • Outfalls: exit points where stormwater leaves the pipe system and enters waterways or the ocean.
Stormwater Drainage Facts
      • Watercourses and ditches: 536.5 km
      • Stormwater Gravity Mains: 567 km
      • Stormwater Lift Station: 1
      • Stormwater Detention Ponds: 3
      • Rain Gardens: 17

Planning For the Future: Integrated Stormwater Management Plans

Integrated Stormwater Management Plans (ISMPs) examine the linkages between stormwater systems, land use planning and environmental protection. These plans provide a roadmap to meet service objectives while helping communities maintain or improve overall catchment health.

Learn more about our Integrated Stormwater Management Planning.

Stormwater Related Policies, Bylaws and Regulations

Subdivision Bylaw

  • Schedule H includes engineering specifications on the design and installation of storm drains and Schedule F includes standards for stormwater collection systems (including on-site disposal)
  • Section 2.2.18 of the Building and Plumbing Bylaw references the Subdivision Bylaw and other requirements and should be reviewed. 

Stormwater Development Permit

  • The Guideline applies to institutional properties that are increasing impervious surfaces (those that do not absorb water) by 250 m2 or more.

Watercourse and Drainage Bylaw 1996, NO. 7501

  • Regulates and protects watercourses and management of the municipal drainage system

The Streamside Development Permit Area (SDPA)

  • Aims to:
    • protect the land next to streams from new development;
    • restore streamside areas to enhance fish and wildlife habitat.

We all play a Role in Stormwater Management

Green Stormwater Infrastructure

Green stormwater infrastructure (GSI) captures the rain where it falls, mimics natural hydrological processes and uses natural elements such as soil and plants. GSI includes rain gardens, green roofs, bioswales, permeable paving, and other infrastructure that capture, filter, and retain stormwater. This results in reducing the amount of flooding and polluted runoff that reaches our waterways and the ocean.

For additional information and guidance on GSI, here are some useful links:

Natural Assets

Natural assets including forests, watercourses and riparian areas function as green infrastructure and provide stormwater management services such as reduced flooding and improved water quality. Natural assets are one of Saanich’s nine asset types and are included in Saanich’s Asset Management Strategy .

What are we working on?

Visit  Current Projects to learn more about stormwater projects and other Saanich initiatives. 

Other Useful Links and Resources

  1. Provincial stormwater planning guidebook
  2. Partnership for Water Sustainability in B.C.
  3. Center for Watershed Protection — Ellicott City, MD
  4. Low Impact Development Centre
  5. Low Impact Development – Washington Stormwater Center