Respecting Stormwater Management Standards for Development Activities

The City of Halifax, in conjunction with municipal utility Halifax Water, passed a reformed stormwater management guideline in 2020 that helps to address flooding and other problems in the city. A coastal city on the Eastern side of Nova Scotia, Halifax is no stranger to flooding. In addition to the heavy precipitation events that routinely affect most of Canada, Halifax also has to worry about Hurricanes, tropical storms, and sea level rise. All of these factors will only be exacerbated by the effects of a changing climate. While Halifax has had development protocols in place to help reduce the overland runoff of water for many years, this most recent iteration has incorporated some of the most up-to-date thinking on the issue of preventing flooding through urban design and has specifically sought to enforce the retention of water onsite, often through the use of ‘green infrastructure.’

Understanding and Assessing Impacts

Stormwater is water from groundwater discharge, surface water, precipitation or melting snow and ice that flows across the landscape. Stormwater flows across a property (from rooftops, paved areas, graveled areas, bare soil, lawns, etc.) and gathers along streets, drains, open channels, and sewers in increasingly large amounts, until it eventually discharges into water bodies. In areas served by combined sewer systems, stormwater flows with wastewater to a wastewater treatment facility, where it may lead to a combined sewer overflow. As areas continue to urbanize, stormwater management is especially important due to decreases in natural surfaces and the increases of impervious surfaces like rooftops, sidewalks and asphalt. These surfaces compound the issues with stormwater because they change the permeability of the landscape, preventing stormwater from infiltrating into the ground. Stormwater can pick up and carry pollutants (oil, grease, chemicals, dirt, sediment, nutrients, and pathogens). Without treatment, these pollutants can have a significant impact on downstream watersheds. Stormwater pollution can be significantly reduced with the use of applicable best management practices. A properly designed and functioning stormwater system conveys the stormwater without damage to property, harm to personal health, significant inconvenience to the public, or detrimental environmental effects. However, some recent and historical storm events have caused damage and inconvenience to both public and private property. These storm events have caused problems that generally fall into the following categories: private property flooding, flooding and icing in the public right-of-way, sewer system backups, excessive stormwater in the wastewater system, and degradation in receiving water quality. Scientific evidence indicates that climate change has already contributed to an increase in the severity and frequency of storm events and will continue to do so. There is growing evidence to suggest that regulating site design features to promote control of stormwater at the source is more effective than public infrastructure at lessening effects.

Identifying Actions

The Halifax Regional Municipality (HRM, Halifax) spans a geographic area of 5,600 square kilometres and has a population of approximately 400,000. Halifax was formed in 1996 through the amalgamation of four pre-existing municipalities. The amalgamation resulted in the inheritance of various policies and procedures relating to stormwater management (SWM). In 2007 HRM conveyed the municipal wastewater and stormwater sewer systems, including ditches inside the service boundary, to the Halifax Regional Water Commission (Halifax Water). Since this time, there has been an increased awareness of the benefits of improving stormwater quality. Before the adoption of this document, the stormwater management design requirement, adopted in 2002, was to balance pre-development flow with post-development flow over a development site. This requirement is based on the quantity, by limiting the stormwater flow rate leaving an overall site during prescribed precipitation events. However, it does not consider water quality impacts, nor does it manage stormwater throughout the site itself, but focuses on the ultimate outlet of the site. The Integrated Stormwater Management Policy Framework (ISMPF) was developed between HRM and Halifax Water and adopted by HRM Regional Council and the Halifax Water Board in January 2018. This document was developed between HRM and Halifax Water to support and implement the ISMPF by providing direction for mitigating the long-term impacts of development on natural water bodies and downstream properties.

Implementation

The Hierarchy Approach was adopted as part of the guiding principles used in establishing the objectives for this document. The applicant shall demonstrate that the Stormwater Management Plan for the proposed development implements the hierarchy approach within the private stormwater management of the development site, described as follows.

  1. Source Control practices retain stormwater where it reaches the site (i.e. retain rain where it falls). Source controls at the lot level are the preferred method for controlling the impacts of stormwater.
  2. Conveyance Control such as private vegetation swales and/or infiltration systems, can limit the flow as it moves across the site.
  3. End-of-Pipe Control, considered the last treatment opportunity prior to leaving the sites, shall be implemented if source and conveyance controls are unable to achieve the necessary level of stormwater quality and quantity control targets.

Engineered solutions such as “grey infrastructure” will be considered if the above methods are unable to achieve the targets alone. These practices often require more ongoing maintenance than BMPs, and do not have the added benefits that vegetated “green” infrastructure offers. Implementing the hierarchy approach on private development sites improves the overall downstream stormwater quality above and beyond the traditional approach of an end-of-pipe stormwater management facility. The use of stormwater BMPs upstream will decrease the requirements for end-of-pipe facilities. In general, end-of-pipe facilities are the least preferred approach, because of the construction and maintenance costs, and the potential disruption of land features. For these reasons, stormwater BMPs typically result in better Return on Investment results.

Resources


Understanding and Assessing Impacts

Stormwater is water from groundwater discharge, surface water, precipitation or melting snow and ice that flows across the landscape. Stormwater flows across a property (from rooftops, paved areas, graveled areas, bare soil, lawns, etc.) and gathers along streets, drains, open channels, and sewers in increasingly large amounts, until it eventually discharges into water bodies. In areas served by combined sewer systems, stormwater flows with wastewater to a wastewater treatment facility, where it may lead to a combined sewer overflow. As areas continue to urbanize, stormwater management is especially important due to decreases in natural surfaces and the increases of impervious surfaces like rooftops, sidewalks and asphalt. These surfaces compound the issues with stormwater because they change the permeability of the landscape, preventing stormwater from infiltrating into the ground. Stormwater can pick up and carry pollutants (oil, grease, chemicals, dirt, sediment, nutrients, and pathogens). Without treatment, these pollutants can have a significant impact on downstream watersheds. Stormwater pollution can be significantly reduced with the use of applicable best management practices. A properly designed and functioning stormwater system conveys the stormwater without damage to property, harm to personal health, significant inconvenience to the public, or detrimental environmental effects. However, some recent and historical storm events have caused damage and inconvenience to both public and private property. These storm events have caused problems that generally fall into the following categories: private property flooding, flooding and icing in the public right-of-way, sewer system backups, excessive stormwater in the wastewater system, and degradation in receiving water quality. Scientific evidence indicates that climate change has already contributed to an increase in the severity and frequency of storm events and will continue to do so. There is growing evidence to suggest that regulating site design features to promote control of stormwater at the source is more effective than public infrastructure at lessening effects.

Identifying Actions

The Halifax Regional Municipality (HRM, Halifax) spans a geographic area of 5,600 square kilometres and has a population of approximately 400,000. Halifax was formed in 1996 through the amalgamation of four pre-existing municipalities. The amalgamation resulted in the inheritance of various policies and procedures relating to stormwater management (SWM). In 2007 HRM conveyed the municipal wastewater and stormwater sewer systems, including ditches inside the service boundary, to the Halifax Regional Water Commission (Halifax Water). Since this time, there has been an increased awareness of the benefits of improving stormwater quality. Before the adoption of this document, the stormwater management design requirement, adopted in 2002, was to balance pre-development flow with post-development flow over a development site. This requirement is based on the quantity, by limiting the stormwater flow rate leaving an overall site during prescribed precipitation events. However, it does not consider water quality impacts, nor does it manage stormwater throughout the site itself, but focuses on the ultimate outlet of the site. The Integrated Stormwater Management Policy Framework (ISMPF) was developed between HRM and Halifax Water and adopted by HRM Regional Council and the Halifax Water Board in January 2018. This document was developed between HRM and Halifax Water to support and implement the ISMPF by providing direction for mitigating the long-term impacts of development on natural water bodies and downstream properties.

Implementation

The Hierarchy Approach was adopted as part of the guiding principles used in establishing the objectives for this document. The applicant shall demonstrate that the Stormwater Management Plan for the proposed development implements the hierarchy approach within the private stormwater management of the development site, described as follows.

  1. Source Control practices retain stormwater where it reaches the site (i.e. retain rain where it falls). Source controls at the lot level are the preferred method for controlling the impacts of stormwater.
  2. Conveyance Control such as private vegetation swales and/or infiltration systems, can limit the flow as it moves across the site.
  3. End-of-Pipe Control, considered the last treatment opportunity prior to leaving the sites, shall be implemented if source and conveyance controls are unable to achieve the necessary level of stormwater quality and quantity control targets.

Engineered solutions such as “grey infrastructure” will be considered if the above methods are unable to achieve the targets alone. These practices often require more ongoing maintenance than BMPs, and do not have the added benefits that vegetated “green” infrastructure offers. Implementing the hierarchy approach on private development sites improves the overall downstream stormwater quality above and beyond the traditional approach of an end-of-pipe stormwater management facility. The use of stormwater BMPs upstream will decrease the requirements for end-of-pipe facilities. In general, end-of-pipe facilities are the least preferred approach, because of the construction and maintenance costs, and the potential disruption of land features. For these reasons, stormwater BMPs typically result in better Return on Investment results.

Resources