Risk management for public entities: Stormwater management safety measures

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Stormwater management (SWM) ponds are manmade facilities designed to manage the runoff from rainfall and snowmelt and have become an essential measure in maintaining the natural hydrologic cycle. Municipalities have been increasingly using SWM ponds as a way to reduce pollution, remove sediment particles, return clean water to waterways, and provide flood protection.

When planning to construct SWM ponds, municipalities need to consider the public safety risks associated with its development and maintenance, and the safety design measures they need to implement to prevent, mitigate, and/or transfer the risks and liabilities they may encounter. Similar to other municipal-owned and maintained properties, municipalities bear the responsibility of installing the appropriate physical and safety measures aimed to prevent trespassing, vandalism, injury, and/or death at these sites. As part of an integrated approach, municipalities will need to implement a series of measures addressing the following areas:

  • Environmental (for example, topography and pond design)
  • Social (for example, public consultation) 
  • Economic (for example, retrofitting and maintenance costs
  • Safety (for example, physical measures and public awareness)

A commonly discussed safety measure is the appropriate manner to deter unauthorized access to SWM ponds. The following guidance provides an overview on the risks and benefits of installing a full perimeter fence, as well as alternative solutions.

Perimeter fencing 

Traditionally, perimeter fencing has been used as the primary measure to deter unauthorized access to SMW ponds and any related equipment, thereby reducing the likelihood of injury (such as slips, trips, or falls) or death (for example, from drowning). This fencing needs to comply with municipal requirements (including minimum height, security, scalability, vandal-resistance, attractiveness, and durability) and is often informed by pond design features, such as the pond slope, pond depth, and pond high water level. Although installing a full perimeter fence around SWM ponds poses clear public safety benefits, it also introduces other downstream risks and implications for the public entity, including:

  • Potentially limits emergency response: If an individual accesses the SWM pond by scaling the fence and subsequently suffers injury or falls into the pond, the fence may pose an obstacle for emergency responders that would delay their timely attendance and rescue.
  • Limits maintenance activity: If maintenance activity requires the use of large equipment, the fence may limit access to the area, which could then necessitate the temporary removal of portions of the fence.
  • Timely demand maintenance: In the event the fence sustains damage from weather events, vandalism, or other factors, it will require timely identification and repair to maintain security of the site and reduce potential liability. 

Due to such risks, some municipalities have discouraged the installation of fencing around the entire perimeter and have minimized its use to targeted areas, while others have limited the installation of fencing around the entire perimeter of SWM ponds to only those that meet certain specifications.

Alternative solutions

Instead of complete perimeter fencing, or in addition to it, municipalities may employ alternative approaches to help ensure public safety. The layered implementation of targeted safety measures can help reduce the likelihood of a sustained injury or death resulting from unauthorized access to the SWM pond.

  • Partial fencing or guard rails: In some areas, fencing will be the most effective method to deter access. Install partial fencing and/or guardrails as required, specifically where vertical walls or steep slopes are present in the design structure of the SWM pond.
  • Perimeter vegetation: Thoughtful landscape design can be used instead of and/or in addition to traditional perimeter fencing to deter access to the pond area, steep slopes, and other areas that are deemed hazardous. Plant the vegetation based on the landscaping zone at each of the different components of the SWM, which includes the inlet, forebay, pond, and outlet. 
  • Safety signage: Public signage identifies the area as a stormwater management site and raises public awareness of potential hazards of the site. Install signs at locations that are highly visible to the public, including entrances to the site or maintenance access routes.
  • Integrated gradual pond slope: Incorporating gradual slopes in the pond design can help reduce the likelihood of injury or death, as they make it less likely that individuals will fall into the pond and easier for them to escape if they do. Typically, guidance recommends that the slope not be steeper than one foot vertical for each four feet horizontal coverage.

All proposed safety measures and design choices should be verified to be in line with the requirements set out by each public entity and other authorities having jurisdiction.

Summary 

While there are clear public safety benefits to installing full perimeter fencing around SMW ponds, such as preventing unauthorized access and reducing likelihood of injury or death, it introduces other downstream risks and implications. As an alternative, or in addition to, full perimeter fencing, municipalities may consider other safety measures. Through a layered implementation of targeted safety measures, municipalities may help lessen their risks and protect their community.