Stormwater Basins

A common method to manage stormwater runoff is through stormwater basins or ponds, which collect and release runoff at a controlled rate to avoid flooding or erosion of downstream areas. Stormwater basins can either be detention basins, which are dry between storms, or retention basins, which have a permanent pool of water. Detention basins only contain water after a rain event, while retention basins always hold water.

The Canada Games Centre on Lacewood Drive in Halifax has an underground detention basin on-site that collects stormwater runoff from the building’s roof, parking lot and lawn area. Underneath a field beside the Centre lies a 10m deep hole that is filled with rock. Large, boulder size rocks were used to increase infiltration. Two metres beneath the surface lies a perforated pipe that runs across the length of the field and catches any overflow. During a heavy precipitation event, water enters the dry detention pond and infiltrates the rock layer. Water only enters the perforated pipe if the water level rises to 2 metres below the surface, and Jeff Pinhey, the site engineer has never witnessed an overflow event. The detention pond was built during the construction of the building. 

Underground detention pond at the Canada Games Centre

Underground detention ponds are safe, do not need to be fenced and provide additional space for on-site recreation. Detention ponds can also be above ground, such as this example in Dartmouth Crossing. We’ll explore wet retention ponds in more detail in future posts.

Above-ground dry detention pond in Dartmouth Crossing

Bioswales

The Prospect Road Community Centre was built in 2010 with several stormwater features  incorporated into the building's design. Runoff from the roof is collected in a large underground cistern and reused in the building for non-potable uses such as flushing toilets.

Runoff from the site and parking lot are collected in bioswales, which are vegetated depressions where water collects and soaks into the ground. This filtration improves water quality by removing pollutants and allows for water to re-enter the ground, recharging groundwater supply.

Water enters the bioswale through curb openings

The bioswales are composed of an underground perforated pipe surrounded by 5 feet of rock and gravel. During an extreme precipitation event, high volumes of water flow overland into the bioswales, flooding the rock area and overflowing into the perforated pipe. The water is then collected and piped off-site, ultimately draining into a natural wetland adjacent to the building. 

 Bioswales reduce strain on built stormwater systems and reduce likelihood of flooding and infrastructure damage by passively allowing water to move off-site. This engineered system mimics how water would naturally flow in an unaltered environment. Bioswales are not only useful, but also can be an attractive landscape feature.

Water drains off-site into a natural wetland

Stormwater Infiltration and Inflow

In HRM, there are two types of wastewater collection systems. Separated wastewater systems are designed to carry wastewater only. In older areas of Halifax and Dartmouth, combined systems exist that accept both wastewater and stormwater. When stormwater unnecessarily enters the wastewater system, the excess water load can cause a range of problems.

Stormwater can enter the wastewater system in two ways:

Infiltration (groundwater entering through cracks and leaks in the wastewater pipes) or Inflow (stormwater entering the system through a direct connection like sump pumps, drains or catchbasins).  Stormwater that enters the wastewater system ends up being collected and treated unnecessarily, which causes extra strain on  treatment plants and can lead to  combine sewer overflows (CSO) in heavy rains. CSOs cause untreated wastewater to overflow directly into natural water bodies leading to environmental and health risks. Infiltration and inflow can also cause sewer backups in people’s homes and can add to operating costs of treatment facilities which ultimately leads to higher rates for customer.  To address this serious issue, stormwater needs to be better managed at the source, by retaining runoff (allowing it to soak into the ground, or be collected and reused) on-site instead of allowing it to enter the wastewater system.

To reduce the frequency and magnitude of infiltration and inflow events,  Halifax Water has designed a Stormwater Inflow Reduction (SIR) Program to help customers indentify ways to better manage stormwater on their properties. The number one tip for property owners? Disconnect your downspout if it is directly connected to the wastewater system. This water can be redirected onto your lawn and collected in a rain garden or rain barrel, or allowed to directly soak into the ground.


If you have concerns about where your water is going, you can call 490-RAIN (7246) to have a free inspection of your property. Click here to find out more.

Managing Stormwater Quality in Urban Lakes

Stormwater runoff can have serious impacts on the water quality of urban lakes and other receiving water bodies. An innovative technique called Contaminant/Sediment Control (CSC) Filter Systems has been shown to greatly improve water quality by removing stormwater pollutants before they drain into the natural system. These filters have been placed at stormwater outfalls around First Lake in Lower Sackville, Nova Scotia, which has led to significant improvements in the lake's water quality. Check out our latest video, featuring Larry Bell of W.A.T.E.R Research Associates, to see the filters in action!

Bioretention and Rainwater Harvesting

Improving stormwater in urban and rural areas helps to protect the health of rivers, streams and lakes.  Improvements made to an existing building or parking lot are known as a retrofit.  The Ecology Action Centre is currently considering sites within the city of Halifax for a potential stormwater retrofit project.  Learning from retrofit projects in other cities is helpful for developping options for a site in Halifax.


The short video below demonstrates two types of retrofits: a bioretention pond that captures and treats runoff from a large parking lot and rainwater harvested off a roof that is used for irrigating a sportsfield.

Grey water and black water recylcing

Check out our first interview with Shawn Wilkie of Grun-Sol Technologies explaining the basics of grey water and black water recycling. Recycling water is an efficient way to conserve water, save costs and alleviate some of the strain on wastewater systems.

Low Impact Development

Low Impact Development (LID) is an innovative stormwater management approach that aims to replicate a site's predevelopment hydrology by using simple design techniques that impacts of runoff while having a low impact on the environment. LID are cost-effective, site-level BMPs that address runoff close to the source and improve human health, enhance habitat and save municipalities, contractors, developers and homeowners money. Some common examples include downspout disconnection, vegetation plantings and preservation, raingardens, cisterns and sidewalk storage (if you are not familiar with all of these tools, don’t worry, we’ll cover them in upcoming posts!). The LID concept came out of Prince George County, Maryland in the mid 1980’s as a way to address growing environmental and economic costs of urban stormwater runoff. The following objectives and principles come from Maryland’s Department of Environmental Resources Programs and Planning Division document Low-Impact Development Design Strategies: An Integrated Design Approach.

Green Roof at Dalhousie University

LID Runoff Control Objectives:

• minimize disturbance
• preserve and recreate natural landscape features
• reduce effective impervious cover
• increase hydrologic disconnects
• increase drainage flow paths
• enhance off-line storage
• facilitate detention and infiltration opportunities

The Principles of LID are to:

• integrate stormwater management early in site planning activities
• use natural hydrologic functions as the integrating framework
• focus on prevention rather than mitigation
• emphasize simple, nonstructural, low-tech, and low cost methods
• manage as close to the source as possible
• distribute small-scale practices throughout the landscape
• rely on natural features and processes
• create a multifunctional landscape

Stormwater BMPs

The increase in stormwater runoff velocity and volume caused by a high impervious surface cover in urban areas can lead to decreased water quality, increased erosion and damage to homes and infrastructure. Climate change is expected to bring about more frequent and intense precipitation events which will only escalate the problems. So what can be done?

Around the world cities and towns are implementing a range of stormwater best management practices (BMPs) which are control measures to mitigate quality and quantity of runoff. BMPs can be source control measures which are installed on-site, conveyance control measures which manage runoff between the source and output (ie, in sewers and ditches), end of pipe measures which provide mitigation at the end of the conveyance system and general BMPs such as public education and policy development. Specific examples include:

Source controls - rain barrel, porous pavement, green roof, rain garden, lot grading.

Conveyance controls – vegetated swales, pervious pipe systems

End of pipe controls- constructed wetlands, detention/retention facilities, buffer strips

Many of these methods are already being used in Halifax. We will explore each of these tools in more detail to understand how they work and when they should be used. If you can’t wait and need more information now, check out HRM Stormwater Management Guidelines for a detailed description of stormwater BMPs.

Permeable pavers are a great alternative to concrete driveways and parking lots

What is stormwater?

 

Stormwater is rainwater and melted snow that runs off roads, lawns, roofs and other hard surfaces. In natural systems, when stormwater is absorbed into the ground, it is filtered and flows into streams, rivers and coastal waters or recharges groundwater. In urban areas, impervious surfaces reduce water retention and infiltration. Instead, water runs rapidly over these hard surfaces, collecting pollutants along the way, and flows into storm drains and sewer systems. Urban runoff can contain fertilizers, oil, dirt, garbage and other contaminants, which impacts water quality in the receiving water bodies. In areas with combined storm and waste water sewers, the combined system can become overloaded and lead to untreated sewage being directly released. Stormwater runoff is not only harmful to aquatic habitat and species, but can also impact human health, increase erosion and flooding and cause damage to infrastructure and property.

From http://www.learnnc.org/lp/editions/mudcreek/6394

 

Changes in the amounts and intensity of precipitation events associated with climate change along with aging infrastructure and an expanding area of impervious surfaces in most cities make managing stormwater a critical issue. In the coming months, we will be exploring alternative solutions for homeowners, contractors and municipalities to effectively manage stormwater and we will be sharing what we learn along the way on this blog.

Over the summer of 2012, we will be retrofitting an existing building in Halifax with a range of stormwater best management practices (BMPs) to showcase how different tools can retain water and reduce the amount of stormwater runoff entering our sewage system. We will be documenting the stormwater retrofit every step of the way, and updating this site regularly with photos, videos. We encourage you to share your thoughts, concerns, and experiences with us, so we can learn from each other and address these issues together.

Keep checking in for updates.