Changing the Nature of Storm Water Management

Managing storm water through site planning and architecture – the time is now.

Authors:  Ronald P. Schwenger, Principal Architek SBP Inc.
and Steve Williams, Environmental Manager ABT Inc.

With climate change on everyone’s mind these days, progressive, forward-thinking municipal planners and bylaw writers have started looking much closer at water management at the project site level rather than just focusing on an infrastructure approach to urban water management. Increased flash floods in north American cities, coupled by longer periods of drought un summer months, has made managing seasonal water a priority. Fortunately, there are excellent options using innovative new technologies that will make site water management easier to design and implement. This article will highlight some of the new approaches that architects, and builders can utilize to meet the more stringent site water bylaws.

Why Site Water Management Now?

A 2017 report from the Munk School of Global Affairs has sited that flooding is far costlier than fire to homeowners and building owners in Urban Canada. It is estimated that over 2 million households and buildings are very high risk of flooding with costs projected to exceed $650 million dollars annually.

Contrarily, summer months often see longer periods of drought leading to greater and greater levels of water use restrictions in particular for landscaping purposes. This trend shows no signs of letting up over the next coming years. Municipal planners and infrastructure managers realize this and concede that they do not have the capacity or the budgets to perpetually increase infrastructure spending in an attempt to manage the ever-increasing storm water management burden. So municipal leaders are pushing back at the design and development industry with stricter site water management criteria with hard storm water retention and water conservation metrics than ever seen in history.
Architects, landscape architects and builders must now look to tradition methods along with new engineered product innovations pertaining to storm water mitigation and water capture or conservation to meet these increased metric demands from the municipalities.

Green roofs, high performance storm water capture systems – both traditional and new technology, permeable hard-scaping, onsite rainwater harvesting and passive irrigation systems deigned to work in an integrated fashion provide for the site water management solutions that are need this new era. The next chapter will go into more detail about these water management tools and options.

New Innovations and Integrated Solutions

There has been such a dramatic increase in requirements for Low Impact Development and creating sustainable environmental conditions that engineers, architects, developers and manufacturers have been creating new technologies that can benefit society, and development, in conjunction with one and other. However, there is also the municipal perspective where funds are tight and understanding the value created as well as the return on investment becomes front of mind.

That has led to not only new technology but also new design methodology. What do we mean by that?

Well let’s look at innovative methodology and how we can combine that with technology to achieve environmental sustainability utilizing stormwater.

If you could take all the stormwater that traditionally runs off a site into pipes and utilize that water to provide benefits such as lowering the urban heat island effect, providing evapotranspiration to cool ambient temperatures thereby lowering the temperature of asphalt to cool stormwater discharging into tributaries, mitigate the effects of carbon by sequestering as much as we can, recharge groundwater aquifers and utilize the water to provide passive irrigation. Even gray water scenarios to flush toilets etc are very beneficial.

These are all important components to provide environmental benefits to society and create value for cities and developers.

The new methodology comes into play when the use of the stormwater for these areas is to catch, treat it, store it and reuse it! That means catching it on the roof and keeping it on the roof. If we can catch, keep it, and use it on the roof. The water becomes an asset not a liability. Now only in extreme events will water move off the roof and into the infrastructure system.

If we can infiltrate and recharge aquifers, we are using that water to provide a benefit. If we can turn every impervious area into a pervious area we can solve many problems for designers.

What if you could take all that stormwater and send it your trees or send it under green space and use it.

So, what is the value provided?… You need to keep stormwater shallow to access it, and use it. For the municipality, none of that water is going into their pipes, it’s all pretreated so they don’t need to have additional treatment cost. For designers and developers, they don’t need ponds, they get valuable land back and that land can provide even more environmental benefits. Building owners get buildings with lower operating costs, healthier exterior green space and potentially credits for reducing water usage as well as discharge rates. Municipalities don’t have to dig up roads and put bigger and bigger pipes in the ground.

One of the newest technological product advancements is Permavoid. Manufactured by Advanced Building Technologies. Permavoid is actually patented as a sub-base allowing for installation directly under impervious areas. The system is multifunctional. It has extreme loading capability, stores water, conveys water, can infiltrate water and with a membrane can provide passive irrigation as well.

You can take all the stormwater off a parking lot, put it underneath the parking lot and provide environmental sustainability. Permavoid can be used for tree pits, bioswales, bioretention systems, and under permeable pavements.

Permeable Subbase Systems:       

Structural / permeable subbase systems like Permavoid work to reduce the effective impervious behavior of a site in much the same way as any permeable surface with many potential enhancements.
First, water management subbases aim to control sediment transport through source control and pretreatment.  This can dramatically reduce the frequency, labor and maintenance costs associated with typical permeable surfaces.  Second, by routing surface flows through shallow pretreatment systems (ABT-FirstFlush, Bioswales, Raingardens, etc.) it offers the ability to begin filtering out pollutants such as hydrocarbons, heavy metals and more.  This aids in protecting the quality of our groundwater by filtering out pollutants prior to infiltration.  Finally, systems such as this maximize water storage through extremely high void space.  Compared with traditional drainage stone, it can mean up to three times more water storage for a given depth or significantly reduced site excavation requirements.  Whether through permeable surfaces or innovative permeable subbases, increased infiltration on project sites and within our urban spaces is a critical first step to promoting the natural water cycle and ultimately in protecting our fresh water.

Fullerton, CA – Uses a permeable subbase to enhance detention volumes, promote infiltration & protect California’s water.

Connected Blue→
Green Roofs:   

Connected blue→green roofs were developed with one simple idea in mind.  Take all of the water management benefits attributed to blue roofs and use them to overcome the shortcomings of green roofs.
Traditionally, green roofs used very shallow growing media to prevent excessive building loads but with the desire for more native and diverse vegetation, so increased the need for available water.  Logically, more soil was seen as the straightforward solution.  While successful, returns were small, with great cost in structural loads.  The Permavoid blue→green roof overcomes this concern through a lightweight structure with extremely high void space that makes stored water available through wicking cylinders and natural capillary action.  This means huge volumes of water are available to vegetation without the need for pumps, sprinklers, drinking water and energy.  Successfully converting stormwater into a resource in this way adds many important benefits including:

  • Protect our drinking water
  • Prevent CSO’s
  • Reduce flood risk
  • Mitigate the urban heat island
  • Support native/diverse vegetation
  • Increase biodiversity
Amsterdam, NL – Smartroof 2.0 demonstrating the enhanced evaporative cooling potential of connected blue-green roofs

Intregrated Appoach Provides the Best Results:

Applying an integrated approach to site water management will always bring the best results. Combining traditional and blue-green green roofs with high performance storm water catchment systems, rainwater harvesting, permeable hardscapes and smart controls, we can use water very productively for the building and the site.

Sustainable Benefits and Long Term Pay-offs

Site water management provides for many long-term benefits when it comes to sustainable development. Firstly, every time municipal crews dig up existing storm water infrastructure for expansion or repair, it is not only costly from an economic perspective, there is a significant carbon footprint to this activity. With that said, reducing storm water system infrastructure remediation, repair and replacement due to increasing demand has a positive impact on our urban environment.

Additionally, by reducing water use at the site level for landscape irrigation and reusing site retained storm water during wet seasons through traditional or passive irrigation we are not only managing storm water we are conserving water during drier seasons. When we utilize the available new smart technologies for managing water at the site, we dramatically reduce the environmental footprint and save city taxpayers millions of dollars of infrastructure expenditures.

Changing the Nature of Storm Water Management is unquestionably the natural choice moving forward.