Across North America and globally, governments have begun to acknowledge the importance of permeable surfaces.
Most towns and cities now actively incentivize the use of permeable surfaces in new public and private projects, and some have even begun to mandate the use of permeable paving products.
Landscape architects and Parks Department designers have long recognized the need for permeability, but lacked access to affordable and effective permeable paving products.
This has now changed with a wide range of permeable surfaces available, including permeable concrete, permeable asphalt and stabilizing aggregate binders, such as Organic-Lock™.
There is no better example of the push for permeable surfaces than China’s ‘Sponge City’ initiative.
In response to repeated problems of flooding, the Chinese government launched a program to increase the permeability of its urban developments to make their cities act like a ‘sponge’ and reduce the risk of flooding .
Currently in the pilot phase, this program will eventually be rolled out to over 600 Chinese cities and is a cornerstone of the countries efforts to curb flooding .
Other governments, such as Adelaide in Australia have taken notice of this innovative program and begun their own Sponge City programs . US states and municipalities have also introduced a range of subsidies and tax breaks for projects using permeable paving products .
With the right approach to the planning of your next major project, you can decrease its overall environmental impact and save money by choosing the right permeable materials.
Before looking at the finer details of the available incentives, lets quickly review the damage that non permeable surfaces cause and how permeable surfaces can help.
The Importance of Permeable Surfaces
One of the most publicized negatives of impermeable surfaces is the increased chance of flooding.
Impervious surfaces increase runoff velocity far beyond natural levels, causing flooding during large rain events whilst also impacting the ability of aquifers to recharge via infiltration .
The inability of an aquifer to recharge has the converse effect of lowering the level of streams and lakes during times of low rainfall, impacting wildlife. Research suggests even a 20-30% reduction in natural permeability adversely affects groundwater recharge .
Another well documented problem is the buildup of pollutants on impermeable surfaces. Petroleum products, chemicals, fertilizers and other compounds build up on the surface rather than being filtered out .
When it rains, the pollutants immediately enter the stormwater system and the natural environment due to the high runoff rate.
A study conducted by the Maryland Department of Natural Resources shows that a healthy stream full of sensitive species and trout can become devoid of all but the hardiest species of insects due to pollution when just 20% of the watershed covered in impermeable surfaces .
These examples just scratch the surface of the problems associated with impermeable surfaces and highlight the need for the change to permeable paving materials.
Permeable surfaces provide humans with the hard surfaces which we have come to rely upon, without this large impact on the environment. The benefits of permeable paving surfaces include:
- Near natural levels of infiltration, allowing for normal aquifer recharge .
- Limits the velocity of runoff, helping to prevent flooding and relieving stress on stormwater drainage systems .
- Limits the ability of harmful pollutants to enter waterways, protecting sensitive wildlife .
When you consider the environmental benefits of permeable paving, changing to these materials is one of the easiest ways to increase the sustainability of a project.
It is for these reasons and many more that a range of incentives are now offered for project managers who incorporate permeable surfaces into their large scale projects.
Incentives for Installing Permeable Surfaces
The environmental benefits of permeable surfaces are evident, but did you know that installing these permeable surfaces could actually cut down the cost of a project?
Cost reductions are possible due to the generous subsidies and rebates available in many states for both residential and commercial projects that use permeable surfaces.
Almost every municipality offers some kind of incentive for using permeable paving materials, but there are far too many programs to mention them all individually. There is a useful list of rebate programs here.
Although each program is different, common features of permeable surface rebates include:
- Rebates per square metre of permeable surface installed, such as the Palo Alto program, which gives up to $10 000 in rebates for commercial projects using permeable paving materials for parking lots, walkways or patios 
- Incentives for the removal of old impermeable surfaces, such as the DC program which gives a $10 per sq/ft rebate for the removal of impermeable surfaces, which are replaced by permeable ones, limited to areas greater than 100 sq/ft in size .
- Tax rebates based on the measured amount of rainwater allowed to naturally infiltrate rather than enter the stormwater system, which is a part of the comprehensive rebate program in Minnesota 
When planning a new project, taking advantage of these rebates and deductions can greatly reduce the cost of paving and provide an ongoing tax benefit that lowers the overall upkeep costs.
In addition to the state and municipal programs, the installation of permeable surfaces can also help your project meet the standards for LEED certification.
Leadership in Energy and Environmental Design (LEED) is an initiative of US Green Building Council (USGBC) to measure the environmental impact of a building or project. Credits, rebates and refunds are often tied to the number of LEED points a project gains during certification .
The important thing to bear in mind is that LEED certification is tied to impact, not intent. Simply using an environmentally sound product does not qualify you for LEED points. There must be a measurable positive impact .
Two of the specific credits that permeable paving materials can be used to achieve are:
- LEED Credit SS-C6.1 Storm Water Management – Rate and Quantity
- LEED Credit SS-C6.2 Storm Water Management – Quantity Control
These credits are included in the LEED rating system to specifically address the issues caused by impermeable surfaces, as discussed previously .
In addition to these standards based on runoff, choosing the right material, such as a stabilized aggregate can help you to achieve standards such as:
- LEED Credit SS-C7.1 Landscape and Exterior Design to Reduce Heat Island Effect
- LEED Credits MR-C4.1/MR-C4.2 Recycled Content
- LEED Credit MR-C5.1/MRC5.2 Regional Materials
As you can see, making a smart decision about something as simple as the material for outdoor paths can help you meet multiple criteria for LEED certification, lower the environmental impact of your project and help you achieve rebates or tax credits.
The savings don’t stop there. Many of the most popular permeable materials are also cheaper to maintain in the long term.
Permeable paving materials can now be found at a similar cost to traditional non permeable materials and the economic case for using them is further improved by the lower lifetime cost .
Permeable materials, such as porous concrete, permeable asphalt or stabilizing aggregate binders such as Organic-Lock™ have proven to be more cost effective in the long term.
When looking at lifetime costs, a number of factors must be considered, such as:
- Installation and repair of stormwater infrastructure, much less of which is required for permeable surfaces .
- Stormwater fees charged by local governments, which are usually calculated based on the total amount of runoff .
- Repair and replenishment cost, which is typically higher for surfaces such as concrete and asphalt .
- Salting during winter, which is higher for impermeable surfaces due to ice build up on the surface .
- Stabilizing aggregate binders, such as Organic-Lock™ have the additional advantage of reducting overall surface maintenance when compared to their traditional counterpart (unstabilized aggregates).
As this feasibility study conducted for UC Davis shows, the need for ongoing repairs to both the impermeable surface and the necessary stormwater infrastructure add up to a significant amount over time . For a half acre parking lot, the cost over 25 years came in at $306,706.62 for permeable paving options, while impermeable pavements were projected to cost $371,356.28!
Clearly, choosing a permeable paving material for your next project makes sense both for the environment and for the bottom line.
Consult with an expert on permeable paving solutions today to find the right product for your needs.
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“Sponge City” in China—A breakthrough of planning and flood risk management in the urban context.
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