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Red Pill or Blue Pill

For some, the 1999 sci- movie The Matrix accurately characterizes a world with two realities. The story is about a giant matrix of interrelated computer programs that creates a machine-based manipulated world; the other world, the real world of humans, is tormented by the machines and forced underground to survive. Their means of entering and leaving the Matrix is via airships that travel through the underground utility chambers packed with sewer pipes. At times the humans disrupt and reprogram Matrix computer codes to survive. Eventually a savior, Neo, emerges to tame out-of-control machines disguised as humans. His biggest revelation is that the Matrix is a fabricated, digital reality. He learns how to operate above and outside it, so that he can eventually defeat the wayward machines.

This dual reality seems to exist in the stormwater management world. The Matrix exhibits itself as soulnumbing impervious pavements like sidewalks, plazas, parking lots and streets, mostly supporting petroleumfueled transportation, mostly computer generated. This reality is that big institutions support such pavement. The reality of the stormwater community, the smaller and less inuential folks who try to reduce stormwater runoff, seems to be slowly nibbling away at the programmed path of the Matrix. This begins with permeable pavement, often energized by runoff regulations, and when deployed, the Matrix programming seems to yield.

This magazine issue demonstrates some evidence. The feature article on permeable interlocking concrete pavement sidewalks and a parking lot in downtown Raleigh, NC, could have gone conventional under the inuence of the Matrix. However, a human intervened and redened the surface, reduced runoff, and increased the possibilities for friendlier urban places. Another Raleigh space is shown in the photo, a green alley between two buildings just blocks from the Governor’s house. Again, someone intervened and reprogrammed this part of the Matrix.

Two other things might reprogram the Matrix: research and specications. These can point it toward the humanizing reality of permeable pavement. An article in this issue notes the ICPI Foundation is supporting permeable pavement research. While research results support the stormwater community, the transportation folks (i.e., local and state DOTs) will only condently embrace permeable pavements for applications beyond lowspeed residential roads when structural testing and design charts for base thicknesses become available. The article notes that research on this is about to start at the University of California at Davis, and this effort is supported by the California concrete paver and cement industries.

Another reprogramming of the Matrix lies with dissemination of experiencetested specications placed into state transportation agency manuals and municipal construction guidelines. The challenge is that each specication is written in the language of each agency with references to their materials and test methods. Each specication requires technical review to minimize transportation agency risks. That’s a lot of specs taking a lot of time to change.

However, the Matrix at its core is a multiplicity of interconnected networks. And like the conclusion of The Matrix trilogy, the ultimate transformation of transportation agencies to permeable pavements will be viral. For now, the stormwater management world and the concrete paver industry are building the programming to make that happen.

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Win-Win Situation

Leaders in the concrete paver industry co-host special event to showcase the benefits of sustainable paving options.

In an effort to advocate increased adoption of permeable pavement solutions by the environmental protection and transportation agencies, EP Henry and ICPI (Interlocking Concrete Pavement Institute) jointly hosted a special event and demonstration for U.S. Representative Frank A. LoBiondo (NJ-02) yesterday at the Woolwich Township Municipal Building in Swedesboro, NJ.

Sustainable paving options, such as permeable interlocking concrete pavers manufactured by EP Henry and other ICPI members, allow water to infiltrate into the surface through joints between the interlocking paving units and into a stone base that stores and infiltrates water into the soil. Unlike most paving systems, such as asphalt or concrete with impervious surfaces, environmentally friendly permeable interlocking concrete pavers reduce stormwater runoff, as well as pollution of our waters, and help control flooding.

Permeable pavers can help meet local stormwater regulations, contribute to earning potential LEED® credits, and reduce drainage costs compared to conventional retention ponds. Additionally, permeable pavers are highly attractive, durable, easily repaired, require low maintenance and can withstand heavy vehicles, making them an ideal paving solution for large-scale transportation projects.

“Concrete pavers play an important role in local construction projects and our small business-driven economy,” said Congressman LoBiondo. “In addition to laying the foundation for safe infrastructure and beautiful communities, they are helping to grow our economy while finding innovative ways to help protect our environment. Whether it’s technology to help overcome flood control problems or improving water quality via stormwater filters, it’s a win-win situation.”

Congressman LoBiondo is a member of the House Transportation and Infrastructure Committee. The House Committee was instrumental this summer in passing MAP-21, a comprehensive transportation bill that authorizes the expenditure of $105 billion for highway and other transportation construction, research and demonstration projects throughout the United States. MAP-21 is the most important federal legislation influencing transportation policy in America.

Earlier this year, ICPI succeeded in lobbying Congress to include in MAP-21 first-ever permeable pavements provisions conceived by ICPI and offered for consideration on Capitol Hill. The new permeable pavement provisions are intended to help state and local governments—including those in New Jersey—overcome institutional barriers to adoption, so that permeable pavers can be used in projects to help reduce stormwater runoff and flooding.

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Alleys Go Green with PicP

Green alleys, using permeable interlocking concrete pavement (PICP), require careful consideration during the design stages. Start with the end in mind, specifically calculating the amount of water that needs to be managed and where it is draining.

The first steps of the project are calculating runoff volumes from adjacent pavements and buildings, as well as timing how quickly water moves from roofs to the alley and into storm sewers.

In downtowns and highly urbanized areas, alley sewers receive roof runoff from downspouts and adjacent pavements. Green alleys provide a means to slow this flow, and in some cases, infiltrate a portion of the water into the soil subgrade. Slowing the flow can be done with berms and/or constricted outflow pipes that pool into catch basins before draining into the larger sewer system.

slow the flow

Berms are often required to slow flows when the subgrade slope exceeds 3 percent. Berms can consist of concrete, soil left in place, or lateral trenches dug across the width of the alley. The simplest berms consist of an open-graded base wrapped with two layers of geotextile, sitting atop the soil subgrade. Regardless of the material, the height of each berm depends on how much water needs to be detained and infiltrated (if soils are cooperative). Modeling flow is characterized by small ponds flowing one into the next. The outflow from one to the next can be via sheet flow, a knotch, or through a pipe (or pipes) penetrating the berms and aligning with the slope (i.e., oriented longitudinally).

Roof downspouts should drain water into the PICP base instead of its surface if there is an abundance of adjacent impervious surfaces. This reduces the risk of downspouts draining across impervious pavement and mobilizing sediment into the PICP openings. In addition, downspouts joining PICP base will flow longer in winter. In suburban settings, water from downspouts can run across vegetated areas, allowing for infiltration. Estimating the amount of runoff from the vegetated areas should assume the worst-case scenario for saturated soil infiltration rates.

modeling extremes

Depending on the geographic region, there could be extreme storms and rainfall depths that cannot be drained by the alley. When designing a green alley in these areas, the conditions that create flooding need to be modeled (i.e., the worst-case flooding scenario, including the depth and duration of standing water). If surface or subsurface bypass pipes or overland passages drain water from extreme rainfalls, all the better. If not, then the alley should be designed to minimize adjacent property damage in the event of deluge and flooding.

In downtowns and highly urbanized areas, alleys run next to building foundations. The foundations or sides of the alley will require covering by an impermeable liner to prevent water from infiltrating building foundations and basements, especially if the alley is designed as a detention/infiltration facility. This can be accomplished with restricted outflow pipes or perforated pipes along the soil subgrade that hold water until it deepens and then flows out of elevated drainpipes. In other instances where soil infiltration is negligible, there may be perforated drain pipes at the bottom of the alley that remove water almost immediately, which might obviate the need for liners against foundations.

Alleys often have utility poles that should not be surrounded with open-graded base. The utility poles should be moved or the open-graded base should be directed around them. They should be treated as structures; therefore, impermeable liners should be placed several feet away from their perimeter. Another option may be encasing the underground portion of the poles in concrete. Consultation with an engineer from the company that owns the poles is essential. The depth of the poles and distance of undisturbed soil around each should be discussed.

Alleys may have some distance between the back of the buildings and the alley surface. This space can be lawn, a separate garage or outbuilding, or gravel or dirt parking spaces. To reduce the risk of sedimentation and clogging, consider paving these surfaces with permeables as well. PICP alleys require curbs, which occasionally can be sloped to block or divert water and sediment flows from adjacent parking spaces away from the permeable surface.

Alley maintenance is almost non-existent in many cities because surface cleaning, snow removal and deicing are not budgeted. All permeable pavements for green alleys will require regular surface vacuuming. Because some sewer authorities have installed green alleys, they have assumed surface cleaning, especially if the city doesn’t maintain alleys. Surface cleaning is essential, because incidental litter from trash, leaves and grass clippings can accumulate on alley surfaces. For whomever maintains the alleys within a city, green alleys should be included in computerized pavement or sewer management systems.

transforming character

Underground utilities generally are not an issue, as long as they consist of waterproof piping and are deep enough to survive compaction of stone base materials over them without damage. Keep in mind that some utility lines are encased in open-graded stone, and that stone can be a pathway for water if adjacent to a permeable pavement base. In such cases, the flow of water onto the stone around a pipe exposed at the side of a permeable pavement excavation will need to be stopped with low-strength concrete fill.

When alleys go green with PICP, they can be paved with light colored paving units, which can enhance night lighting and help reduce urban temperatures. Alleys in older cities are often made of stones or bricks, and PICP can take on the appearance of either surface, thereby preserving and reinforcing the paving tradition and design context of these older cities.

The transformation from an unsightly alley in a backyard to a clean, well-kept space may increase private property values and earn money for the city in the form of higher property taxes. And for cities with combined sewers, green alleys are another effective tool in the green roads/green infrastructure toolbox that can reduce combined sewer overflows with stormwater detention and infiltration.

Combined sewers or not, green alleys can increase a neighborhood’s character and provide much-needed public spaces in dense urban areas.