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| A "BIO CELL" CATCH BASIN |
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| WATER PERMEABLE ASPHALT... |
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| ,..AN ENTIRE STREET AND INTERSECTION |
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| STORM WATER/GREEN INFRASTRUCTURE EDUCATION |
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| A RAIN GARDEN |
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| CITY OF LACROSSE ECO PARK EDUCATION BUILDING |
Last Friday's Urban Forestry Council meeting in LaCrosse, Wisconsin was devoted to storm water management and "green infrastructure," the use of plants and natural systems to ameliorate flooding and reduce the need for hard scape engineering to control storm water. LaCrosse was a good place for the meeting, as it is located on the delta's of two rivers which join the Mississippi River and flood control is a major municipal concern.
So major that the city is experimenting with many innovative methods of flood water control, including what is now termed "green infrastructure," i.e., innovative water retention basins termed "bio cells," rain gardens, and water permeable asphalt, on a city-wide basis. Part and parcel with the actual use of these innovative methods, the city is doing experimental work, keeping detailed records of its efforts, and educating the citizenry of those efforts. It has even designed and built an entire educational park to demonstrate the practical use of "green infrastructure." The public is receptive to the city's efforts, since they experience flooding, often major, every spring.
At this point in time almost everyone is familiar with the concept of rain gardens, vegetation filled retention ponds built to slow down and absorb runoff water. In my own experience these devices are effective, but their overall usefulness depends upon maintenance to promote useful plants and eliminate weeds and trash. Without maintenance they soon become non-functioning eyesores.
Similar to rain gardens but a step further on the evolutionary ladder is the "bio cell," a fancy name for a more finely engineered rain garden. In this device, several feet of sub soil is modified to actually absorb and slowly release water into the water table, further diminishing runoff downstream from the retention pond. Here again, functionality depends upon maintenance. If road sand and debris are not removed the designed sub-soil will lose its absorptive quality. In any case the engineered subsoil has a life-span of about twenty years, after which it must be replaced. Bio cells may have plants as do rain gardens, or may be mowed grass. The entire concept depends upon proper engineering.
And, with either rain gardens or bio cells, location as well as maintenance is of the utmost importance.
Placed at the side of a road, parking cannot be allowed next to them, as anyone exiting the passenger side of a car will tumble into the depression. There are other practical considerations as well, such as who is to maintain the plants, or mow the grass, or pick up the trash. These are all good concepts but the devil is, as always, in the details.
I found the most interesting innovation of all to be that of porous asphalt, which is designed to absorb water, eliminating much of the need for catch basins and storm sewers. The stone aggregate is a little larger than that used in regular asphalt, and a polymer glue is mixed with the stones, eliminating the sand in the mix. This allows the asphalt to absorb water, which then bleeds away slowly through the larger stones of the road bed. We poured water directly on the asphalt surface and it simply disappeared. We were told a fire hose could be opened on the asphalt and the water would be absorbed. This technology is still in its infancy but the future is very promising. It is as strong as regular asphalt from the standpoint of vehicle weight, but it is more sensitive to abrasion from plows and tight turning vehicles so location and traffic must be taken into account in its use. Fine sand applied during winter can fill the interstices between the aggregate and reduce or stop water infiltration. I think this technology makes perfect sense for parking lots and other specific locations, if not for general road use.
Probably the most important fact I took away from the meetings and demonstrations is that green infrastructure has to be properly engineered and maintained. Digging a hole and filling it with good intensions is mostly wasted effort, but properly designed and maintained green infrastructure promises to solve a wide range of environmental problems.
One last cautionary comment on green technology, and one that can be applied to the entire environmental movement: in actual application, cost must be the determining factor. Not fuzzy math concerning eventual cost savings, but actual cost to design and implement new concepts. Prohibitive cost, particularly when, as is often the case, new concepts are mandated by law, will stifle economic growth. And if economic growth cannot keep up with the cost of new technology, the entire economy will decline, either causing new technology to be abandoned, or enormous public debt to be undertaken, the latter stifling the economy even more, causing a downward spiral into recession or even depression.
I personally believe that much of our current economic malaise is caused by over regulation and the mandating of expensive and unproven environmental concepts and technology. A case in point are new, vastly more stringent Minnesota regulations regarding building and site development. They are bound to stifle economic growth, particularly in manufacturing, or alternatively, new development will simply move elsewhere (think Texas).
If there is one over-arching principle I have learned in a lifetime of work in the environmental field, it is that only a very wealthy modern society can afford clean water, clean air and all the other environmental niceties that we Americans enjoy. If the planet is to be as "green" as we would like it to be, the entire world must be wealthy; that requires there be freedom, individual and economic, everywhere. Poor, hungry, uneducated, ill-housed and ill-clothed people do not have the luxury of worrying about green infrastructure.
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