Incredibly, our standards for handling storm water today rely on methods first developed by the Romans more than 2000 years ago. The objective with this approach is to capture rainwater, channelize it and get it away from developed areas as quickly as possible — essentially disposing of this valuable resource. The method worked well enough for the Romans given their relatively small population, but in today's highly populated and highly urbanized world this methodology virtually insures that the world's water supply will continue to shrink at an ever-quickening pace, and ultimately will not be sustainable.
The LID paradigm is predicated on storm water management rather than disposal, and assigns this precious natural resource the value it deserves. Common LID strategies integrate green space, native landscaping and natural hydrological cycles that mimic nature. LID commercial and residential communities are more livable, more attractive and more environmentally sustainable. LID is simple and highly effective — and changing the approach with which we approach storm water management is critical to our future.
As impervious surfaces: concrete, asphalt and buildings, cover more and more of Houston's surface area, rainwater which once was held in vegetation, evaporated into the atmosphere or soaked into soil and eventually percolated into underground water tables, now runs off quickly and in huge volumes. The result is a rapidly declining groundwater resource,increasedsubsidenceand an urban flooding problem for which we're simply running out of answers. In addition, these high volume flows devastate natural creeks, bayous and rivers by carrying away banks and the vegetation that once held them in place. As the severe erosion damage mounts, these natural waterways become even less efficient at carrying away the water — so we build bigger, manmade channels, or widen and line the natural channel with concrete. These efforts are short-lived responses because they simply exacerbate the problem.
Equally negative, as the water is channelized and carried away, the pollutants such as the hydrocarbon-laden runoff from streets and parking lots are concentrated along the way. One pipe or channel full of concentrated pollutants feeds into another and another, and ultimately the load is discharged to the bays and estuaries on our shoreline. By the time it reaches the 'end of the pipe,' treating the pollution is just too big a job.
In an effort to make a dent in the runoff volume and pollution problem at one of the many sources, regulatory agencies now require Developers to implement Storm Water Quality Management Plans (SWQMP) for virtually every new commercial, multi-family or residential project. Unfortunately, the regulatory BMP responses are once again shortsighted, mostly ineffective and very costly.
Regulatory detention requirements mean that large surface storm water detention ponds are now a common component of most commercial and residential developments. These ponds may do a reasonable job of detaining water briefly and helping alleviate the flooding problem, but they waste vast tracts of valuable real estate, breed mosquitoes, rodents and tort liability issues. And although they're purported to have storm water quality treatment attributes, those attributes are mostly myth.
Costly underground storm water quality treatment systems are also now common components of these SWQMPs, but many treat only the first flush of storm water, leaving the balance to flow through the system unimpeded and untreated. Even worse, many designs promote the development of immense colonies of anaerobic bacteria that grow rampantly in the large volume of nutrient rich static water that remains inside between rain events — flushing the polluted water into the watershed with the next rainfall, and trading one problem for another.
These problems are all interconnected, and LID holds the answer to many of them. The costs Developers must bear to meet the shortsighted regulatory responses to the storm water problem are skyrocketing. The good news is that it seems we've reached "the tipping point"— the point at which it makes more economic sense to explore and implement alternatives rather than keep going down the same path.
Residential communities that were developed using LID principals have actually been in place for up to 20 years, and new ones ranging from a few acres to thousands of acres in size are being started across the country. Data on the benefits of LID is available to evaluate the results. Municipalities and counties in states from Maryland and Virginia, to Massachusetts and Washington, and all across the country have adopted, or are in the process of adopting, guidelines and new ordinances to encourage Low Impact Development.
If LID makes so much sense, why isn't it more widespread already? There are many answers ranging from fear of the unknown, to 'chicken or the egg' concerns with regard to local regulatory acceptance and permitting issues.
Another key issue also stands out. LID, with it's decentralized approach to storm water retention, typically uses widely dispersed "rain gardens" and "bio-retention cells" rather than large surface detention ponds, street-side swales rather than curb and gutter. These features should greatly reduce, if not eliminate traditional storm sewer infrastructure resulting in lower development costs and an increase in marketable land. It's one of the beauties of the concept, but the common methods used to achieve these goals are often seen as difficult to engineer and even more difficult to replicate. We believe it's been an obstacle to the acceptance of LID.
Systematic, replicable implementation of LID principles can be more readily achieved using a "system" by which volumes, tolerances and safety factors are more easily engineered. Such a system would follow LID ideals and enable them. Finding the answer meant looking to the other side of the world.
For more information on this subject, please contact us at 832.456.1000.
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