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First Flush -- Stormwater

Gedunker

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Just finished meeting with a big box for their final plan review and they have revised their parking to include "first flush" areas. Googled the term and found an interesting variety of items (the best of which is from New South Wales EPA www.epa.nsw.gov.au/mao/ )

Anybody here in North America have experience with first flush requirements? Positive? Negative? Regulatory hoo-ha?
 

ludes98

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I have done permitting for various big and small box. Never done first flush. Some juristictions require oil separators, but that works for all flows. First flush is nice concept, but how does the change to the rest of flow occur?
 

Rem

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We have a standard requirement on new development to install first flush systems. On site for large developments, in collected off-site systems for smaller developments (eg. greenfield residential developments). In some situations it is not physically practical to provide a system so we look to overcompensate in another sub-catchment.

We are also retro-fitting systems in established urban areas.

We are a City around a lake - most of our SW drains to that lake (small amounts to the ocean and some to another river system). They do work - we have about 10 - 15 years experience with them and they are getting better as the science and practice improves. We monitor to measure effectiveness.

The purpose of a first flush system is to capture SW borne contaminants which are in greater concentrations during the first stages of a storm event. The latter stages bypass the first flush system as that SW is regarded as relatively clean. We may have other detention measures in place to deal with downstream flooding, but they come later in the process.

I'm not the expert on this but if you have specific questions I can ask one of our in-house experts to respond.
 

Gedunker

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Thanks, REM I knew I would get a good explanation from you. I appreciate it.

This is such a new concept to me that I really haven't any idea of how these things operate (in the regulatory sense, not the scientific sense). Skeptic that I am, I imagine that if a US big box retailer is voluntarily installing this technology there must be municipalities that are requiring them.

Our SW ordinance requires post-development run-off to equal pre-development run-off and that's about it. Even with new SW pollution mandates from USEPA, we have not adopted anything to treat point- and non-point-source SW pollution.

In your experience, are most of the first flush catchments treated on-site or hauled off for treatment elsewhere? I don't believe that our publicly-owned treatment works (waste water) would accept this SW, so I am wondering where they will treat it. If it is treated on-site (the retailer did not show any facility for that, but I'm wondering anyway) are there noise, vibration, odor issues to be aware of?

Any help will be appreciated.
 

Rem

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Sorry Gedunker, you posted your questions when I wasn't very active on the boards due to work commitments and I've only just seen them.

Most SW pllution is dealt with off-site. A typical arrangement would be a trash rack, followed by a GPT (gross pollutant trap) then an artificial wetland to deal with suspended solids and nutrients.

The trash rack removes litter, larger debris, children etc. The GPT removes most of the sediments and suspended solids. The wetlands assimilate nutrients attached to suspended sediments and dissolved nutrients. In the wetland plants are harvested, usually with a long reach excavator from time to time to encourage new growth and maximise take up of nutrients. Sediments trapped in the GPT and the wetland itself can be contaminated with heavy metals (road wash, industrial fall outs) and are tested prior to disposal. They are removed by Bobcat or backhoe, depending on the design of the facility. Depending on the level of contamination such material may end up at our worm farm, land fill or be further treated. The removed material needs to be dewatered, usually on-site prior to disposal and that can be an unsightly procees (ie. big pile of muck) depending on how exposed the site is.

There are situations where there isn't enough room to treat run-off on-site or even in a down stream facility. A 'proprietary system' (this is the terminology used by our engineers to describe pre-fabricated units that are inserted into the drainage line) may be installed as an alternative. This may only be able to separate gross pollutants or it may skim for hydrocarbons as well. These types of facilities may dispose to the sewer under a special licence, but will pay heavily for the privilege. Pump out and further treatment of effluents is more typical. They are generally collected by a sucker broom (street sweeper with giant vacuum hose attached). The material from these facilities may also require testing depending on the catchment.

Odours haven't been a problem for us (at least that I am aware of). If it is a propriatary system your developers are offering, they tend to be underground, so that should help.

There is literally mountains of information on the science of these systems. Our own requirements are set outhere, select Download F and go to section 2.5.3. As you can see there is no single right solution - we have performance criteria established and deemed to comply solutions.

There is a big box centre nearby that has installed a wetland (one of the on-site examples) that I will try to get some photos of for you. Please be patient though.

Once again sorry for the delay - hope this is of use.
 

Rem

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jordanb said:
The ultimate solution to polluted runoff: http://www.mwrdgc.dst.il.us/plants/tarp.htm;)
Wow. We could never afford it.

Despite all thew pats on the back, I wonder if the off-site impacts are all that benign - where did the rock go? What are the reservoirs replacing? What happens to the waste water in te reservoirs? Where is the disincentive to pollute?

JordanB I noted your smiley, so I guess you are sceptical as well.
 

Gedunker

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Thanks, Rem. The developer of the big box has scaled back his "first flush" plans but intends to "rough in" the proprietary system for completion at a later date. As we do not regulate storm water treatment, we can't compel anything greater. It's a start, I guess. I've downloaded your link and will take a look at it when things slow down a little bit.

Jordanb your link was ... interesting. |-)
 

Cardinal

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Chicago's Deep Tunnel had its share of problems early on, but I think has come to be an effective part of the metro region's water quality program. Back in the 1980's all Chicago-area communities were compelled to separate their storm and sanitary sewer systems. During a major storm, water is stored in the deep tunnel until it can later be pumped out and treated prior to release. On the one hand pollutants have been removed from the water. On the other hand, the environment still misses out on the benefits of natural systems such as wetlands and infiltration.
 

jordanb

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The wink was because this system could never be used in such a low density environment.

Howver, TARP has been a wonderful sucess in Chicago, so much so that dozens of cities are now falling over themselves to build their own deep tunnels. Also, the boring machines used in the Chunnel were invented to dig TARP.

Interestingly, TARP was built just because Chicago's sewer system is combined. If Chicago's sewars were built today, they probably would have been seperated and the runoff water would have gone untreated. First flush systems would have been impractical because there's not space for on-site systems (plus a much more significant amount of the runoff is from streets than parking lots), and off-site systems would have required an army of trucks to move all of the waste around after every rain, causing more problems. Here, the water moves itself through the deep tunnels to the treatment facilities.

Not only that, but TARP results in cleaner water because every drop of runoff gets treated, not just the first inch or two. Once it's finished, it will only be overwhelmed by five year events, meaning, on average, there will only be a discharge every five years. That means that, except for about two events a decade, every drop of runoff from Chicago will be treated. Before TARP, there were discharges every two weeks or so, with about five backflows into the lake a year. Now it's down to just a few discharges a year and both the river and the lake are remarkably more healthy.

I think TARP is a good example of how density can be more efficient and healthy for the ecosystem than sprawl. TARP would never really get built in LA because the economics wouldn't work out, so they're stuck with an open sewer type river full of polluted runoff, while Chicago is well on its way to pristine waterways.

Also it's proof that sometimes, just sometimes, massive engineering projects actually do solve the problems they set out to solve without creating a whole host of new problems. ;)

Here are some more articles about deep tunnels:
http://www.chicagotribune.com/news/local/chicago/chi-0312110047dec11,1,7252550.story
http://www.canoe.ca/CNEWSFeatures9907/01_lakes.html
 

Rem

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JordanB thanks for the extra information.

There is a bit of this sort of thing happening in Adelaide (Capital of South Australia) where they are using ground water recharge to 'store' stormwater for later reuse. Where sub surface conditions permit (fractured granite), water is diverted to the ground. Being a very dry place overall, the water is later reclaimed for non-potable uses. One problem with ground water recharge can be a rising water table. It may bring minerals closer to the surface, ruining soil structures and rendering affected soils unsuitable for supporting vegetation. Salination has occurred extensively in irrigation belts in Australia.

I see your point about every drop of SW being treated, but a first flush system treats a very high percentage of the pollutants, concentrated in a small amount of the water. It's likely it was covered in the Chicago project, but the natural systems downstream of the City probably rely on a certain level of nutrients and water (including storm flows) to sustain themselves. If they were removed completely, the natural system may fail.

Thanks again for the detail - it is an amazing project that I hadn't heard of before.
 

Michele Zone

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This is really interesting and I have done a little surfing to try to understand it better, in context. But, alas, I don't have the time to do a thorough job at the moment.

A couple of points:
JordanB's comments that a "5 year event" means that the system will only be overrun twice a decade is something I am really skeptical of. I would want to see the actual wording and definition of the source. If the expression "5 year event" is used in the same way that the phrase "100 year flood" is used, then its actual definition would be "an event with a one in 5 chance of happening in any given year" rather than "an event which happens once every 5 years". Additionally, when data on river flood levels et al are gathered over a longer period of time, estimations of the size of a so-called "100 year flood" typically go up substantially.

On top of that, urbanization dramatically increases flooding, in terms of frequency and severity, by every measure: flash floods increase, volume of the flood increases, and so on. I realize that Chicago is already highly urbanized but that doesn't mean there isn't room for yet more surface to be paved over. I would be interested in seeing the long term outcome -- whether this system actually does what it is expected to do or whether it becomes overwhelmed and outdated far quicker than is expected.

I am generally skeptical of any claims that a very large scale engineering project has achieved its ends without causing a whole new set of problems. The Aswan Dam is sort of the "poster child" for large scale engineering projects that beautifully achieved all of its objectives but with disasterous and unexpected "side" issues. I don't know if I have given my "rant" on that subject here before or not. The really, really short version is that one of the objectives of the project was to "control flooding" of the Nile River. Uh, Hello?!! Flooding of the Nile River is why Egypt is called "The Jewel of The Nile". Use of chemical fertilizers has increased dramatically -- for those who can afford it -- poor farmers who can't afford to buy fertilizer have been hurt badly and incidence of Schistosomaiasis has reached epidemic proportions. It turns out that all that icky flooding also kept the snail population under control -- and the snails are the vector for this incredibly nasty parasitic infection, which is typically caught when barefoot farmhands step on snails in the irrigation canals. (I could go on, but I *am* trying to be brief!)
 
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Rem

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Michele Zone said:
On top of that, urbanization dramatically increases flooding, in terms of frequency and severity, ....Chicago is already highly urbanized but that doesn't mean there isn't room for yet more surface to be paved over. ....
The two main SW issues are getting crossed over here. First flush deals with the most polluted SW and is primarily about water quality. Flooding is a water quantity issue and needs different solutions.

There are opportunities to improve detention in urbanised environments too. It can include rainwater tanks, pervious pavements, detention ponds, pipe systems with inbuilt detention capacity. Gedunker mentioned elsewhere that they require post development flows to mirror pre-development flows. This is the standard we apply to detention. If a developer can't achieve it on site, they can contribute to a larger downstream facility, or over compensate in a complementary sub-catchment.
 

Michele Zone

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Rem, I don't see it as that simple and clear cut. I had to take an introductory hydrology class as part of my major. Water issues are not so neatly chopped up into pieces. Pavement interferes with many natural processes that filter and process the water in a way that allows for ground water/ aquifer recharge, cleansing of the water, etc. The promotion of flooding seems to me to be directly related to what you are talking about. It sounds like this thread is about "how to deal with the sheets of polluted water washing off of a large parking lot immediately following the initial downpour?"

Well, in Europe, you see a certain amount of porous solutions in place of sidewalks and roads: cobble stone streets of old, and little hexagonal pavers that allow for grass to grow in between, etc. Permeable solutions to parking lots and ways to include some greenery, etc, would ameliorate this whole issue. They have done some studies on what types of plants process large volumes of water more effectively and which ones handle pollutants better, both in terms of survival and in terms of filtering them out of the environment. The types of plantings you have in an aquifer recharge zone dramatically impacts how much water actually recharges to an aquifer.

Humans may artificially impose a mental categorization on different aspects of water flow but nature does not. In fact, they are finding increasingly that our artificial separation of "air pollution", "water pollution", etc is a loophole for polluters: if you can't put it in the air, then you can dump it in the water to remain legal without really doing much to change what you are doing.
 

giff57

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Michele Zone said:

If the expression "5 year event" is used in the same way that the phrase "100 year flood" is used, then its actual definition would be "an event with a one in 5 chance of happening in any given year" rather than "an event which happens once every 5 years".
I think Michelle just out statisticed (yes that is my word) JordanB
 

Rem

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Michele Zone said:
Rem, I don't see it as that simple and clear cut. ....
I'm saying that first flush systems address water quality. They are not designed to deal with large water volumes and by definition ('first flush') avoid dealing with all the water from a storm event. It's an extension of the 80/20 rule - you get 80%of the pollutants by treating 20% of the water (although we aim for higher removal). I don't suggest water quality and quantity control systems can't be complementary or work in unison - but it is a different goal to improve water quality as opposed to reducing downstream flooding or replicating natural storm impacts after development occurs.
 

Michele Zone

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I do get your point Rem, I really do. And I understand why you have the perspective you have. But, again, my view of it just isn't that cut and dried. "First Flush" of water going across pavement is an artificial, man-made mini-flood event. In nature, you get that kind of runoff in some environments -- like deserts, where the ground is so hard that it doesn't readily absorb water -- but, for the most part, flooding in nature occurs AFTER substantial rain has occured, the ground has reached saturation and no more can percolate as fast as it is coming down out of the sky. (And runoff is flooding. I am not talking apples and oranges.)

Water quality and water flow being "separate issues" is a man-made, artificial categorization that nature does not make. The two are intricately intertwined. Without the flow process, there is no such thing as "Potable water".

In brief: Oceans contain 97.41% of all water. Which means that only 2.59% of water is "fresh water". However, most of that is contained in glacies and polar ice caps: 1.984% of the total. This leaves only 0.592% of all global water as "groundwater" and 0.014% to divide up between lakes, rivers, atmospheric water vapor, soil moisture, and "biota" (that would be the water in my body and yours, plants, etc.). This is from p.491 of "Living in the Environment, 10th edition" , G. Tyler Miller Jr.

In round numbers, that means about 3% of all water on earth is fresh water, and 0.003% is "readily available fresh water". If some of y'all aren't familiar with it, you can check here: http://www.epa.gov/quality1/ or here: http://www-k12.atmos.washington.edu/k12/pilot/water_cycle/grabber2.html for a diagramattic overview of how that miniscule percentage of water has to cycle through the air, ground, oceans, etc on a continuous basis in order to remain fresh and readily available. Water that isn't flowing properly through these complex processes isn't going to be good quality. And pavement prevents natural processes like percolation. So, really, this is a water flow issue that results in pollution and not a separate issue.

I really don't want to belabor the point and I have nothing to really add to the topic that is supposed to be under discussion in this thread. But JordanB brought up a much more complex issue with the link he gave. If, like Gedunker needs to for his job, you want to just look at how one deals with the highly polluted runoff from a large sheet of paving called a parking lot -- well, you are The Man and I won't argue your expertise. But I decided to get my bachelor's in an environmental studies program so I would have a deeper understanding of environmental processes than what our present practices and policies typically incorporate within their body of wisdom, knowledge, and experience.

America focused all of its initial water quality legislation on "point source pollution" -- aka "the end of the pipe" coming out of some plant and dumping awful things into the river. They have addressed that very well. And now much of our problem is "non-point source pollution" -- aka runoff of the type under discussion in this thread. It is much harder to address because you can't just "cap" the source, like with a pipe. (And they are beginning to have issues with these two definitions because if the water ends up in a ditch which ends in a pipe, well, now you have a "point source.") Which means that the standard for dealing with non-point source water pollution is "best practices" methods of preventing the pollution to begin with, not treating it after the fact.

Uh, as I said, I don't want to belabor my point. So I will spare you the rest of my thoughts on the topic. In no way do I mean to argue with you. But I have intentionally chosen to NOT limit my view of these issues to the way that present practices frame these problems. In short, to quote Einstein: “Problems cannot be solved at the same level of awareness that created them.” So I do not expect our present environmental problems to be solved by our present policies and view of what creates them. If that view were adequate, we wouldn't be in the mess we are in.

EDIT: coincidentally, I am moving bookmarks and tripped across this: http://www.epa.gov/ost/basins/ Better Assessment Science for Integrating Point and Non-Point Sources (a GIS for American watersheds).
 
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tsc

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Our county has a Stormwater Management Planning Manual that is available online at

Westchester County Stormwater Management Planning Manual

We often suggest communities require developers follow these guidelines. Much of our county is located in the NYC watershed.

The manual, however, does not really refer to the exact topic of this thread....first flush.
 

jordanb

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Michele Zone said:
This is really interesting and I have done a little surfing to try to understand it better, in context. But, alas, I don't have the time to do a thorough job at the moment.

A couple of points:
JordanB's comments that a "5 year event" means that the system will only be overrun twice a decade is something I am really skeptical of. I would want to see the actual wording and definition of the source. If the expression "5 year event" is used in the same way that the phrase "100 year flood" is used, then its actual definition would be "an event with a one in 5 chance of happening in any given year" rather than "an event which happens once every 5 years". .
Of course that's what it means. Rainstorms don't tend to be regular. Notice I said "on average" and "about." I was putting the idea of a five year event in context. Granted, it's possible could be ten five year events in one decade, and none the next. On average though, they will occur every five years.

Additionally, when data on river flood levels et al are gathered over a longer period of time, estimations of the size of a so-called "100 year flood" typically go up substantially.
This is measuring rainstorms, not floods. Not sure what kind of difference that makes.

I actually did "back of the napkin" calculations to come up with a five year event. The current Chicago sewer system (which is needed to deliver the water to TARP) is designed to handle that, but having TARP might increase the capacity of the sewers by moving water through them faster. Plus, it has capacity for 3.6 inches of rain runoff. Not knowing how quickly the treatment plants process the water or how much rain can be stored in the sewers, I'm guessing that comes out to about a 4.5 inch+ rain (more if it falls more slowly). That sounds like about a five year event.

On top of that, urbanization dramatically increases flooding, in terms of frequency and severity, by every measure: flash floods increase, volume of the flood increases, and so on. I realize that Chicago is already highly urbanized but that doesn't mean there isn't room for yet more surface to be paved over.
Well, the region we're talking about is nearly totally built-out, except for infill, which is more likely than not to be replacing a paved or gravel lot and actually might decrease the runoff. There might be some increses, but it likely won't be more than a few percentage points difference ether way.

Also, the focus nowdays isn't on paving over as much as possible. Now, the emphesis is on combining nature with the city, opening up greenspace, etc.

Plus, the possibility of more reservoirs will exist.

I am generally skeptical of any claims that a very large scale engineering project has achieved its ends without causing a whole new set of problems.
Any?! How about the Panama Canal? Closer to home, how about the Sanitary and Shipping Canal in Chicago? Before it was built, Chicago was known as "typhoid city," with some of the worst drinking water in the world. Horrible epidemics were part of the routine. Afterwards, Chicago had one of the safest and cleanest water supplies in the world. Granted, the river was still an open sewer, and that wasn't addressed until the 1930s when the first treatment plants were built, and serious progress wasn't made on cleaning it up until TARP, but the S&SC fulfilled its objectives with even fewer side effects than were suggested before it was built (like, for instance, the fact that it did not seriously pollute the Mississippi river system).

The Aswan Dam is sort of the "poster child" for large scale engineering projects that beautifully achieved all of its objectives but with disasterous and unexpected "side" issues.
I'd be very suprised if the side effects of the damn weren't well understood before it was built. More likely, they just weren't acknoledged by the authorities at the time. A similar thing is happening now with the Three Gorges Dam, which will be an ecological disaster on a similar scale when completed.

Fact is, there are many large projects from throughout history that were very sucessful by any measure, as well as ones that were miserable failures. It's becoming increasingly obvious that the single largest project, the Interstate System in the United States, was a failure, for instance, but assuming that just because a project has a large scope, it will be a failure, is overly simplistic.

The TARP is already a sucess. If they quit building it right now, it has already cleaned up the river and lake so much that it would be an unparalleled success.

Look at this:


The building on the right is just a few years old. These are new residential developments along the river. Now, being along the river is such a huge draw, since it dosen't reek, that it's spurring millions of dollars of development in the city. Not to mention the increased livability of the city that comes from having a clean river and a lake that's safe to swim in, and to mention the already incredible flood control the TARP has provided for the city.
 
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Michele Zone

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jordanb said:

but assuming that just because a project has a large scope, it will be a failure, is overly simplistic.

I appreciate your in depth response. As an aside, I would like to note that the somewhat inflammatory tone is undoubtedly why so many people are not terribly fond of you. You are young and undoubtedly brilliant. But please do not assume that I am stupid. I am not assuming anything and my view of things is rarely "overly simplistic".

I appreciate your clarification that we are using the terminology for flood events the same way. Unless Chicago deals with a great deal of flooding due to snowmelt in nearby mountains coming down stream or other flood events coming downstream from elsewhere, I think you can kind of assume that excess rainfall and flooding will be largely synonymous. However, having spent a great deal of time in the South, that may be largely personal bias. :)

The side effects of the Aswan Dam may or may not have been well understood beforehand but, from what I have read, the people who planned it and built it did not expect them at all. Which is precisely my point about why I chose an environmental studies degree: there is a great deal of expertise out there but it tends to not be the type of thing which interests planners. In fact, it isn't my first love either. I consider this degree program to be something of a personal sacrifice since science is not my favorite subject. But I did not want to have the same blind spots as "most" planners. I wanted to bring an entirely new set of blindspots to the profession. ;)

I am sure they are shocked about the outcome of the Aswan Dam if only because the extremely rapid pace of accumulation of sediment behind the dam is expected to give the dam a much shorter lifespan than intended. Which means it was a very expensive project that will not be around terribly long. If you are actually interested in the pros and cons of that project, I can pull out a textbook or two and give you some additional information.

I haven't studied the other projects you mention. Therefore I am in no position to discuss them. However, I would like to note that it can be very hard to pin down cause and effect and that, just because the literature doesn't cite a downside, doesn't mean there isn't one. Nor do I think that the new set of problems is automatically going to be 'not worth it'. I do not make judgment calls in such a simplistic fashion. As one example from Cyburbia, I recently criticized vaccines but then turned around and defended their value. The fact that there are problems with vaccines, some of which are very serious and the scope of which has yet to be fully determined, does not mean I wish to go back to pre-vaccine days of rampant polio, etc. Generally speaking, things are not often "black and white", "all or nothing".
 
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Gedunker

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As the thread starter, I would ask that we refrain from any types of personal attacks. If I see any more it, I will immediately contact a mod and have the thread shut down or removed. Let's stay on topic.

The topic is of specific importance to an aspect of urbanism and ecological quality that is worthy of discussion and there may be differences of opinion in how to achieve the goals of development and/or redevelopment with respect for the environment. We must all agree on this goal.

MZ I am the floodplain administrator for my city. I work long and hard to end the use of the term 100-year floodplain and replace it with "1% flood" (as FEMA and Indiana Department of Natural Resources/Division of Water are also trying to do). Lay people are too willing to risk their lives and possessions when they think in terms of 100 year increments. They are only too happy to remind me that "it didn't even get close to my property in the 19__ {fill in the blank} flood". It grates on me like fingernails on a chalkboard.

Jordanb the project in Chicago has been a great success form all I've read about it. Its portability to places like my city (pop 38,000) depends on both the ability to pay for it and geologic features. We fail on both accounts, especially as we are situated on a form of shale that has near-zero percolation capacity.

Finally, I believe Rem is right that water quantity and water quality is issues are distinct, but that they can be complimentary in creating a healthier livable environment.

Let's get back now to the first point of the post -- practical implementation of this technology. Thank you.
 

Michele Zone

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Gedunker said:

MZ I am the floodplain administrator for my city. I work long and hard to end the use of the term 100-year floodplain and replace it with "1% flood" (as FEMA and Indiana Department of Natural Resources/Division of Water are also trying to do). Lay people are too willing to risk their lives and possessions when they think in terms of 100 year increments. They are only too happy to remind me that "it didn't even get close to my property in the 19__ {fill in the blank} flood". It grates on me like fingernails on a chalkboard.

Let's get back now to the first point of the post -- practical implementation of this technology. Thank you.
I wasn't aware that FEMA was trying to change this. I think that is a good idea. I was surprised when I learned the definition. The term is very misleading.

I glanced back over the thread. I note Rem mentioned artificial wetlands. Earlier this year, I did some research on valuing wetlands and in the process came across some data on their value in purifying water. Here is one link that briefly quantifies that value: http://www.ramsar.org/values_waterpurification_e.htm

And here are some design criteria for artificial wetlands, if you are interested: http://www.state.sd.us/denr/des/P&s/designcriteria/design-16.html
 
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